Custom iOS 7 UIViewController transition save loop

Question

I create custom transitions in my application and run into two problems. If I installed a view controller to handle both UIViewControllerAnimatedTransitioning and UIViewControllerTransitioningDelegate , I ran into a problem with my view controller, which is never freed. In particular, this creates a persistence:

 self.transitioningDelegate = self; 

If I do not, put the UIViewControllerAnimatedTransitioning and UIViewControllerTransitioningDelegate in a separate NSObject called TransitionController and set it like this:

 self.transitioningDelegate = [[TransitionController alloc] init]; 

UIViewController freed , but I get memory leaks in the TransitionController object. Anyone now what am I doing wrong?

Answer 1

I ran into the same problem and was able to solve it.
The custom transition API is not well documented and requires a lot of trial and error so that I can fix it.

Let me tell you how I was able to get it working without memory problems:

Here are the players:

VCA = view controller that wants to introduce VCB modally
VCB = Modified View Controller (represented by VCA)

TC = Custom transition controller object that performs custom animation.
A subclass of NSObject that matches "UIViewControllerAnimatedTransitioning".
An instance will be created inside TD.

TD = Custom transition delegate object that the transition controller provides to the system. A subclass of NSObject that matches "UIViewControllerTransitioningDelegate"

Now imagine a VCB instance

self = VCA instance
myModalViewController = is a strong self property

 self.myModalViewController = [[VCB alloc] init]; [self.myModalViewController setModalPresentationStyle: UIModalPresentationCustom]; [self.myModalViewController setTransitioningDelegate: [[TD alloc] init]]; [self presentViewController: self.myModalViewController animated:YES completion:NULL]; 

At some point later, the VCB asks to reject the VCA

self = VCA instance
myModalViewController = VCB Instance Presented Above

 [self dismissViewControllerAnimated:YES completion:^{ [self.myModalViewController setTransitioningDelegate: nil]; // DO THIS!!!! self.myModalViewController = nil; }]; 

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Hope this helps. This is definitely for me.

Answer 2

In my case, I myself ( UIViewController ) held an instance of a custom UIViewController (lets call it mViewController ), and self is a transitioningDelegate to show / reject mViewConroller . My solution to avoiding the save loop was to call it inside .m mViewController :

 -(void)viewDidDisappear:(BOOL)animated { self.transitioningDelegate = nil; [super viewDidDisappear:animated]; } 

Worked like a charm (:

Answer 3

In the second attempt, you allocate an instance of the TransitionController and it will never be released (since no one is referencing it). Objects should not store delegates in Objective-C, so you need to have a link to your ViewController and delegate to it from another point in your code.

Answer 4

The UIViewControllerAnimatedTransitioning object UIViewControllerAnimatedTransitioning saved using the "from" VC after the transition is completed in iOS7 (this does not happen in iOS8), which may cause a memory leak if your transition object stores anything in the properties. This is a bit of me in the past, you need to be careful.

Answer 5

In my case, what caused the persistence of my submitted view controller was that I passed the wrong logic code to the completion block of my animation.

 [transitionContext completeTransition:transitionContext.transitionWasCancelled]; 

It should be like this:

 BOOL successful = transitionContext.transitionWasCancelled == NO; [transitionContext completeTransition:successful]; 

Splitting the code into two lines helps readability.