Passing Data between View Controllers

Question

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?

Answer 1

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.

Answer 2

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.

Answer 3

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.

Answer 4

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

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.

Answer 5

NewsViewController

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
  [tbl_View deselectRowAtIndexPath:indexPath animated:YES];
  News *newsObj = [newstitleArr objectAtIndex:indexPath.row];
  NewsDetailViewController *newsDetailView = [[NewsDetailViewController alloc] initWithNibName:@"NewsDetailViewController" bundle:nil];

  newsDetailView.newsHeadlineStr = newsObj.newsHeadline;

  [self.navigationController pushViewController:newsDetailView animated:YES];
}

NewsDetailViewController.h

@interface NewsDetailViewController : UIViewController
@property(nonatomic,retain) NSString *newsHeadlineStr;
@end

NewsDetailViewController.m

@synthesize newsHeadlineStr;

Answer 6

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