By Matt Price


2011-03-06 12:43:57 8 Comments

I'm new to iOS and Objective-C and the whole MVC paradigm and I'm stuck with the following:

I have a view that acts as a data entry form and I want to give the user the option to select multiple products. The products are listed on another view with a UITableViewController and I have enabled multiple selections.

My question is, how do I transfer the data from one view to another? I will be holding the selections on the UITableView in an array, but how do I then pass that back to the previous data entry form view so it can be saved along with the other data to Core Data on submission of the form?

I have surfed around and seen some people declare an array in the app delegate. I read something about Singletons but don't understand what these are and I read something about creating a data model.

What would be the correct way of performing this and how would I go about it?

30 comments

@kaar3k 2012-05-23 13:08:30

This is a very old answer and this is anti pattern, please use delegates. Do not use this Approach !!

1. Create the instance of first View Controller in the second View Controller and make its property @property (nonatomic,assign).

2. Assign the SecondviewController instance of this view controller.

2. When you finish the selection operation copy the array to first View Controller,When u unload the SecondView ,FirstView will hold the Array Data.

Hope This Helps.

@Matt Price 2012-05-28 14:49:23

I don't believe this is the correct way to go as it creates a very ridged link between view controllers. Not really sticking to MVC.

@kaar3k 2012-06-04 14:07:15

If you want to strictly follow MVC, use NSNotificationCenter a method can be called from ViewControllerA to ViewControllerB ,check this it might help u

@swiftBoy 2019-05-19 14:24:47

Swift 5

Well Matt Price's Answer is perfectly fine for passing data but I am going to rewrite it, in Latest Swift version because I believe new programmers find it quit challenging due to new Syntax and methods/frameworks, as original post is in Objective-C.

There are multiple options for Passing Data between View Controllers.

  1. Using Navigation Controller Push
  2. Using Segue
  3. Using Delegate
  4. Using Notification Observer
  5. Using Block

I am going to rewrite his logic in Swift with latest iOS Framework


Passing Data through Navigation Controller Push : From ViewControllerA to ViewControllerB

Step 1. Declare variable in ViewControllerB

var isSomethingEnabled = false

Step 2. Print Variable in ViewControllerB' ViewDidLoad method

override func viewDidLoad() {
        super.viewDidLoad()
        //Print value received through segue, navigation push
        print("Value of 'isSomethingEnabled' from ViewControllerA : ", isSomethingEnabled)
    }

Step 3. In ViewControllerA Pass Data while pushing through Navigation Controller

if let viewControllerB = UIStoryboard(name: "Main", bundle: nil).instantiateViewController(withIdentifier: "ViewControllerB") as? ViewControllerB {
        viewControllerB.isSomethingEnabled = true
        if let navigator = navigationController {
            navigator.pushViewController(viewControllerB, animated: true)
        }
    }

So Here is the complete code for :

ViewControllerA

import UIKit

class ViewControllerA: UIViewController  {

    override func viewDidLoad() {
        super.viewDidLoad()
    }

    //MARK:Passing Data through Navigation PushViewController
    @IBAction func goToViewControllerB(_ sender: Any) {

        if let viewControllerB = UIStoryboard(name: "Main", bundle: nil).instantiateViewController(withIdentifier: "ViewControllerB") as? ViewControllerB {
            viewControllerB.isSomethingEnabled = true
            if let navigator = navigationController {
                navigator.pushViewController(viewControllerB, animated: true)
            }
        }
    }
}

ViewControllerB

import UIKit

class ViewControllerB: UIViewController {

    //MARK:  - Variable for Passing Data through Navigation push   
    var isSomethingEnabled = false

    override func viewDidLoad() {
        super.viewDidLoad()
        //Print value received through navigation push
        print("Value of 'isSomethingEnabled' from ViewControllerA : ", isSomethingEnabled)
    }
}

Passing Data through Segue : From ViewControllerA to ViewControllerB

Step 1. Create Segue from ViewControllerA to ViewControllerB and give Identifier = showDetailSegue in Storyboard as shown below

enter image description here

Step 2. In ViewControllerB Declare a viable named isSomethingEnabled and print its value.

Step 3. In ViewControllerA pass isSomethingEnabled's value while passing Segue

So Here is the complete code for :

ViewControllerA

import UIKit

class ViewControllerA: UIViewController  {

    override func viewDidLoad() {
        super.viewDidLoad()
    }

    //MARK:  - - Passing Data through Segue  - - 
    @IBAction func goToViewControllerBUsingSegue(_ sender: Any) {
        performSegue(withIdentifier: "showDetailSegue", sender: nil)
    }

    //Segue Delegate Method
    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        if (segue.identifier == "showDetailSegue") {
            let controller = segue.destination as? ViewControllerB
            controller?.isSomethingEnabled = true//passing data
        }
    }
}

ViewControllerB

import UIKit

class ViewControllerB: UIViewController {
    var isSomethingEnabled = false

    override func viewDidLoad() {
        super.viewDidLoad()
        //Print value received through segue
        print("Value of 'isSomethingEnabled' from ViewControllerA : ", isSomethingEnabled)
    }
}

Passing Data through Delegate : From ViewControllerB to ViewControllerA

Step 1. Declare Protocol ViewControllerBDelegate in ViewControllerB file but outside the class

protocol ViewControllerBDelegate: NSObjectProtocol {

    // Classes that adopt this protocol MUST define
    // this method -- and hopefully do something in
    // that definition.
    func addItemViewController(_ controller: ViewControllerB?, didFinishEnteringItem item: String?)
}

Step 2. Declare Delegate variable instance in ViewControllerB

var delegate: ViewControllerBDelegate?

Step 3. Send data for delegate inside viewDidLoad method of ViewControllerB

delegate?.addItemViewController(self, didFinishEnteringItem: "Data for ViewControllerA")

Step 4. Confirm ViewControllerBDelegate in ViewControllerA

class ViewControllerA: UIViewController, ViewControllerBDelegate  {
// to do
}

Step 5. Confirm that you will implement delegate in ViewControllerA

if let viewControllerB = UIStoryboard(name: "Main", bundle: nil).instantiateViewController(withIdentifier: "ViewControllerB") as? ViewControllerB {
            viewControllerB.delegate = self//confirming delegate
            if let navigator = navigationController {
                navigator.pushViewController(viewControllerB, animated: true)
            }
        }

Step 6. Implement delegate method for receiving data in ViewControllerA

func addItemViewController(_ controller: ViewControllerB?, didFinishEnteringItem item: String?) {
        print("Value from ViewControllerB's Delegate", item!)
    }

So Here is the complete code for :

ViewControllerA

import UIKit

class ViewControllerA: UIViewController, ViewControllerBDelegate  {

    override func viewDidLoad() {
        super.viewDidLoad()
    }

    //Delegate method
    func addItemViewController(_ controller: ViewControllerB?, didFinishEnteringItem item: String?) {
        print("Value from ViewControllerB's Delegate", item!)
    }

    @IBAction func goToViewControllerForDelegate(_ sender: Any) {

        if let viewControllerB = UIStoryboard(name: "Main", bundle: nil).instantiateViewController(withIdentifier: "ViewControllerB") as? ViewControllerB {
            viewControllerB.delegate = self
            if let navigator = navigationController {
                navigator.pushViewController(viewControllerB, animated: true)
            }
        }
    }
}

ViewControllerB

import UIKit

//Protocol decleare
protocol ViewControllerBDelegate: NSObjectProtocol {
    // Classes that adopt this protocol MUST define
    // this method -- and hopefully do something in
    // that definition.
    func addItemViewController(_ controller: ViewControllerB?, didFinishEnteringItem item: String?)
}

class ViewControllerB: UIViewController {
    var delegate: ViewControllerBDelegate?

    override func viewDidLoad() {
        super.viewDidLoad()
        //MARK:  - - - -  Set Data for Passing Data through Delegate  - - - - - -
        delegate?.addItemViewController(self, didFinishEnteringItem: "Data for ViewControllerA")
    }
}

Passing Data through Notification Observer : From ViewControllerB to ViewControllerA

Step 1. Set and Post data in Notification observer in ViewControllerB

let objToBeSent = "Test Message from Notification"
        NotificationCenter.default.post(name: Notification.Name("NotificationIdentifier"), object: objToBeSent)

