Same Viewcontroller pops multiple times

Question

Required:

I want to enable iOS7 swipe to back feature with custom navigation back button item.

Current Implementation:

After researching a lot, I found the following solution to be best:

1. Set the delegate of the gesture recognizer as follows

   self.navigationController.interactivePopGestureRecognizer.delegate = (id<UIGestureRecognizerDelegate>)self;
   

2. This, creates a lot of bugs as mentioned in this stackoverflow answer. To avoid that, subclassing the UINavigationController seems to be the only feasible option. I did that as mentioned in this blog by Keighl.

Problem:

Basic swipe to back feature is working, but the strange thing is that, sometimes, the same viewController that is being dismissed, appears again after the pop action is completed.

i.e. suppose the navigation stack looks like A -> B. Popping B will again bring up B. This keeps on happening until eventually the viewController B actually gets dismissed and A appears.

This happens to all views in all viewController objects and not just to a specific one. Also, I have ensured that the push method is called only once at all places.

I also tried logging the navigation stack at each point, but there is only one instance of each viewController.

Point to note:

I need to disable the swipe feature in certain views. I did this by writing the code to disable and enable the swipe gesture in viewDidAppear and viewDidDisappear respectively.

Please provide your valuable suggestions or a solution to this problem. Thanks!

Answer 1

Short answer: You should add a UIScreenEdgePanGestureRecognizer to your view controller if you want to add a pop gesture where none exists. Modifying the existing interactivePopGestureRecognizer is probably not the right approach. Do this:

[self addGestureRecognizer:({
    UIScreenEdgePanGestureRecognizer *gesture =
        [[UIScreenEdgePanGestureRecognizer alloc]
        initWithTarget:self action:@selector(pop)];
    gesture;
})];

and

-(void)pop {
    // pop your view controller here
}

Long answer: Forcing the interactivePopGestureRecognizer.delegate is what breaks your code.

If you need to cast self as such:

self.navigationController.interactivePopGestureRecognizer.delegate =
    (id<UIGestureRecognizerDelegate>)self;

...it is because self is not a UIGestureRecognizerDelegate. The following should compile, link, build and run or you are setting yourself up for trouble:

self.navigationController.interactivePopGestureRecognizer.delegate = self;

Note that being a UIGestureRecognizerDelegate specifically allows you to tweak a gesture's behavior at runtime, assuming you are implementing one of the following and ensuring that the tweak applies to a gesture you own:

1. gestureRecognizerShouldBegin:
2. gestureRecognizer:shouldReceiveTouch:
3. gestureRecognizer:shouldRecognizeSimultaneouslyWithGestureRecognizer:
4. gestureRecognizer:shouldRequireFailureOfGestureRecognizer:
5. gestureRecognizer:shouldBeRequiredToFailByGestureRecognizer:

By constantly changing the delegate of that interactivePopGestureRecognizer you did not create, all you are doing is preventing the iOS behavior to take place.

From the documentation

UINavigationController -interactivePopGestureRecognizer

The gesture recognizer responsible for popping the top view controller off the navigation stack. (read-only)

In plain English: Use this value is you need to combine that gesture with your own gesture. But you are not supposed to modify its behavior:

...You can use this property to retrieve the gesture recognizer and tie it to the behavior of other gesture recognizers in your user interface...