How to use useLayoutToLayoutNavigationTransitions in UICollectionView?

Question

I was trying to learn the new layout transition effect in iOS7 collection view.

However, I am unable to get it to work at all. I have attached a screen shot description below.

I am aware that the same Collection View is used between Controllers when this Transition effect is in effect. But, why that collection view is not reloading when transition is happening. I even tried Reloading the collection view an that too failed.

There should be some simple point I should be missing. Help me please.

I have attached the source code below.

    UICollectionViewFlowLayout *flowLayout = [[UICollectionViewFlowLayout alloc] init];
    flowLayout.itemSize = CGSizeMake(75.0, 70.0);

    ALCollectionViewNoXibController* controller = [[ALCollectionViewNoXibController alloc] initWithCollectionViewLayout:flowLayout];
    controller.numberOfItems = _numberOfItems-1;
controller.transitionType = _transitionType;
    if (_transitionType == kLayoutTransition) {
        controller.useLayoutToLayoutNavigationTransitions = YES;
    }
   [self.navigationController pushViewController:controller animated:YES];

Project Code

Answer 1

The new flowLayout that you are loading is indeed being used. You can see it if for instance, you do flowLayout.itemSize = CGSizeMake(10.0*_numberOfItems, 10.0*_numberOfItems);

Your issue is that in order to make the transition work, iOS will change your datasource during the animated transition.

Try this:

Make your class a Navigation delegate:

@interface ALCollectionViewNoXibController ()<UINavigationControllerDelegate>

Then set the delegate of the navigation to the current controller, before pushing

self.navigationController.delegate = self;
[self.navigationController pushViewController:controller animated:YES];

Now you can add

- (void)navigationController:(UINavigationController *)navigationController didShowViewController:(UIViewController *)viewController animated:(BOOL)animated {

   ALCollectionViewNoXibController *controller = (ALCollectionViewNoXibController *)viewController;
   navigationController.delegate = controller;
   controller.collectionView.dataSource = controller;
}

This simple example will break when you navigate back to the top controller, because the viewController received is not of ALCollectionViewNoXibController class. But you get the idea.