Question

I have this code that retrieves the coordinates of an object when it is panned:

UITapGestureRecognizer *moveBuildingTap = [[UITapGestureRecognizer alloc]
                                           initWithTarget:self action:@selector(moveobject:)];

Method moveobject contents:

CGPoint tapPoint=[recognizer locationOfTouch:0 inView:self.view];

I use this to change the frame of – move it -an imageview using these coordinates.

However, upon dragging the image around – triggering the uipangesturerecognizer action, I found that when I drag it to the absolute bottom, I get an error that -[UIPanGestureRecognizer locationOfTouch:inView:]: index (0) beyond bounds (0).

How can I solve this exception and prevent the user from dragging past this point?

Thanks

Answer 1

It’s weird that your moveobject: method gets called even though the private touches array of the gesture recognizer seems to be empty.

Anyway, in general, if you don’t handle multitouch gestures within gesture recognizer, I would suggest to use [recognizer locationInView:] rather then locationOfTouch:inView:.

Btw:

Your talking about a UIPanGestureRecognizer while in the code you’re using a UITapGestureRecognizer.

The code I would recommend to handle dragging of a particular view looks like this:

//...
UIPanGestureRecognizer *panGR = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(handlePan:)];
[someView addGestureRecognizer:panGR];
//...

- (void)handlePan:(UIPanGestureRecognizer *)gr
{
    CGPoint translation = [gr translationInView:gr.view];
    gr.view.frame = CGRectOffset(gr.view.frame, translation.x, translation.y);
    [gr setTranslation:CGPointZero inView:gr.view];
}