Step 2. Add Notification Observer in ViewControllerA

NotificationCenter.default.addObserver(self, selector: #selector(self.methodOfReceivedNotification(notification:)), name: Notification.Name("NotificationIdentifier"), object: nil)

Step 3. Receive Notification data value in ViewControllerA

@objc func methodOfReceivedNotification(notification: Notification) {
        print("Value of notification : ", notification.object ?? "")
    }

So Here is the complete code for :

ViewControllerA

import UIKit

class ViewControllerA: UIViewController{

    override func viewDidLoad() {
        super.viewDidLoad()

        // add observer in controller(s) where you want to receive data
        NotificationCenter.default.addObserver(self, selector: #selector(self.methodOfReceivedNotification(notification:)), name: Notification.Name("NotificationIdentifier"), object: nil)
    }

    //MARK: Method for receiving Data through Post Notification 
    @objc func methodOfReceivedNotification(notification: Notification) {
        print("Value of notification : ", notification.object ?? "")
    }
}

ViewControllerB

import UIKit

class ViewControllerB: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()

        //MARK:Set data for Passing Data through Post Notification
        let objToBeSent = "Test Message from Notification"
        NotificationCenter.default.post(name: Notification.Name("NotificationIdentifier"), object: objToBeSent)
    }
}

Passing Data through Block : From ViewControllerB to ViewControllerA

Step 1. Declare block in ViewControllerB

var authorizationCompletionBlock:((Bool)->())? = {_ in}

Step 2. Set data in block in ViewControllerB

if authorizationCompletionBlock != nil
        {
            authorizationCompletionBlock!(true)
        }

Step 3. Receive block data in ViewControllerA

//Receiver Block
                controller!.authorizationCompletionBlock = { isGranted in
                    print("Data received from Block is :", isGranted)
                }

So Here is the complete code for :

ViewControllerA

import UIKit

class ViewControllerA: UIViewController  {

    override func viewDidLoad() {
        super.viewDidLoad()
    }

    //MARK:Method for receiving Data through Block
        override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
            if (segue.identifier == "showDetailSegue") {
                let controller = segue.destination as? ViewControllerB
                controller?.isSomethingEnabled = true

                //Receiver Block
                controller!.authorizationCompletionBlock = { isGranted in
                    print("Data received from Block is :", isGranted)
                }
            }
        }
}

ViewControllerB

import UIKit

class ViewControllerB: UIViewController {

    //MARK:Variable for Passing Data through Block
    var authorizationCompletionBlock:((Bool)->())? = {_ in}

    override func viewDidLoad() {
        super.viewDidLoad()

        //MARK:Set data for Passing Data through Block
        if authorizationCompletionBlock != nil
        {
            authorizationCompletionBlock!(true)
        }
    }
}

You can find complete sample Application at my GitHub Please let me know if you have any question(s) on this.

@Christopher Wade Cantley 2015-08-25 15:28:28

I know this is a beaten subject but for those looking to answer this question with a SWIFT slant and want a bare-bones example, here my go-to method for passing data if you are using a segue to get around.

It is similar to the above but without the buttons, labels and such. Just simply passing data from one view to the next.

Setup The Storyboard

There are three parts.

  1. The Sender
  2. The Segue
  3. The Receiver

This is a very simple view layout with a segue between them.


Very simple view layout.  Note : No navigation controller


Here is the setup for the sender


The Sender


Here is the setup for the receiver.


The Receiver


Lastly, the setup for the segue.


The Segue Identifier


The View Controllers

We are keeping this simple so no buttons, not actions, we are simply moving data from the sender to the receiver when the application loads and then outputting the transmitted value to the console.

This page takes the initially loaded value and passes it along.

import UIKit


class ViewControllerSender: UIViewController {

    // THE STUFF - put some info into a variable
    let favoriteMovie = "Ghost Busters"

    override func viewDidAppear(animated: Bool) {
        // PASS IDENTIFIER - go to the recieving view controller.
        self.performSegueWithIdentifier("goToReciever", sender: self)
    }

    override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {

        //GET REFERENCE - ...to the receiver view.
        var viewControllerReceiver = segue.destinationViewController as? ViewControllerReceiver

        //PASS STUFF - pass the variable along to the target.
        viewControllerReceiver!.yourFavMovie = self.favoriteMovie

    }

}

This page just sends the value of the variable to the console when it loads. By this point, our favorite movie should be in that variable.

import UIKit

class ViewControllerReceiver: UIViewController {

    //Basic empty variable waiting for you to pass in your fantastic favorite movie.
    var yourFavMovie = ""

    override func viewDidLoad() {
        super.viewDidLoad()

        //And now we can view it in the console.
        println("The Movie is \(self.yourFavMovie)")

    }   
}

That is how you can tackle it if you want to use a segue and you don't have your pages under a navigation controller.

Once it is run it should switch to the receiver view automatically and pass the value from the sender to the receiver, displaying the value in the console.

Ghost Busters is a classic folks.

@Matt Price 2012-03-16 11:39:33

This question seems to be very popular here on stackoverflow so I thought I would try and give a better answer to help out people starting in the world of iOS like me.

I hope this answer is clear enough for people to understand and that I have not missed anything.

Passing Data Forward

Passing data forward to a view controller from another view controller. You would use this method if you wanted to pass an object/value from one view controller to another view controller that you may be pushing on to a navigation stack.

For this example, we will have ViewControllerA and ViewControllerB

To pass a BOOL value from ViewControllerA to ViewControllerB we would do the following.

  1. in ViewControllerB.h create a property for the BOOL

    @property (nonatomic, assign) BOOL isSomethingEnabled;
    
  2. in ViewControllerA you need to tell it about ViewControllerB so use an

    #import "ViewControllerB.h"
    

    Then where you want to load the view eg. didSelectRowAtIndex or some IBAction you need to set the property in ViewControllerB before you push it onto nav stack.

    ViewControllerB *viewControllerB = [[ViewControllerB alloc] initWithNib:@"ViewControllerB" bundle:nil];
    viewControllerB.isSomethingEnabled = YES;
    [self pushViewController:viewControllerB animated:YES];
    

    This will set isSomethingEnabled in ViewControllerB to BOOL value YES.

Passing Data Forward using Segues

If you are using Storyboards you are most likely using segues and will need this procedure to pass data forward. This is similar to the above but instead of passing the data before you push the view controller, you use a method called

-(void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender

So to pass a BOOL from ViewControllerA to ViewControllerB we would do the following:

  1. in ViewControllerB.h create a property for the BOOL

    @property (nonatomic, assign) BOOL isSomethingEnabled;
    
  2. in ViewControllerA you need to tell it about ViewControllerB so use an

    #import "ViewControllerB.h"
    
  3. Create a the segue from ViewControllerA to ViewControllerB on the storyboard and give it an identifier, in this example we'll call it "showDetailSegue"

  4. Next, we need to add the method to ViewControllerA that is called when any segue is performed, because of this we need to detect which segue was called and then do something. In our example we will check for "showDetailSegue" and if that's performed we will pass our BOOL value to ViewControllerB

    -(void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender{
        if([segue.identifier isEqualToString:@"showDetailSegue"]){
            ViewControllerB *controller = (ViewControllerB *)segue.destinationViewController;
            controller.isSomethingEnabled = YES;
        }
    }
    

    If you have your views embedded in a navigation controller you need to change the method above slightly to the following

    -(void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender{
        if([segue.identifier isEqualToString:@"showDetailSegue"]){
            UINavigationController *navController = (UINavigationController *)segue.destinationViewController;
            ViewControllerB *controller = (ViewControllerB *)navController.topViewController;
            controller.isSomethingEnabled = YES;
        }
    }
    

    This will set isSomethingEnabled in ViewControllerB to BOOL value YES.

Passing Data Back

To pass data back from ViewControllerB to ViewControllerA you need to use Protocols and Delegates or Blocks, the latter can be used as a loosely coupled mechanism for callbacks.

To do this we will make ViewControllerA a delegate of ViewControllerB. This allows ViewControllerB to send a message back to ViewControllerA enabling us to send data back.

For ViewControllerA to be a delegate of ViewControllerB it must conform to ViewControllerB's protocol which we have to specify. This tells ViewControllerA which methods it must implement.

