Pass data back to previous viewcontroller

I am trying to pass data BACK TO previous viewController.

Does anyone know how to pass data back from ViewController B to ViewController A? So I want a string to go 'from' BIDAddTypeOfDealViewController to BIDDCCreateViewController. A user edits viewController B and I want that edited data back in ViewController A where I then use it.

I am using the 'passing data back' section of this answer. How mine differs: Point 3 and 6 just mentions when views are popped so I have put that code in viewWillDisappear. I think that is correct? Also on Point 6 I did not initialise with nib as that is old. I'm using storyboards. And I did not add that last line as I do not believe I would have to push it. Pressing a button on my storyboard already takes me forward.

I think the problem may arise in BIDDCCreateViewController, I have the method but I cannot run it. To run a method it should go [self method]. I am unable to do that. Well that is just what I am guessing.

It compiles and runs fine just nothing is logged, so I don't know if it works.

UPDATE: I am unable to get the 'sendDataToA' method to execute.

#import <UIKit/UIKit.h>
#import "BIDAddTypeOfDealViewController.h"
 
 @interface BIDDCCreateViewController : UIViewController
 @property (strong, nonatomic) NSString *placeId;
- (IBAction)gotoBViewController:(id)sender;
@end


#import "BIDDCCreateViewController.h"
#import "BIDAddTypeOfDealViewController.h"

@implementation BIDDCCreateViewController

- (void)viewDidLoad
{
    [super viewDidLoad];
	// Do any additional setup after loading the view.
    NSLog(@"SUCCESSFULLY PASSED PLACE ID: %@", self.placeId);
}

-(void)sendDataToA:(NSString *)myStringData
{
    
    NSLog(@"Inside sendDataToA");
    UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Your string Data Showing" message:myStringData delegate:self cancelButtonTitle:@"Ok " otherButtonTitles:nil];
    [alert show];
}

- (IBAction)gotoBViewController:(id)sender {
    NSLog(@"pressed");
    BIDAddTypeOfDealViewController *bidAddType = [[BIDAddTypeOfDealViewController alloc]init];
    bidAddType.delegate = self;
    
}
@end


@protocol senddataProtocol <NSObject>
-(void)sendDataToA:(NSString *)myStringData;
@end

#import <UIKit/UIKit.h>
@interface BIDAddTypeOfDealViewController : UIViewController <UITextFieldDelegate>//Using this delegate for data a user inputs
@property(nonatomic,assign)id delegate;
//other textfield outlets not relevant
- (IBAction)chooseDiscountDeal:(id)sender;
@end

#import "BIDAddTypeOfDealViewController.h"

@interface BIDAddTypeOfDealViewController ()

@end

@implementation BIDAddTypeOfDealViewController
@synthesize delegate;

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

- (void)viewDidLoad
{
    [super viewDidLoad];
}

-(void)viewWillDisappear:(BOOL)animated
{
    [delegate sendDataToA:@"Apple"];
}
@end

You can use a delegate. So in your ViewController B you need to create a protocol that sends data back to your ViewController A. Your ViewController A would become a delegate of ViewController B.

If you are new to objective C, please look at What is Delegate.

Create protocol in ViewControllerB.h :

#import <UIKit/UIKit.h>

@protocol senddataProtocol <NSObject>

-(void)sendDataToA:(NSArray *)array; //I am thinking my data is NSArray, you can use another object for store your information. 

@end

@interface ViewControllerB : UIViewController

@property(nonatomic,assign)id delegate;

ViewControllerB.m

@synthesize delegate;
-(void)viewWillDisappear:(BOOL)animated
{
     [delegate sendDataToA:yourdata];

}

in your ViewControllerA : when you go to ViewControllerB

ViewControllerA *acontollerobject=[[ViewControllerA alloc] initWithNibName:@"ViewControllerA" bundle:nil];
acontollerobject.delegate=self; // protocol listener
[self.navigationController pushViewController:acontollerobject animated:YES];

and define your function:

-(void)sendDataToA:(NSArray *)array
{
   // data will come here inside of ViewControllerA
}

Edited :

You can See this example : How you can Pass data back to previous viewcontroller: Tutorial link

A shorter and simpler method than protocol/delegate is to create a closure:

For sending a String back in my case. In ViewControllerA:

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
    if let viewControllerB = segue.destination as? ViewControllerB {
        viewControllerB.callback = { message in
            //Do what you want in here!
        }
    }
}

In ViewControllerB:

var callback : ((String) -> Void)?

@IBAction func done(sender: AnyObject) {
    callback?("Hi")
    self.dismiss(animated: true, completion: nil)
}

Swift: Sending data back using the delegate pattern

My full answer that covers passing data both ways is here. My answer explaining the delegate pattern is here.

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:

• YouTube tutorial: iOS Swift Basics Tutorial: Protocols and Delegates. But also read this post to make sure you don't get into a strong reference cycle.

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

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 prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
        if segue.identifier == "showSecondViewController" {
            let secondViewController = segue.destinationViewController 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: UIButton) {
        
        // call this method on whichever class implements our delegate protocol
        delegate?.userDidEnterInformation(textField.text!)
        
        // go back to the previous view controller
        self.navigationController?.popViewControllerAnimated(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.

