CODEWITHSUNDEEP
iphoneobjective-cxcode
user559142
user559142

Reputation: 12517

Pass data from child view to parent view - iPhone

I have two controller classes A and B. A instantiates several of B. When the appropriate button is pressed in A, A instantiates a B and program flow is passed to B. At the end of B's run I want it to pass some data back to A. How is this possible?

To be more precise, I have an NSArray of Objects, which I would like to return to 'A' after B runs its last method...

Upvotes: 1

Views: 1225

Answers (3)

Joe McMahon
Joe McMahon

Reputation: 3382

As Ray says, there are a number of ways, but the simplest is to pass an instance of A as an argument to B's initializer, and then just call A.whatever(...) to pass the data back. It's probably easiest to define and use the whatever(...) method as an informal protocol - you know it exists, and the two modules know it exists, but there's nothing specific in the code that requires it to exist.

If you want to have a way of declaring that B will need an object to call back to and to specify what that object must be able to do, you could set up a formal protocol. This would say that you will need an object, not necessarily an A, but any object, that conforms to MyBCallbackProtocol, which you define as needing to have the one instance method of whatever(...). The formal protocol lets the compiler check that the object you pass in definitely supports the method call you want.

It's probably overkill for this situation - but if the communication between A and B becomes more complex, you might want to use it to be sure that you've implemented all the methods that you've decided you need. If A is changed, the protocol helps to ensure that B will still be able to pass back its information.

NSNotificationCenter may be overkill as well if A and B are very specific to your app. It does, however, completely isolate B while allowing others to get data from it; if B is meant to be a reusable utility class, it's worth considering.

I would not pass in a reference to an ivar in A; this is getting B way too involved in A's business.

Upvotes: 1

Bjarne Mogstad
Bjarne Mogstad

Reputation: 1154

There is a few way to accomplish that, the easiest and fastest solution is to use NSNotificationCenter. With NSNotificationCenter you can subscribe and send custom notifications.

NSNotificationCenter: Receive

[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(didFinishParsing:) name:@"yourNoticationName" object:nil];
- (void)didFinishParsing:(NSNotification *)aNotification {...}

Send

NSDictionary *userInfo = [NSDictionary dictionaryWithObjectsAndKeys:@"some", @"optional", @"data", @":)" nil];
[[NSNotificationCenter defaultCenter] postNotificationName:@"yourNoticationName" object:nil userInfo:userInfo];

Upvotes: 0

Rayfleck
Rayfleck

Reputation: 12106

Lots of options:

  1. Keep your data in a singleton DataManager object that both VCs can reference
  2. Have B post an NSNotification that it is done, and have A be an observer for that notification, pass the data of interest in the notification.
  3. Give B a reference to an iVar in A so it can directly set the values
  4. Give B a reference to a method in A (possibly by declaring a protocol) so it can call that method and pass the data base that way.

Probably more, but these are the ones I use most often.

Upvotes: 3

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