  1. In ViewControllerB.h, below the #import, but above @interface you specify the protocol.

    @class ViewControllerB;
    
    @protocol ViewControllerBDelegate <NSObject>
    - (void)addItemViewController:(ViewControllerB *)controller didFinishEnteringItem:(NSString *)item;
    @end
    
  2. next still in the ViewControllerB.h you need to setup a delegate property and synthesize in ViewControllerB.m

    @property (nonatomic, weak) id <ViewControllerBDelegate> delegate;
    
  3. In ViewControllerB we call a message on the delegate when we pop the view controller.

    NSString *itemToPassBack = @"Pass this value back to ViewControllerA";
    [self.delegate addItemViewController:self didFinishEnteringItem:itemToPassBack];
    
  4. That's it for ViewControllerB. Now in ViewControllerA.h, tell ViewControllerA to import ViewControllerB and conform to its protocol.

    #import "ViewControllerB.h"
    
    @interface ViewControllerA : UIViewController <ViewControllerBDelegate>
    
  5. In ViewControllerA.m implement the following method from our protocol

    - (void)addItemViewController:(ViewControllerB *)controller didFinishEnteringItem:(NSString *)item
    {
        NSLog(@"This was returned from ViewControllerB %@",item);
    }
    
  6. Before pushing viewControllerB to navigation stack we need to tell ViewControllerB that ViewControllerA is its delegate, otherwise we will get an error.

    ViewControllerB *viewControllerB = [[ViewControllerB alloc] initWithNib:@"ViewControllerB" bundle:nil];
    viewControllerB.delegate = self
    [[self navigationController] pushViewController:viewControllerB animated:YES];
    

References

  1. Using Delegation to Communicate With Other View Controllers in the View Controller Programming Guide
  2. Delegate Pattern

NSNotification center It's another way to pass data.

// add observer in controller(s) where you want to receive data
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(handleDeepLinking:) name:@"handleDeepLinking" object:nil];

-(void) handleDeepLinking:(NSNotification *) notification {
    id someObject = notification.object // some custom object that was passed with notification fire.
}

// post notification
id someObject;
[NSNotificationCenter.defaultCenter postNotificationName:@"handleDeepLinking" object:someObject];

Passing Data back from one class to another (A class can be any controller, Network/session manager, UIView subclass or any other class)

Blocks are anonymous functions.

This example passes data from Controller B to Controller A

define a block

@property void(^selectedVoucherBlock)(NSString *); // in ContollerA.h

add block handler (listener) where you need a value (for example you need your API response in ControllerA or you need ContorllerB data on A)

// in ContollerA.m

- (void)viewDidLoad {
    [super viewDidLoad];
    __unsafe_unretained typeof(self) weakSelf = self;
    self.selectedVoucherBlock = ^(NSString *voucher) {
        weakSelf->someLabel.text = voucher;
    };
}

Go to Controller B

UIStoryboard *storyboard = [UIStoryboard storyboardWithName:@"Main" bundle:nil];
ControllerB *vc = [storyboard instantiateViewControllerWithIdentifier:@"ControllerB"];
vc.sourceVC = self;
    [self.navigationController pushViewController:vc animated:NO];

fire block

-(void)tableView:(UITableView *)tableView didSelectRowAtIndexPath: 
(NSIndexPath *)indexPath {
    NSString *voucher = vouchersArray[indexPath.row];
    if (sourceVC.selectVoucherBlock) {
        sourceVC.selectVoucherBlock(voucher);
    }
    [self.navigationController popToViewController:sourceVC animated:YES];
}

Another Working Example for Blocks

@alan-p 2012-08-30 13:16:17

Do we also have to put an @class ViewControllerB; above the @protocol definition? Without it I get an "Expected type" error on ViewControllerB in the line: - (void)addItemViewController:(ViewControllerB *)controller didFinishEnteringItem:(NSString *)item; within the @protocol declaration

@Andrew Davis 2012-11-22 11:11:30

This works great. As alan-p says, don't forget to write @class ViewControllerB; above the protocol otherwise you'll receive "Expected a type" error.

@Melvin Roest 2012-12-24 14:25:13

I had a problem with specifying the protocols. I also had the [at]class error, but it also didn't accept the @interface ViewControllerA : UIViewController <ViewControllerBDelegate> line. If you also have this problem (to tell ViewControllerA to conform to the protocol), then click the link here. I used the answer of the user Anomie. link

@पवन 2013-01-29 10:20:52

Everything is awesome except some typos like [email protected]"ViewControllerB" bundle=nil]

@carmen_munich 2013-06-18 14:23:28

Passing Data Forward using Segue's (4.) first one works also for views which are embedded in a navigation controller.

@Max 2013-08-13 13:45:27

@Matt Price :- If we specify a class method in viewControllerB and then return the required string from that method, then can't this approach substitute the delegate method or is there any drawback to using class method ?

@Matt Price 2013-08-13 16:53:15

@Max I'm not 100% sure, as i'm still learning myself. However i'd say that what you suggest would make classes tightly coupled.

@DoS 2013-09-06 17:48:29

@Max class methods are really meant to be used as "helper" methods. essentially just a way to quickly do some routine task or get some info about the class. if you look through the apple documentation at the nsstring class, that is a perfect example of its use. essentially "hey class, give me back something useful i can use."

@malhal 2013-09-27 03:30:40

you don't need delegates for passing back, just use unwind.

@Michael Graff 2014-03-07 14:46:16

IMHO, as soon as you start passing things around in complicated ways, I think of two things. One, you better have a great testing framework... And two, I'd consider using notifications.

@uplearnedu.com 2014-03-28 21:21:27

When I put "viewControllerB.delegate = self;" in ViewControllerB I'm getting an error. Assigning to 'id<ViewControllerBDelegate>' from incompatible type 'ViewControllerB *const __strong', I'm not sure what I'm doing wrong. Can anyone help? Plus I had to change: initWithNib --> initWithNibName.

@nmokkary 2014-04-26 10:08:44

for Passing Data back using Segue's, i think step 6 must change. can you please show me the solution?

@S.J 2014-05-30 16:08:19

@MattPrice please tell why not use the same "forward data method" to pass data back.

@Matt Price 2014-05-30 22:13:07

@S.J I'm no expert but, you would have to keep reference to ViewControllerA in ViewControllerB in order to set the property on ViewControllerA. This makes the views tightly coupled which is bad practice IMO.

@Nazir 2014-06-05 05:26:59

if you are using NavigationController you have to use [self.navigationController pushViewController:viewController animated:YES]; instead [self pushViewController:viewControllerB animated:YES];

@Xcoder 2014-10-02 05:48:26

Just a question, but to pass data back why can't we just use prepareForSegue again?

@nhgrif 2015-11-12 00:39:46

It's probably worth mentioning that data can be passed backward via unwind segues.

@Honey 2016-04-14 14:20:45

Forward means from A->B Back means B->A, but be able to do back as well, you must import viewControllerB.h into viewControllerA as well and that is bad practice!

@fishinear 2017-04-30 11:21:38

@Honey, no it isn't bad practice. Here B is on a lower level then A. That is, A knows about B, but B does not know about A. A needs to know about B anyways, because he needs to push B onto the stack.

@Timur Bernikovich 2019-02-06 09:08:07

I prefer to make it without delegates and segues. It can be done with custom init or by setting optional values.

