UIPanGestureRecognizer-拖动后视图消失

Question

I have a strange problem with using UIPanGestureRecognizer to move a view from the top of the screen. Everything works perfect in simulator but on the actual device the view dissappears when I touch it.

- (IBAction)handlePan:(UIPanGestureRecognizer *)recognizer {

    CGPoint start;

    if (recognizer.state == UIGestureRecognizerStateBegan) {
        start = [recognizer translationInView:self.view];
        originCenter = recognizer.view.center.y;
    }

    if (recognizer.state == UIGestureRecognizerStateChanged) {
        CGPoint translation = [recognizer translationInView:self.view];
        if (down) {
            if (originCenter + translation.y < self.view.center.y && self.view.center.y + translation.y < self.view.center.y) {
                CGPoint move = CGPointMake(self.view.frame.size.width/2, originCenter-(start.y-translation.y));
                [recognizer.view setCenter:move];
            }
        }else{
            if (originCenter + translation.y < self.view.center.y && originCenter + translation.y > originCenter) {
                CGPoint move = CGPointMake(self.view.frame.size.width/2, originCenter-(start.y-translation.y));
                [recognizer.view setCenter:move];
            }
        }
    }

    if([recognizer state] == UIGestureRecognizerStateEnded  || [recognizer state] == UIGestureRecognizerStateCancelled ){
        if(recognizer.view.center.y > -40){

            [recognizer.view setFrame:CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height)];

            down = TRUE;
        }else{

            [recognizer.view setFrame:CGRectMake(0, 80-self.view.frame.size.height, self.view.frame.size.width, self.view.frame.size.height)];

            down = FALSE;
        }
    }
}

There is one thing that comes to my mind that there might be problem with calculating the position on the device and the view is moved outside the screen. Is that possible?

Answer 1

If nothing else, you should make start a static or an ivar. Otherwise, when you hit UIGestureRecognizerStateChanged , start will not have preserved the value it had during UIGestureRecognizerStateBegan .