Question

I’m trying to create moving functionality to my imageView (maskPreview in the code below), so that users can move a picture, which is contained in maskPreview, around the screen. Here’s my code for touch begin and touch moved:

-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
if ([touches count]==1) {
    UITouch *touch= [touches anyObject];
    originalOrigin = [touch locationInView:maskPreview];
}
}
-(void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
if ([touches count]==1) {
    UITouch *touch = [touches anyObject];
    CGPoint lastTouch = [touch previousLocationInView:self.view];
    CGFloat movedDistanceX = originalOrigin.x-lastTouch.x;
    CGFloat movedDistanceY = originalOrigin.y-lastTouch.y;
    [maskPreview setFrame:CGRectMake(maskPreview.frame.origin.x+movedDistanceX, maskPreview.frame.origin.y + movedDistanceY, maskPreview.frame.size.width, maskPreview.frame.size.height)];
}
}

but I’m getting some weird responses from the app. I haven’t put restrictions on how far the imageview can move, i.e. to prevent it from going out of the screen, but even if it’s a small move, my imageview goes wild and disappears.

Thanks alot in advance for all the help

Answer 1

Implementing touchesBegan and so on is way overkill in this modern world. You’re just confusing the heck out of yourself, and your code will quickly become impossible to understand or maintain. Use a UIPanGestureRecognizer; that’s what it’s for. Making a view draggable with a UIPanGestureRecognizer is trivial. Here’s the action handler for a UIPanGestureRecognizer that makes the view draggable:

- (void) dragging: (UIPanGestureRecognizer*) p {
    UIView* vv = p.view;
    if (p.state == UIGestureRecognizerStateBegan ||
        p.state == UIGestureRecognizerStateChanged) {
        CGPoint delta = [p translationInView: vv.superview];
        CGPoint c = vv.center;
        c.x += delta.x; c.y += delta.y;
        vv.center = c;
        [p setTranslation: CGPointZero inView: vv.superview];
    }
}