1. Custom init

class ViewControllerA: UIViewController {
  func openViewControllerB() {
    let viewController = ViewControllerB(string: "Blabla", completionClosure: { success in
      print(success)
    })
    navigationController?.pushViewController(animated: true)
  }
}

class ViewControllerB: UIViewController {
  private let completionClosure: ((Bool) -> Void)
  init(string: String, completionClosure: ((Bool) -> Void)) {
    self.completionClosure = completionClosure
    super.init(nibName: nil, bundle: nil)
    title = string
  }

  func finishWork() {
    completionClosure()
  }
}

2. Optional vars

class ViewControllerA: UIViewController {
  func openViewControllerB() {
    let viewController = ViewControllerB()
    viewController.string = "Blabla"
    viewController.completionClosure = { success in
      print(success)
    }
    navigationController?.pushViewController(animated: true)
  }
}

class ViewControllerB: UIViewController {
  var string: String? {
    didSet {
      title = string
    }
  }
  var completionClosure: ((Bool) -> Void)?

  func finishWork() {
    completionClosure?()
  }
}

@Sachin Rasane 2018-11-13 10:28:59

USING NOTIFICATION CENTER

For Swift 3

let imageDataDict:[String: UIImage] = ["image": image]

  // post a notification
  NotificationCenter.default.post(name: NSNotification.Name(rawValue: "notificationName"), object: nil, userInfo: imageDataDict) 
  // `default` is now a property, not a method call

 // Register to receive notification in your class
 NotificationCenter.default.addObserver(self, selector: #selector(self.showSpinningWheel(_:)), name: NSNotification.Name(rawValue: "notificationName"), object: nil)

 // handle notification
 func showSpinningWheel(_ notification: NSNotification) {
        print(notification.userInfo ?? "")
        if let dict = notification.userInfo as NSDictionary? {
            if let id = dict["image"] as? UIImage{
                // do something with your image
            }
        }
 }

For Swift 4

let imageDataDict:[String: UIImage] = ["image": image]

  // post a notification
  NotificationCenter.default.post(name: NSNotification.Name(rawValue: "notificationName"), object: nil, userInfo: imageDataDict) 
  // `default` is now a property, not a method call

 // Register to receive notification in your class
 NotificationCenter.default.addObserver(self, selector: #selector(self.showSpinningWheel(_:)), name: NSNotification.Name(rawValue: "notificationName"), object: nil)

 // handle notification
 @objc func showSpinningWheel(_ notification: NSNotification) {
        print(notification.userInfo ?? "")
        if let dict = notification.userInfo as NSDictionary? {
            if let id = dict["image"] as? UIImage{
                // do something with your image
            }
        }
 }

@Leo Dabus 2019-02-10 19:08:50

You were supposed to drop the NS prefix of NSNotificationand most of the types and since Swift 3. Same applies to use Swift native Dictionary [AnyHashable: Any] instead of NSDictionary. Btw stackoverflow.com/questions/30328452/…

@Nayab Khan 2018-05-07 15:32:11

well we have few ways we can work with delegates system or using storyboardSegue

1- As working with setter and getter method like in viewController.h
   @property (retain, nonatomic) NSString *str;
   now, in viewController.m
   @synthesize str;


   here i have pdf url and segue to another viewController like this and pdfObject is my pdfModel basicilly is NSOBJECT class.  

   str =[NSString stringWithFormat:@"%@",pdfObject.objPath];
NSLog(@"pdfUrl :***: %@ :***:",pdfUrl);

[self performSegueWithIdentifier:@"programPDFViewController_segue" sender:self];

pragma mark - Navigation

  // In a storyboard-based application, you will often want to do a little preparation before navigation

 - (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {

    if ([[segue identifier] isEqualToString:@"programPDFViewController_segue"]){
    programPDFViewController *pdfVC = [segue destinationViewController];
    [pdfVC setRecievedPdfUrl:str];

   }
 }

Now successfully i received my pdf url string and other ViewController and use that string in webview...

2- As working with delegates like this i have one NSObject class of utilities containing my methods of dateFormatter , sharedInstance, EscapeWhiteSpaceCharacters, convertImageToGrayScale and more method i worked with through out the application so now in utilities.h

in this you dont need to create variables on evering time parsing data from one to another view controller one time your created string variable in utilities.h just make it nil; and used again

  @interface Utilities : NSObject

  Utilities.h
 +(Utilities*)sharedInstance;

 @property(nonatomic,retain)NSString* strUrl;

now in utilities.m

   @implementation utilities


  +(utilities*)sharedInstance
  {
  static utilities* sharedObj = nil;
  if (sharedObj == nil) {
    sharedObj = [[utilities alloc] init];
    }
   return sharedObj;
  }

now its done come to your firstViewController.m and call delegate

NSString*str =[NSString stringWithFormat:@"%@",pdfObject.objPath];

[Connection sharedInstance].strUrl=nil;
[Connection sharedInstance].strUrl=str;

 Now go to you secondViewController.m directly use it without creating variable 

 in viewwillapear what i did

 -(void)viewWillAppear:(BOOL)animated{
     [super viewWillAppear:YES];

   [self webViewMethod:[Connection sharedInstance].strUrl];

 }


 -(void)WebViewMethod:(NSString)Url{

 // working with webview enjoy coding :D

 }

this delegate work is reliable with memory management

@Kamani Jasmin 2018-03-23 10:30:42

There are 3 types for passing data one ViewController to another ViewController.

  1. Programatically
  2. Segue
  3. UserDefaults

Demo Project Link Here - https://github.com/kamanijasmin13/Swift-Pass-data-between-viewcontrollers

Programatically enter image description here

Segue enter image description here

UserDefaults enter image description here

Demo Project Link Here - https://github.com/kamanijasmin13/Swift-Pass-data-between-viewcontrollers

@Parth Barot 2018-04-12 10:17:20

You can create push segue from source viewcontroller to destination viewcontroller and give identifier name like below. enter image description here

You have to performsegue from didselectRowAt like this.

func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
    performSegue(withIdentifier: "segue", sender: self)
}

And you can pass the array of selected item from the below function.

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
    let index = CategorytableView.indexPathForSelectedRow
    let indexNumber = index?.row
    print(indexNumber!)
    let VC = segue.destination as! AddTransactionVC
   VC.val = CategoryData[indexNumber!] . //You can pass here entire array instead of array element.

}

And you have to check the value in viewdidload of destination viewcontroller and then store it into the database.

override func viewDidLoad{
 if val != ""{
        btnSelectCategory.setTitle(val, for: .normal)
    }
}

@Shahin 2018-03-26 15:49:44

You have to always follow MVC concept when creating apps for iOS. There are two scenarios where you may want to pass data from a ViewController to another:

  1. When there is an "A" ViewContoller in the hierarchy and you want to send some data to "B" which is the next viewcontroller. In this case you have to use Segue. Just set an identifier for the segue and then in the "A" VC, write the following code:

    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        if segue.identifier == "A to B segue identifier" {
            let bViewController = segue.destination as! UIDocumentBrowserViewController
            bViewController.data = someData
        }
    }
    
  2. When there is an A which opened B upon itself as modal (or embed). Now the B viewcontroller should be blind about it's parent. So the best way to send data back to A is to use Delegation. Create a delegate protocol in the B viewcontroller and a delegate property. So B will report (send data back) to it's delegate. In the A viewcontroller, we implement the B viewcontroller's delegate protocol and will set self as the delegate property of B viewcontroller in prepare(forSegue:) method.

This is how it should be implemented correctly. Hope it helps

@Jason Cross 2015-04-05 22:04:57

There is some good information in many of the answers given, but none address the question fully.

The question asks about passing information between view controllers. The specific example given asks about passing information between views, but given the self-stated newness to iOS, the original poster likely meant between viewControllers, not between views (without any involvement from the ViewControllers). It seems that all the answers focus on two view controllers, but what if the app evolves to need to involve more than two view controllers in the information exchange?

The original poster also asked about Singletons and the use of the AppDelegate. These questions need to be answered.

To help anyone else looking at this question, who wants a full answer, I'm going to attempt to provide it.

Application Scenarios

Rather than having a highly hypothetical, abstract discussion, it helps to have concrete applications in mind. To help define a two-view-controller situation and a more-than-two-view-controller situation, I am going to define two concrete application scenarios.

Scenario one: maximum two view controllers ever need to share information. See diagram one.

diagram of original problem

There are two view controllers in the application. There is a ViewControllerA (Data Entry Form), and View Controller B (Product List). The items selected in the product list must match the items displayed in the text box in the data entry form. In this scenario, ViewControllerA and ViewControllerB must communicate directly with each other and no other view controllers.

Scenario two: more than two view controllers need to share the same information. See diagram two.

home inventory application diagram

There are four view controllers in the application. It is a tab-based application for managing home inventory. Three view controllers present differently filtered views of the same data:

  • ViewControllerA - Luxury Items
  • ViewControllerB - Non-insured Items
  • ViewControllerC - Entire Home Inventory
  • ViewControllerD - Add New Item Form

Any time an individual item is created or edited, it must also synchronize with the other view controllers. For example, if we add a boat in ViewControllerD, but it is not yet insured, then the boat must appear when the user goes to ViewControllerA (Luxury Items), and also ViewControllerC (Entire Home Inventory), but not when the user goes to ViewControllerB (Non-insured Items). We need be concerned with not only adding new items, but also deleting items (which may be allowed from any of the four view controllers), or editing existing items (which may be allowed from the "Add New Item Form", repurposing the same for editing).

