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

If you want to send data from one to another viewController, here's a way to it:

Say we have viewControllers: viewControllerA and viewControllerB

Now in viewControllerB.h

@interface viewControllerB : UIViewController {

  NSString *string;
  NSArray *array;

}

- (id)initWithArray:(NSArray)a andString:(NSString)s;

In viewControllerB.m

#import "viewControllerB.h"

@implementation viewControllerB

- (id)initWithArray:(NSArray)a andString:(NSString)s {

   array = [[NSArray alloc] init];
   array = a;

   string = [[NSString alloc] init];
   string = s;

}

In viewControllerA.m

#import "viewControllerA.h"
#import "viewControllerB.h"

@implementation viewControllerA

- (void)someMethod {

  someArray = [NSArray arrayWithObjects:@"One", @"Two", @"Three", nil];
  someString = [NSString stringWithFormat:@"Hahahahaha"];

  viewControllerB *vc = [[viewControllerB alloc] initWithArray:someArray andString:someString];

  [self.navigationController pushViewController:vc animated:YES];
  [vc release];

}

So this is how you can pass data from viewControllerA to viewControllerB without setting any delegate. ;)

Answer 2

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

Answer 3

Passing Data between FirstViewController to SecondViewController as below

For example:

FirstViewController String value as

StrFirstValue = @"first";

so we can pass this value in second class using below step

1>We need to crate string object in SecondViewController.h file

NSString *strValue;

2>Need to declare property as below below declaration in .h file

@property (strong, nonatomic)  NSString *strSecondValue;

3>Need synthesize that value in FirstViewController.m file below header declaration

@synthesize strValue;

and in FirstViewController.h :

@property (strong, nonatomic)  NSString *strValue;

4>In FirstViewController,From which method we navigate to second view please write below code in that method.

SecondViewController *secondView= [[SecondViewController alloc]     
initWithNibName:@"SecondViewController " bundle:[NSBundle MainBundle]];

[secondView setStrSecondValue:StrFirstValue];

[self.navigationController pushViewController:secondView animated:YES ];

Answer 4

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];
 }

Answer 5

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.

---

---

Here is the setup for the sender

---

---

Here is the setup for the receiver.

---

---

Lastly, the setup for the segue.

---

---

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.

Answer 6

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