如何检测UISwipeGestureRecognizer的结束？

Question

From the Apple documentation

A swipe is a discrete gesture, and thus the associated action message is sent only once per gesture.

-(void)touchesEnded:(NSSet *)touches withEvent:(UIEvent*)event 

also doesn't gets called when I use UISwipeGestureRecognizer

How can I detect when the user lifts his finger?

Answer 1

I figured it out, actually it was quite easy, instead of using UISwipeGestureRecognizer to detect swipes I detected it myself using event handling

-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event{
    UITouch *touch = [touches anyObject];
    self.initialPosition = [touch locationInView:self.view];

 }
-(void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event{
     UITouch *touch = [touches anyObject];
     CGPoint movingPoint = [touch locationInView:self.view];
     CGFloat moveAmt = movingPoint.y - self.initialPosition.y;
     if (moveAmt < -(minimum_detect_distance)) {
       [self handleSwipeUp];
     } else if (moveAmt > minimum_detect_distance) {
       [self handleSwipeDown];
     }
  }
 -(void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event{
      [self reset];

  }
 -(void)touchesCancelled:(NSSet *)touches withEvent:(UIEvent *)event{
     [self reset];
  }

I haven't subclassed UIGestureRecognizer but did the event handling in the required view controller only, as in reset method I am resetting few variable, counters and timers belonging to the view controller.

Answer 2

I think better you need to examine the state property of the gesture recognizer:

- (void)swipe:(UISwipeGestureRecognizer *)recognizer
{
   CGPoint point = [recognizer locationInView:[recognizer view]];
   if (recognizer.state == UIGestureRecognizerStateBegan)
       NSLog(@"Swipe began");
   else if (recognizer.state == UIGestureRecognizerStateEnded)
       NSLog(@"Swipe ended");
}

Answer 3

UISwipeGestureRecognizer is a discrete gesture as the Apple documentation said, so you need to use a continuous gesture, in this case use UIPanGestureRecognizer.

Here is the code:

- (void)viewDidLoad{
[super viewDidLoad];

// add pan recognizer to the view when initialized
UIPanGestureRecognizer *panRecognizer = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(panRecognized:)];
[panRecognizer setDelegate:self];
[yourView addGestureRecognizer:panRecognizer]; // add to the view you want to detect swipe on
}


-(void)panRecognized:(UIPanGestureRecognizer *)sender{

CGPoint distance = [sender translationInView: yourView];


if (sender.state == UIGestureRecognizerStateEnded) {
    [sender cancelsTouchesInView];


    if (distance.x > 70 && distance.y > -50 && distance.y < 50) { // right

        NSLog(@"user swiped right");
        NSLog(@"distance.x - %f", distance.x);

    } else if (distance.x < -70 && distance.y > -50 && distance.y < 50) { //left

        NSLog(@"user swiped left");
        NSLog(@"distance.x - %f", distance.x);

    }

    if (distance.y > 0) { // down
        NSLog(@"user swiped down");
        NSLog(@"distance.y - %f", distance.y);
    } else if (distance.y < 0) { //up
        NSLog(@"user swiped up");
        NSLog(@"distance.y - %f", distance.y);
    }

}
}

Don't forget to add UIGestureRecognizerDelegate.

Answer 4

If you use scrollView, you can detect contentOffset of it

func scrollViewDidScroll(_ scrollView: UIScrollView) {
    if scrollView.contentOffset.y < -100 { // how you needed
        // do what you need
    }
}