Since all the view controllers do need to share the same data, all four view controllers need to remain in synchronization, and therefore there needs to be some sort of communication to all other view controllers, whenever any single view controller changes the underlying data. It should be fairly obvious that we do not want each view controller communicating directly with each other view controller in this scenario. In case it is not obvious, consider if we had 20 different view controllers (rather than just 4). How difficult and error-prone would it be to notify each of the other 19 view controllers any time one view controller made a change?

The Solutions: Delegates and the Observer Pattern, and Singletons

In scenario one, we have several viable solutions, as other answers have given

  • segues
  • delegates
  • setting properties on view controllers directly
  • NSUserDefaults (actually a poor choice)

In scenario two, we have other viable solutions:

  • Observer Pattern
  • Singletons

A singleton is an instance of a class, that instance being the only instance in existence during its lifetime. A singleton gets its name from the fact that it is the single instance. Normally developers who use singletons have special class methods for accessing them.

+ (HouseholdInventoryManager*) sharedManager; {
    static dispatch_once_t onceQueue;
    static HouseholdInventoryManager* _sharedInstance;

    // dispatch_once is guaranteed to only be executed once in the
    // lifetime of the application
    dispatch_once(&onceQueue, ^{
        _sharedInstance = [[self alloc] init];
    });
    return _sharedInstance;
}

Now that we understand what a singleton is, let's discuss how a singleton fits into the observer pattern. The observer pattern is used for one object to respond to changes by another object. In the second scenario, we have four different view controllers, who all want to know about changes to the underlying data. The "underlying data" should belong to a single instance, a singleton. The "know about changes" is accomplished by observing changes made to the singleton.

The home inventory application would have a single instance of a class which is designed to manage a list of inventory items. The manager would manage a collection of household items. The following is a class definition for the data manager:

#import <Foundation/Foundation.h>

@class JGCHouseholdInventoryItem;

@interface HouseholdInventoryManager : NSObject
/*!
 The global singleton for accessing application data
 */
+ (HouseholdInventoryManager*) sharedManager;


- (NSArray *) entireHouseholdInventory;
- (NSArray *) luxuryItems;
- (NSArray *) nonInsuredItems;

- (void) addHouseholdItemToHomeInventory:(JGCHouseholdInventoryItem*)item;
- (void) editHouseholdItemInHomeInventory:(JGCHouseholdInventoryItem*)item;
- (void) deleteHoueholdItemFromHomeInventory:(JGCHouseholdInventoryItem*)item;
@end

When the collection of home inventory items changes, the view controllers need to be made aware of this change. The class definition above does not make it obvious how this will happen. We need to follow the observer pattern. The view controllers must formally observe the sharedManager. There are two ways to observe another object:

  • Key-Value-Observing (KVO)
  • NSNotificationCenter.

In scenario two, we do not have a single property of the HouseholdInventoryManager which could be observed using KVO. Because we do not have a single property which is easily observable, the observer pattern, in this case, must be implemented using NSNotificationCenter. Each of the four view controllers would subscribe to notifications, and the sharedManager would send notifications to the notification center when appropriate. The inventory manager does not need to know anything about the view controllers or instances of any other classes which may be interested in knowing when the collection of inventory items changes; the NSNotificationCenter takes care of these implementation details. The View Controllers simply subscribe to notifications, and the data manager simply posts notifications.

Many beginner programmers take advantage of the fact that there is always exactly one Application Delegate in the lifetime of the application, which is globally accessible. Beginning programmers use this fact to stuff objects and functionality into the appDelegate as a convenience for access from anywhere else in the application. Just because the AppDelegate is a singleton doesn't mean it should replace all other singletons. This is a poor practice as it places too much burden on one class, breaking good object-oriented practices. Each class should have a clear role that is easily explained, often just by the name of the class.

Any time your Application Delegate starts to get bloated, start to remove functionality into singletons. For example, the Core Data Stack should not be left in the AppDelegate, but should instead be put in its own class, a coreDataManager class.

References

@Korey Hinton 2015-01-29 17:35:29

There are tons of ways to do this and it's important to pick the right one. Probably one of the biggest architectural decisions lies on how the model code will be shared or accessed throughout the app.

I wrote a blog post about this a while back: Sharing Model Code. Here's a brief summary:

Shared data

One approach is to share pointers to the model objects between view controllers.

  • Brute force iteration on view controllers (in Navigation or Tab Bar Controller) to set the data
  • Set data in prepareForSegue (if storyboards) or init (if programmatic)

Since prepare for segue is the most common here is an example:

override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
    var next = segue.destinationViewController as NextViewController
    next.dataSource = dataSource
}

Independent access

Another approach is to handle a screen full of data at a time and instead of coupling the view controllers to each other couple each view controller to single data source that they can get to independently.

The most common way I've seen this done is a singleton instance. So if your singleton object was DataAccess you could do the following in the viewDidLoad method of UIViewController:

func viewDidLoad() {
    super.viewDidLoad()
    var data = dataAccess.requestData()
}

There are addition tools that also help pass along data:

  • Key-Value Observing
  • NSNotification
  • Core Data
  • NSFetchedResultsController
  • Data Source

Core Data

The nice thing about Core Data is that it has inverse relationships. So if you want to just give a NotesViewController the notes object you can because it'll have an inverse relationship to something else like the notebook. If you need data on the notebook in the NotesViewController you can walk back up the object graph by doing the following:

let notebookName = note.notebook.name

Read more about this in my blog post: Sharing Model Code

@Suragch 2015-08-11 06:35:25

Swift

There are tons and tons of explanations here and around StackOverflow, but if you are a beginner just trying to get something basic to work, try watching this YouTube tutorial (It's what helped me to finally understand how to do it).

Passing data forward to the next View Controller

The following is an example based on the video. The idea is to pass a string from the text field in the First View Controller to the label in the Second View Controller.

enter image description here

Create the storyboard layout in the Interface Builder. To make the segue, you just Control click on the button and drag over to the Second View Controller.

First View Controller

The code for the First View Controller is

import UIKit

class FirstViewController: UIViewController {

    @IBOutlet weak var textField: UITextField!

    // This function is called before the segue
    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {

        // get a reference to the second view controller
        let secondViewController = segue.destination as! SecondViewController

        // set a variable in the second view controller with the String to pass
        secondViewController.receivedString = textField.text!
    }

}

Second View Controller

And the code for the Second View Controller is

import UIKit

class SecondViewController: UIViewController {

    @IBOutlet weak var label: UILabel!

    // This variable will hold the data being passed from the First View Controller
    var receivedString = ""

    override func viewDidLoad() {
        super.viewDidLoad()

        // Used the text from the First View Controller to set the label
        label.text = receivedString
    }

}

Don't forget

  • Hook up the outlets for the UITextField and the UILabel.
  • Set the first and second View Controllers to the appropriate Swift files in IB.

Passing data back to the previous View Controller

To pass data back from the second view controller to the first view controller, you use a protocol and a delegate. This video is a very clear walk though of that process:

The following is an example based on the video (with a few modifications).

enter image description here

Create the storyboard layout in the Interface Builder. Again, to make the segue, you just Control drag from the button to the Second View Controller. Set the segue identifier to showSecondViewController. Also, don't forget to hook up the outlets and actions using the names in the following code.

First View Controller

The code for the First View Controller is

import UIKit

class FirstViewController: UIViewController, DataEnteredDelegate {

    @IBOutlet weak var label: UILabel!

    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        if segue.identifier == "showSecondViewController" {
            let secondViewController = segue.destination as! SecondViewController
            secondViewController.delegate = self
        }
    }

    func userDidEnterInformation(info: String) {
        label.text = info
    }
}

Note the use of our custom DataEnteredDelegate protocol.

Second View Controller and Protocol

The code for the second view controller is

import UIKit

// protocol used for sending data back
protocol DataEnteredDelegate: class {
    func userDidEnterInformation(info: String)
}

class SecondViewController: UIViewController {

    // making this a weak variable so that it won't create a strong reference cycle
    weak var delegate: DataEnteredDelegate? = nil

    @IBOutlet weak var textField: UITextField!

