UIScreenEdgePanGestureRecognizer Triggering Multiple Times

Question

I have the following code in a viewDidLoad on a UIViewController:

UIScreenEdgePanGestureRecognizer *edgeRecognizer = [[UIScreenEdgePanGestureRecognizer alloc] initWithTarget:self action:@selector(handleRightEdgeSwipe:)];
edgeRecognizer.edges = UIRectEdgeRight;
[self.view addGestureRecognizer:edgeRecognizer];

and the purposes is to trigger a view to slide in when a right edge gesture is detected.

-(void)handleRightEdgeSwipe:(UIGestureRecognizer*)sender
{
NSLog(@"Showing Side Bar");
[self presentPanelViewController:_lightPanelViewController withDirection:MCPanelAnimationDirectionRight];
}

But I am seeing that the "handleRightEdgeSwipe" function is triggered multiple times - sometimes 5 times which makes the side bar view that should smoothly animate slide in to flash multiple times.

(NOTE: I tried triggering the view to appear from a UIButton and it works fine).

Why is the right edge gesture triggered multiple times and how can I fix it?

Answer 1

As noted, the UIScreenEdgePanGestureRecognizer invokes your action multiple times as the state of the GestureRecognizer changes. See the documentation for the state property of the UIGestureRecognizer class. So, in your case I believe the answer you're looking for is to check if the state is "ended". Thus:

-(void)handleRightEdgeSwipe:(UIGestureRecognizer*)sender
{
    if (sender.state == UIGestureRecognizerStateEnded)
    {
        NSLog(@"Showing Side Bar");
        [self presentPanelViewController:_lightPanelViewController withDirection:MCPanelAnimationDirectionRight];
   }
}

Answer 2

This gesture is not a single-shot event but continuous.

handleRightEdgeSwipe: is called once whenever sender.state changes or the touch moved around. You have to move the UIButton depending on the gesture's state and locationInView:.