How to properly pass NSArray / NSMutableArray from one UIViewController to another ...

Question

An iphone app I'm working on is terminating periodically ... and I have a feeling it is because of how I'm accessing a shared NSArray amongst several view controllers. So ...

What is the best way to pass NSArray/NSMutableArray amongst several ViewControllers ... all of which can modify and/or set it to nil or whatever?

Thanks

Answer 1

you are probably not retaining it, it gets deallocated and you are trying to access it again. try to send a [myArray retain] where you are using it (in each of the controllers), and [myArray release] when you are done with it

Answer 2

There are two approaches, generally speaking.

In the first approach, when you instantiate your next view controller, you could set an array property to "inherit" from the current (soon-to-be previous or parent) view controller:

MyNextViewController *_myNextViewController = [[MyNextViewController alloc] initWithNibName:@"MyNextViewController" bundle:nil];
_myNextViewController.myViewControllerArray = self.myViewControllerArray;
...

In the second approach, you could create a myAppDelegateArray property in your application delegate, instantiating the array when the application initializes (or instantiated somewhere else, on demand).

You can then call the getter for this property from any class — including view controllers.

For example, within an instance of MyNextViewController, you might have a property called myViewControllerArray and you would set it as follows:

self.myViewControllerArray = [UIAppDelegate myAppDelegateArray]; 

You would add a #define statement somewhere in your application constants file, e.g.:

#define UIAppDelegate ((MyAppDelegate *)[UIApplication sharedApplication].delegate)

or use the full [UIApplication sharedApplication].delegate call, if you prefer.

As a general approach, people seem to prefer the app delegate approach, as it decentralizes access to the desired property.

With this approach, if you rearrange your view controllers or insert new view controllers into your VC hierarchy, you wouldn't need to debug child view controller properties inherited from parent view controllers, because a reference is always available from the app delegate.