    @IBAction func sendTextBackButton(sender: AnyObject) {

        // call this method on whichever class implements our delegate protocol
        delegate?.userDidEnterInformation(info: textField.text!)

        // go back to the previous view controller
        _ = self.navigationController?.popViewController(animated: true)
    }
}

Note that the protocol is outside of the View Controller class.

That's it. Running the app now you should be able to send data back from the second view controller to the first.

@piofusco 2015-12-08 07:35:05

Given some of the latest Swift updates, is this still a common pattern to implement?

@Suragch 2015-12-08 11:23:51

Most all of the Swift updates that I've seen have been relatively minor syntactical changes, not changes in how data is passed between view controllers. If I do learn of any major changes like that, I'll update my answer.

@Mixaz 2016-04-01 15:51:13

offtopic - iOS has such an ugly way to pass parameters to new view controllers, unbelievable - you have to set parameters not in a place when you're making the call, but in some other one. Android has a better approach in this regard - when you start an Activity you can pass any data (well, almost) via its starting Intent. Easy. No need to cast or something. Passing return values back to caller is an essential thing too, no need to delegate. Of course it is possible to use ugly approaches too, no problem there ))

@Himanshu jamnani 2016-07-30 11:37:14

@suragch : how to pass data in same case when we are not using segue??

@Suragch 2016-07-30 15:26:18

@Himanshu, first get a reference to the second view controller. Then update the public variable that it contains.

@Honey 2016-09-25 19:26:08

I watched the video over and over. Still very confused about 'which class is delegating to which class'. To my understanding (similar to a tableView that doesn't know its number of sections) viewController doesn't know what it's label's text should be. So it delegates it secondViewController. So inside secondviewController we should have viewcontroller.delegate = self. But in this moment of the video it's exactly the opposite. Where am I getting it wrong?

@Suragch 2016-09-26 06:44:20

@Honey. I think the word "delegate" is confusing. Let me use the word "worker". The "worker" (first view controller) does whatever the "boss" (second view controller) tells it to do. The "boss" doesn't know who its "worker" will be; it could be anyone. So in the first view controller ("worker" class), it says, I will be your "worker". You tell me what to write in the label and I'll do it for you. Thus, secondViewController.delegate = self means "I agree to be the boss's worker." See this answer for another example and more explanation.

@Caleb 2018-08-31 12:42:14

It should be said that you don't actually need the whole protocol/delegate dance just to pass information between view controllers. View controllers are just objects, and they can refer to each other and send messages to each other just like other objects. We use delegation to avoid creating a dependency between the two classes, so that your code is easier to change and reuse later. Saying "here's how you do it" without explaining why you do it that way and when you don't need to bother makes it all seem a lot more confusing than it needs to be.

@Suragch 2018-08-31 13:33:40

@Caleb, good point. Thanks. I don't actually know the "when you don't need to bother" part. In production code do you sometimes just do direct communication? In what circumstances?

@Caleb 2018-08-31 14:57:27

@Suragch You don't need it if you use a different approach, such as using a data model (see my answer). You don't need it if you don't mind having a two-way dependency between the classes (there's often one-way dependency anyway, since the parent controller often instantiates the child). You don't need to create a specific protocol if you add a standardized communication method to all your view controllers.

@Suragch 2018-09-01 00:40:34

@Caleb, I reread your answer and understand it better than the first time I read it. I see how updating the data model directly would make it so that you don't need to pass data between view controllers. About the two-way dependency, in addition to making reusability more difficult, isn't there also a danger of a memory leak? About the standardized communication method, what is that? That sounds interesting.

@Caleb 2018-09-01 02:16:38

@Suragch two-way dependency: I just mean that each class knows about the other. It doesn't mean that they both need strong references to each other, so no danger of a retain cycle. standardized method: Lots of possibilities here, but basically the idea is just to make sure that all your view controllers communicate with each other in a common way. For example, you could use KVC to get and set values in the child view controller. There are still dependencies here, because VC's need to know something about what values they can get and set, but there's still some abstraction there.

@soorej babu 2016-07-07 12:59:33

Simpler way is here.

Just use of global variable. Declare the object or variable needed to pass to the next class.

For example, we have 2 classes - classA and classB respectively.

In classA normally contains:

#import "classA.h"

@interface classA()

@end

@implementation classA

-(void)viewDidLoad
{
    ...
}
-(void)didReceiveMemoryWarning
{
    ...
}

and classB contains:

#import "classB.h"

@interface classB()

@end

@implementation classB

-(void)viewWillLoad
{
    ...
}
-(void)didReceiveMemoryWarning
{
    ...
}

Now, import the second class classB to classA

#import "classA.h"
#import "classB.h"  //---import classB to classA.
@interface classA()

@end

@implementation classA

-(void)viewDidLoad
{
    ...
}
-(void)didReceiveMemoryWarning
{
    ...
}

Now we have a bridge to go to the second class classB now, for declaring a variable or object as global, declare it in the .m file of first class as below

In classA.h

#import "classA.h"
#import "classB.h"
@interface classA()

@end
NSString *temp;  //----declare any object/variable as global.
@implementation classA

-(void)viewDidLoad
{
    ...
    [email protected]"Hello";
    ...
}
-(void)didReceiveMemoryWarning
{
    ...
}

Here the object temp is global object of class NSString for accessing the global object or variable in any class, just redeclare the object or variable in the second class. Eg. given below:

In classB.m

#import "classB.h"

@interface classB()

@end
extern NSString *temp;  //----use `extern` keyword for using the global object/variable in classB that was declared in classA.
@implementation classB

-(void)viewDidLoad
{
    ...
    LabeL.text=temp;
    ...
}
-(void)didReceiveMemoryWarning
{
    ...
}

Now the value can be accessed by the second class. Simple!.. This method can be followed for any number of classes.

Note:

You should import .h file of second class to the first class. But no need to import the .h file of first class to second class.

Remember the bridge, if there is a bridge it should be able to go on both sides.

I think this will help. It helped me when i was in the same situation.

@tf.alves 2016-08-31 10:17:16

This is a dangerous method! You should (almost) never be using global variables! You should instead use delegates and segue preparation methods in order to inject information in your viewcontrollers

@soorej babu 2016-09-16 04:44:33

but still i didn't got any problems on this method or any kind of loss of data

@tf.alves 2016-09-16 08:00:36

I believe in you. Sometimes is not a matter of working vs not working, but making your development as safe as it can be. The way you are building this, you are left with a variable in memory for as long as your application lives, instead of using it and then discarding it when no longer needed.

@GeneCode 2017-06-09 01:18:15

Global variable is dangerous because you could have used another local variable with same name and it would mess up the project.

@soorej babu 2017-06-12 07:08:16

@GeneCode its all about coding standard. A good programmer never gives identical name for different variables (whatever it be, global or local).

@GeneCode 2017-06-13 01:13:24

For a small project it is easy to say. If you're involved in a very big project, like 50+ viewcontrollers then you'll regret making a global variable. For a small project it is ok I guess.

@soorej babu 2017-06-14 07:13:24

I worked single handled on an iOS seller app for an e-commerce website having 37 viewcontrollers. and i used the global variable thing that i explained above. and it didn't affected my app in any sort of performance, memory or other issues. and it uses a maximum of 5 images in that project. till it works smoothly even in iphone 4 and 4s.

@Umair 2017-05-08 22:54:50

I recommend blocks/closures and custom constructors.

Suppose you have to pass string from FirstViewController to SecondViewController.

Your First View Controller.

class FirstViewController : UIViewController {

    func moveToViewControllerB() {

        let second_screen = SecondViewController.screen(string: "DATA TO PASS", call_back: {
            [weak self] (updated_data) in
            ///This closure will be called by second view controller when it updates something
        })
        self.navigationController?.pushViewController(second_screen, animated: true)
    }


}

Your Second View Controller

class SecondViewController : UIViewController {

    var incoming_string : String?
    var call_back : ((String) -> Void)?

    class func screen(string: String?, call_back : ((String) -> Void)?) -> SecondViewController {

        let me = SecondViewController(nibName: String(describing: self), bundle: Bundle.main);
        me.incoming_string = string
        me.call_back = call_back
        return me
    }

    // Suppose its called when you have to update FirstViewController with new data.
    func updatedSomething() {

        //Executing block that is implemented/assigned by the FirstViewController.
        self.call_back?("UPDATED DATA")
    }

}

@Yevgeni 2014-04-11 00:33:01

Passing data back from ViewController 2(destination) to viewController 1(Source) is the more interesting thing. Assuming you use storyBoard those are all the ways i found out:

  • Delegate
  • Notification
  • User defaults
  • Singleton

Those were discussed here already.

