在UIImageView上测试捏（不是捏和缩放-只是测试捏）

Question

This isn't another one of "those" questions, don't worry.

Basically I want to test for a pinch and then run an animation. Here is the code I currently have:

// test for a pinch
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
    NSSet *allTouches = [event allTouches];
    if([allTouches count] == 2){
        //there are two touches...
        UITouch *firstTouch = [[allTouches allObjects] objectAtIndex:0];
        UITouch *secondTouch = [[allTouches allObjects] objectAtIndex:1];
        CGPoint firstPoint = [firstTouch locationInView:self.superview];
        CGPoint secondPoint = [secondTouch locationInView:self.superview];

        int X1 = firstPoint.x;
        int Y1 = firstPoint.y;
        int X2 = secondPoint.x;
        int Y2 = secondPoint.y;

        // lets work out the distance:
        // sqrt( (x2-x1)^2 + (y2-y1)^2 );
        preDistance = sqrtf( (float)pow((X2-X1),2) + (float)pow((Y2-Y1),2) );

    }
}

- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event {
    NSSet *allTouches = [event allTouches];
    if([allTouches count] == 2){
        //there are two touches...
        UITouch *firstTouch = [[allTouches allObjects] objectAtIndex:0];
        UITouch *secondTouch = [[allTouches allObjects] objectAtIndex:1];
        CGPoint firstPoint = [firstTouch locationInView:self.superview];
        CGPoint secondPoint = [secondTouch locationInView:self.superview];

        int X1 = firstPoint.x;
        int Y1 = firstPoint.y;
        int X2 = secondPoint.x;
        int Y2 = secondPoint.y;

        // lets work out the distance:
        // sqrt( (x2-x1)^2 + (y2-y1)^2 );
        postDistance = sqrtf( (float)pow((X2-X1),2) + (float)pow((Y2-Y1),2) );

        // lets test now
        // if the post distance is LESS than the pre distance then
        // there has been a pinch INWARDS
        if(preDistance > postDistance){
            NSLog(@"Pinch INWARDS");
            // so we need to move it back to its small frame
            if(CGRectEqualToRect(self.frame, largeFrame) && !CGRectIsEmpty(self.smallFrame)){
                // we can go inwards
                [UIView beginAnimations:nil context:nil];
                [UIView setAnimationDuration:0.5];
                self.frame = smallFrame;
                [UIView commitAnimations];
            }
        }
        else {
            NSLog(@"Pinch OUTWARDS");
            // so we need to move it back to its small frame
            if(!CGRectEqualToRect(self.frame, largeFrame)){
                // we can go outwards
                // set org frame
                smallFrame = self.frame; // so we can go back later
                [UIView beginAnimations:nil context:nil];
                [UIView setAnimationDuration:0.5];
                self.frame = largeFrame;
                [UIView commitAnimations];
            }
        }

    }
}

All it does is measure the distance between the two touches if there is a multi touch, then it measures the distance again when the touches end. If the difference between the two is positive then it was an outwards pinch, and if it was negative it was an inwards pinch.

Depending on the direction of the pinch the image view will scale bigger or smaller to and from set CGRects (this is why I don't want the "normal" pinch and zoom functionality). I just want it to be a gesture to scale an image up and down again.

However, this isn't working very well... it doesn't always pick up pinches. I don't know if this is because the view its in is also detecting touches (only single pinches), but still...

Anyway, I was wondering if anyone has a better way of detecting pinches? I've currently subclassed the UIImageView to create my ImageController class which has these touch methods in them. All I need to know is a) they are touching this image and b) which direction they've pinched in.

Thanks

Answer 1

Check out UIPinchGestureRecognizer in the documentation. I haven't used it, but seems like it's just what you need.

Answer 2

Anyway, I was wondering if anyone has a better way of detecting pinches?

If you're targeting iOS 3.2 and upwards you can use gesture recognizers - there's no good reason not to. If you need to target pre 3.2, then your above approach (or varients therein, using touchesBegin, etc) is the only way, so it's just tweaking the algorithm.

If you can , I'd strongly recommend using UIPinchGestureRecognizer . It will make your life considerably easier, as it handles all the details. If you want to detect both the scale and direction of the pinch you can combine UIPinchGestureRecognizer with a UIRotationGestureRecognizer - the former will just give you the scale of a pinch, not the relative angle.

Answer 3

If you can live without 3.1.x devices I would recommend that you use the UIPinchGestureRecognizer . It's very simple to use, but the problem is that you're only going to be able to run it on iOS devices running 3.2 and upwards.

For some reason you are using locationInView to identify the position of the touches. Have you tried identifying the touches location in the current view (the actual image view)? Calling superview means that you will get the position of the touches in the view that contains your image view.