Edit: Use @Erhan's solution above. Not this one. This is not a good solution.

This will help. Write this in your ViewControllerB.

    // Get array of current navigation stack
    NSArray *arrayViewControllers = [self.navigationController viewControllers];
    
    // Get previous viewController object from it
    YOUR_VIEW_CONTROLLER_NAME *objViewController = (YOUR_VIEW_CONTROLLER_NAME *)[arrayViewControllers objectAtIndex:arrayViewControllers.count-2];

    // For safety this check is needed. whether it the class that you want or not.
    if ([objViewController isKindOfClass:[YOUR_VIEW_CONTROLLER_NAME class]])
    {
        // Access properties of YOUR_VIEW_CONTROLLER_NAME here
        objViewController.yourProperty = YOUR_VALUE;
    }

As Erhan Demirci answered, you can use delegates. Delegates are helpful when you want to pass data to a single view controller.

NSNotificationCenter is another convenient way to transfer data between viewcontrollers/objects. This is very helpful in broadcasting data within the application.

read documentation here.

Custom delegate is the best option to move data but you can try this also.

You can use NSUserDefaults for Moving the data any where you want.

Swift 3 Code

UserDefaults.standard.set(<Value>, forKey: <Key>) 
// To set data
        
UserDefaults.standard.object(forKey: <Key>) 
// To get data

You can also use NSNotification for move data.

NotificationCenter.default.post(name: Notification.Name(rawValue: "refresh"), object: myDict) 

NotificationCenter.default.addObserver(self, selector: #selector(refreshList(_:)), name: NSNotification.Name(rawValue: "refresh"), object: nil)

There is protocol there is closure. With closure, we need to avoid memory leaks by using weak self (or unowned self). With protocol, there would be one per viewController that you want to "monitor", end up with dozens of delegate to implement. Here I've another simple solutions in Swift:

Inside a new file or existing one (for example: UIViewController+Extensions.swift), create this protocol:

protocol ViewControllerBackDelegate: class {
	func back(from viewController: UIViewController)
}

Inside LEVEL-2 viewController, where you want a callback when Back is pressed from:

class LevelTwoViewController: UIViewController {
	// making this a weak variable so that it won't create a strong reference cycle
	weak var delegate: ViewControllerBackDelegate? = nil

	override func willMove(toParentViewController parent: UIViewController?) {
		super.willMove(toParentViewController: parent)
		if (parent == nil) {
			delegate?.back(from: self)
		}
	}
}

Since delegate is optional, you may add this code to a base class of your view controllers. I would add to where it needs to be.

In your LEVEL-1 viewController, assume you calling LEVEL-2 via a segue in Storyboard:

class LevelOneViewController: UIViewController {
	override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
		if (segue.identifier == "Go to Level 2") {
			if let vc = segue.destination as? LevelTwoViewController {
				vc.selectedItems = self.selectedItems // passing data-in
				vc.delegate = self
			}
		}
        // repeat `if` for another sub-level view controller
    }
}

extension LevelOneViewController: ViewControllerBackDelegate {    
	func back(from viewController: UIViewController) {
		if let vc = viewController as? LevelTwoViewController {
			self.selectedItems = vc.selectedItems
			// call update if necessary
		}
        // repeat `if` for another sub-level view controller
	}
}

• only one protocol is required.
• only one extension per first-level viewController.
• no modifications to sub-level viewController if more/less data need to return
• handle data-out just like data-in in prepare(for:sender:)

//FirstViewController

import UIKit

class FirstViewController: UIViewController {

override func viewDidLoad() {
    super.viewDidLoad()
    // Do any additional setup after loading the view, typically from a nib.
}
override func viewWillAppear(_ animated: Bool) {
     
}

@IBAction func pushToSecond(_ sender: Any) {
    if let vc = storyboard?.instantiateViewController(withIdentifier: "SecondViewController")as? SecondViewController {
         vc.callBack = { (id: String,name: String,age: Int) in
            print(id,name,age)
        }
        self.navigationController?.pushViewController(vc, animated: true)
    }
}

}

// //SecondViewController

import UIKit

class SecondViewController: UIViewController {

var callBack: ((_ id: String, _ name: String, _ age: Int)-> Void)?

@IBAction func BackToFirstWitData(_ sender: Any) {
    
    callBack?("1","Test",22)
    self.navigationController?.popViewController(animated: true)
    
}
override func viewDidLoad() {
    super.viewDidLoad()
    
    // Do any additional setup after loading the view.
}

}

Here is how I would do it.

@interface ViewControllerA:UIViewController
@property(strong, nonatomic) ViewControllerB * recieverB;
@end

@implementation ViewControllerA
//implement class
- (void)prepareForSegue:(UIStoryboardSegue *) sender:(id)sender
{
segue.destinationViewController.recieverA = self;
}
-(void)viewDidLoad
{
//stop strong refrence cycle
self.viewControllerB = nil;
}
@end

Class B

@interface ViewControllerB:UIViewController
@property(strong, nonatomic, getter = parentClass) ViewControllerB * recieverA;
@end

@implementation ViewControllerB
//implement class
- (void)viewWillDisappear:(BOOL)animated
{
parentClass.recieverB = self;
//now class A will have an instance on class b
}
@end

I didn't put the #import