I found there are more ways:

-Using Block callbacks:

use it in the prepareForSegue method in the VC1

NextViewController *destinationVC = (NextViewController *) segue.destinationViewController;
[destinationVC setDidFinishUsingBlockCallback:^(NextViewController *destinationVC)
{
    self.blockLabel.text = destination.blockTextField.text;
}];

-Using storyboards Unwind (Exit)

Implement a method with a UIStoryboardSegue argument in VC 1, like this one:

-(IBAction)UnWindDone:(UIStoryboardSegue *)segue { }

In the storyBoard hook the "return" button to the green Exit button(Unwind) of the vc. Now you have a segue that "goes back" so u can use the destinationViewController property in the prepareForSegue of VC2 and change any property of VC1 before it goes back.

  • Another option of using storyboards Undwind (Exit) - you can use the method you wrote in VC1

    -(IBAction)UnWindDone:(UIStoryboardSegue *)segue {
        NextViewController *nextViewController = segue.sourceViewController;
        self.unwindLabel.text = nextViewController.unwindPropertyPass;
    } 
    

    And in the prepareForSegue of VC1 you can change any property you want to share.

In both unwind options you can set the tag property of the button and check it in the prepareForSegue.

Hope i added something to the discussion.

:) Cheers.

@Anubrata Santra 2013-09-27 10:38:36

There are multiple methods for sharing data.

  1. You can always share data using NSUserDefaults. Set the value you want to share with respect to a key of your choice and get the value from NSUserDefault associated to that key in the next view controller.

    [[NSUserDefaults standardUserDefaults] setValue:value forKey:key]
    [[NSUserDefaults standardUserDefaults] objectForKey:key]
    
  2. You can just create a property in viewcontrollerA. Create an object of viewcontrollerA in viewcontrollerB and assign the desired value to that property.

  3. You can also create custom delegates for this.

@José González 2014-05-17 07:00:51

The typical purpose of NSUserDefaults is to store user preferences that persist between app executions, so anything stored here will stay here unless explicitly removed. It's a really bad idea to use this to pass information between view controllers (or any other objects) in an app.

@Matteo Manferdini 2016-12-03 15:27:48

There are many answers to this questions offering many different ways to perform view controller communication that would indeed work, but I don't see anywhere mentioned which one are actually best to use and which ones to avoid.

In practice, in my opinion only a few solutions are recommended:

  • To pass data forward:
    • override the prepare(for:sender:) method of UIViewController when using a storyboard and segues
    • pass data through an initializer or through properties when performing view controller transitions thtough code
  • To pass data backwards
    • update the app shared state (which you can pass forward between view controllers with either one of the methods above)
    • use delegation
    • use an unwind segue

Solutions I recommend NOT to use:

  • Referencing the previous controller directly instead of using delegation
  • Sharing data through a singleton
  • Passing data through the app delegate
  • Sharing data through the user defaults
  • Passing data through notifications

These solutions, although working in the short term, introduce too many dependencies that will garble the architecture of the app and create more problems later.

For those interested, I wrote some articles that address these points more in depth and highlight the various drawbacks:

@Caleb 2011-03-06 13:49:13

The M in MVC is for "Model" and in the MVC paradigm the role of model classes is to manage a program's data. A model is the opposite of a view -- a view knows how to display data, but it knows nothing about what to do with data, whereas a model knows everything about how to work with data, but nothing about how to display it. Models can be complicated, but they don't have to be -- the model for your app might be as simple as an array of strings or dictionaries.

The role of a controller is to mediate between view and model. Therefore, they need a reference to one or more view objects and one or more model objects. Let's say that your model is an array of dictionaries, with each dictionary representing one row in your table. The root view for your app displays that table, and it might be responsible for loading the array from a file. When the user decides to add a new row to the table, they tap some button and your controller creates a new (mutable) dictionary and adds it to the array. In order to fill in the row, the controller creates a detail view controller and gives it the new dictionary. The detail view controller fills in the dictionary and returns. The dictionary is already part of the model, so nothing else needs to happen.

@ak_tyagi 2015-05-29 12:34:45

You can save data in App delegate to access it across view controllers in your application. All you have to do is create a shared instance of app delegate

AppDelegate *appDelegate = (AppDelegate *)[UIApplication sharedApplication].delegate;

For Example

if you declare a NSArray object *arrayXYZ then you can access it in any view controller by appDelegate.arrayXYZ

@Hai Feng Kao 2016-08-19 18:36:25

It is the method-of-choice for hackathon

@AsifHabib 2013-07-27 08:52:34

I was searching this solution for long time, Atlast I found it. First of all declare all the objects in your SecondViewController.h file like

@interface SecondViewController: UIviewController 
{
    NSMutableArray *myAray;
    CustomObject *object;
}

Now in your implementation file allocate the memory for those objects like this

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
     self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
     if (self) 
     {
         // Custom initialization
         myAray=[[NSMutableArray alloc] init];
         object=[[CustomObject alloc] init];
     }
     return self;
}

Now you have allocated the memory for Array and object. now you can fill that memory before pushing this ViewController

Go to your SecondViewController.h and write two methods

-(void)setMyArray:(NSArray *)_myArray;
-(void)setMyObject:(CustomObject *)_myObject;

in implementation file you can implement the function

-(void)setMyArray:(NSArray *)_myArray
{
     [myArra addObjectsFromArray:_myArray];
}
-(void)setMyObject:(CustomObject *)_myObject
{
     [object setCustomObject:_myObject];
}

expecting that your CustomObject must have a setter function with it.

now your basic work is done. go to the place where you want to push the SecondViewController and do the following stuff

SecondViewController *secondView= [[SecondViewController alloc] initWithNibName:@"SecondViewController " bundle:[NSBundle MainBundle]] ;
[secondView setMyArray:ArrayToPass];
[secondView setMyObject:objectToPass];
[self.navigationController pushViewController:secondView animated:YES ];

Take care for spelling mistakes.

@tmac_balla 2015-12-22 03:13:41

An Apple way to do this is to use Segues. You need to use prepareForSegue() function

There are lots of great tutorials around, here is one: https://www.iphonelife.com/content/unleash-your-inner-app-developer-part-21-passing-data-between-controllers

Also, read up the Apple docs on using segues: https://developer.apple.com/library/ios/featuredarticles/ViewControllerPGforiPhoneOS/UsingSegues.html

@Dalvik 2015-11-28 06:55:29

to send the data from one VC to other use this simple approach:

YourNextVC *nxtScr = (YourNextVC*)[self.storyboard  instantiateViewControllerWithIdentifier:@"YourNextVC"];//Set this identifier from your storyboard

nxtScr.comingFrom = @"PreviousScreen"l
[self.navigationController nxtScr animated:YES];

@Ashok R 2016-08-11 07:21:42

do i have to create comingFrom property on my YourNextVC ViewController?

@Dalvik 2016-08-11 08:32:01

@Ashok yes you have to create comingFrom in your YourNextVC.h like @property (strong,nonatomic) NSString *comingFrom;

@crazy_tiger_corp 2015-09-28 09:00:00

This is a really great tutorial for anyone that wants one. Here is the example code:

- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
    if ([segue.identifier isEqualToString:@"myIdentifer]) {
        NSIndexPath *indexPath = [self.tableView indexPathForSelectedRow];
        myViewController *destViewController = segue.destinationViewController;
        destViewController.name = [object objectAtIndex:indexPath.row];
    }
}

@krushnsinh 2015-05-27 14:11:49

if you wants to pass data from ViewControlerOne to ViewControllerTwo try these..

do these in ViewControlerOne.h

 @property (nonatomic, strong) NSString *str1;

do these in ViewControllerTwo.h

 @property (nonatomic, strong) NSString *str2;

Synthesize str2 in ViewControllerTwo.m

@interface ViewControllerTwo ()
@end
@implementation ViewControllerTwo
@synthesize str2;

do these in ViewControlerOne.m

 - (void)viewDidLoad
 {
   [super viewDidLoad];

  // Data or string you wants to pass in ViewControllerTwo..
  self.str1 = @"hello world";

 }

on the buttons click event do this..

