iOS - Accessing viewControllers on storyboard from appDelegate

Question

I've got an app using Core Data where I'm creating a managedObjectContext in the app delegate.

I want to pass that managedObjectContext to two view controllers on my storyboard so they are using the same managedObjectContext to save and fetch to and from.

I can access the first view controller with:

self.window.rootViewController

But the second view controller I want to access is then after a segue from the first and no reference is returned from it.

I tried:

instantiateViewControllerWithIdentifier:

But that creates a new instance of the view rather than allowing me to access the second view controller that appears after the segue.

So my question is, how can I access the second view controller?

Or (as I'm very new to this) is there a better way to be managing/passing the data between the view controllers?

Thanks in advance.

score 1 · Accepted Answer · edited May 23 '17 at 12:01

1

Or (as I'm very new to this) is there a better way to be managing/passing the data between the view controllers?

It depends on the data you're trying to pass around. In this case, you want to give your view controllers access to your Core Data managed object context. Because this is something you're going to need throughout the lifespan of your app it would be better to have your view controllers access it via your application delegate.

You can do this via [[UIApplication sharedApplication] delegate] - however, you may need to typecast it to avoid compiler warnings, or alternatively you might want to create a macro that returns the managed object context to save you time and make your code a little more readable.

If you told XCode you wanted to use Core Data when you created the project you should have the methods to retrieve your object context already in your app delegate. If not, you'll need to create them.

To create a macro to save you having to write out [[UIApplication sharedApplication] delegate] every time you need to access the managed object context, check out this answer: Short hand for [[UIApplication sharedApplication] delegate]?

edited May 23 '17 at 12:01

Community

1
1

answered May 28 '13 at 09:40

lxt

31,146
5
78
83

Thanks, @lxt I do have the standard methods in app delegate. So a better way to structure it would be to use `[[UIApplication sharedApplication] delegate]` within the views to access app delegate, and then call the xcode pre-written `- (NSManagedObjectContext *)managedObjectContext` method so they are all fetching from/saving to the same context? – Niazipan May 28 '13 at 09:51
Yep, that's right. But to save you time, you might want to create a macro. I'm going to update my answer to show you how to do that. – lxt May 28 '13 at 09:53
Thanks again, @lxt So following the format of the accepted answer in the link you added, I'd add the `#define AppDelegate (YourAppDelegate *)[[UIApplication sharedApplication] delegate]` to my AppDelegate.h and then in any view controller I could simply call `NSManagedObjectContext *managedObjectContext = [AppDelegate managedObjectContext]`? – Niazipan May 28 '13 at 10:04
Working. Thank you! Very elegant solution. – Niazipan May 28 '13 at 10:14

score 0 · Answer 2 · edited Aug 25 '16 at 00:13

You can go through this :-

  UINavigationController *navigationController = (UINavigationController *)self.window.rootViewController;
  MasterViewController *result;

//check to see if navbar "get" worked
   if (navigationController.viewControllers) {

//look for the nav controller in tab bar views 
      for (UINavigationController *view in navigationController.viewControllers) {

    //when found, do the same thing to find the MasterViewController under the nav controller
         if ([view isKindOfClass:[UINavigationController class]])
             for (UIViewController *view2 in view.viewControllers) 
                 if ([view2 isKindOfClass:[MasterViewController class]])                    
                     result = (MasterViewController *) view2;


      }
   }

iOS - Accessing viewControllers on storyboard from appDelegate

2 Answers2