-(IBAction)ButtonClicked
{ //Navigation on buttons click event from ViewControlerOne to ViewControlerTwo with transferring data or string..
  ViewControllerTwo *objViewTwo=[self.storyboard instantiateViewControllerWithIdentifier:@"ViewControllerTwo"];
  obj.str2=str1;
  [self.navigationController pushViewController: objViewTwo animated:YES];
}

do these in ViewControllerTwo.m

- (void)viewDidLoad
{
 [super viewDidLoad];
  NSLog(@"%@",str2);
}

@user2998756 2013-11-18 12:48:24

If you want to pass data from one controller to other try this code

FirstViewController.h

@property (nonatomic, retain) NSString *str;

SecondViewController.h

@property (nonatomic, retain) NSString *str1;

FirstViewController.m

- (void)viewDidLoad
   {
     // message for the second SecondViewController
     self.str = @"text message";

     [super viewDidLoad];
   }

-(IBAction)ButtonClicked
 {
   SecondViewController *secondViewController = [[SecondViewController alloc] initWithNibName:@"SecondViewController" bundle:nil];
   secondViewController.str1 = str;
  [self.navigationController pushViewController:secondViewController animated:YES];
 }

@borncrazy 2014-04-08 10:24:29

There are various ways by which a data can be received to a different class in iOS. For example -

  1. Direct initialization after the allocation of another class.
  2. Delegation - for passing data back
  3. Notification - for broadcasting data to multiple classes at a single time
  4. Saving in NSUserDefaults - for accessing it later
  5. Singleton classes
  6. Databases and other storage mechanisms like plist, etc.

But for the simple scenario of passing a value to a different class whose allocation is done in the current class, the most common and preferred method would be the direct setting of values after allocation. This is done as follows:-

We can understand it using two controllers - Controller1 and Controller2

Suppose in Controller1 class you want to create the Controller2 object and push it with a String value being passed. This can be done as this:-

- (void)pushToController2 {

    Controller2 *obj = [[Controller2 alloc] initWithNib:@"Controller2" bundle:nil];
    [obj passValue:@"String"];
    [self pushViewController:obj animated:YES];
}

In the implementation of the Controller2 class there will be this function as-

@interface Controller2  : NSObject

@property (nonatomic , strong) NSString* stringPassed;

@end

@implementation Controller2

@synthesize stringPassed = _stringPassed;

- (void) passValue:(NSString *)value {

    _stringPassed = value; //or self.stringPassed = value
}

@end

You can also directly set the properties of the Controller2 class in the similar way as this:

- (void)pushToController2 {

    Controller2 *obj = [[Controller2 alloc] initWithNib:@"Controller2" bundle:nil];
    [obj setStringPassed:@"String"];  
    [self pushViewController:obj animated:YES];
}

To pass multiple values you can use the multiple parameters like :-

Controller2 *obj = [[Controller2 alloc] initWithNib:@"Controller2" bundle:nil];
[obj passValue:@“String1” andValues:objArray withDate:date]; 

Or if you need to pass more than 3 parameters which are related to a common feature you can store the values to a Model class and pass that modelObject to the next class

ModelClass *modelObject = [[ModelClass alloc] init]; 
modelObject.property1 = _property1;
modelObject.property2 = _property2;
modelObject.property3 = _property3;

Controller2 *obj = [[Controller2 alloc] initWithNib:@"Controller2" bundle:nil];
[obj passmodel: modelObject];

So in-short if you want to -

1) set the private variables of the second class initialise the values by calling a custom function and passing the values.
2) setProperties do it by directlyInitialising it using the setter method.
3) pass more that 3-4 values related to each other in some manner , then create a model class and set values to its object and pass the object using any of the above process.

Hope this helps

@App Dev Guy 2015-01-16 03:18:43

I have seen a lot of people over complicating this using the didSelectRowAtPath method. I am using Core Data in my example.

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath{

    //this solution is for using Core Data
    YourCDEntityName * value = (YourCDEntityName *)[[self fetchedResultsController] objectAtIndexPath: indexPath];

    YourSecondViewController * details = [self.storyboard instantiateViewControllerWithIdentifier:@"nameOfYourSecondVC"];//make sure in storyboards you give your second VC an identifier

    //Make sure you declare your value in the second view controller
    details.selectedValue = value;

    //Now that you have said to pass value all you need to do is change views
    [self.navigationController pushViewController: details animated:YES];

}

4 lines of code inside the method and you are done.

@user2563044 2014-09-16 17:18:29

I am currently contributing to an open source solution to this problem through a project called MCViewFactory, which may be found here:

https://github.com/YetiHQ/manticore-iosviewfactory

The idea is imitate Android's intent paradigm, using a global factory to manage which view you are looking at and using "intents" to switch and pass data between views. All the documentation is on the github page, but here are some highlights:

You setup all your views in .XIB files and register them in the app delegate, while initializing the factory.

// Register activities

MCViewFactory *factory = [MCViewFactory sharedFactory];

// the following two lines are optional. 
[factory registerView:@"YourSectionViewController"]; 

Now, in your VC, anytime you want to move to a new VC and pass data, you create a new intent and add data to its dictionary (savedInstanceState). Then, just set the current intent of factory:

MCIntent* intent = [MCIntent intentWithSectionName:@"YourSectionViewController"];
[intent setAnimationStyle:UIViewAnimationOptionTransitionFlipFromLeft];
[[intent savedInstanceState] setObject:@"someValue" forKey:@"yourKey"];
[[intent savedInstanceState] setObject:@"anotherValue" forKey:@"anotherKey"];
// ...
[[MCViewModel sharedModel] setCurrentSection:intent];

All of your views that conform to this need to be subclasses of MCViewController, which allow you to override the new onResume: method, allowing you access to the data you've passed in.

-(void)onResume:(MCIntent *)intent {
    NSObject* someValue = [intent.savedInstanceState objectForKey:@"yourKey"];
    NSObject* anotherValue = [intent.savedInstanceState objectForKey:@"anotherKey"];

    // ...

    // ensure the following line is called, especially for MCSectionViewController
    [super onResume:intent];
}

Hope some of you find this solution useful/interesting.

@Itachi 2017-08-16 03:53:57

Then all the controller objects could get/set all the registered dictionaries in any scopes? Downvote this.

@Boda Taljo 2014-09-01 19:46:45

This is not the way to do it, you should use delegates, I'll assume we have two view controllers ViewController1 and ViewController2 and this check thing is in the first one and when its state changes, you want to do something in ViewController2, to achieve that in the proper way, you should do the below:

Add a new file to your project (Objective-C Protocol) File -> New, now name it ViewController1Delegate or whatever you want and write these between the @interface and @end directives

@optional

- (void)checkStateDidChange:(BOOL)checked;

Now go to ViewController2.h and add

#import "ViewController1Delegate.h"

then change its definition to

@interface ViewController2: UIViewController<ViewController1Delegate>

Now go to ViewController2.m and inside the implementation add:

- (void)checkStateDidChange:(BOOL)checked {
     if (checked) {
           // Do whatever you want here
           NSLog(@"Checked");
     }
     else {
           // Also do whatever you want here
           NSLog(@"Not checked");
     }
}

Now go to ViewController1.h and add the following property:

@property (weak, nonatomic) id<ViewController1Delegate> delegate; 

Now if you are creating ViewController1 inside ViewController2 after some event, then you should do it this way using NIB files:

ViewController1* controller = [[NSBundle mainBundle] loadNibNamed:@"ViewController1" owner:self options:nil][0];
controller.delegate = self;
[self presentViewController:controller animated:YES completion:nil];

Now you are all set, whenever you detect the event of check changed in ViewController1, all you have to do is the below

[delegate checkStateDidChange:checked]; // You pass here YES or NO based on the check state of your control

Please tell me if there's anything that's not clear of if I didn't understand your question properly.

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