UIImageView Gestures (Zoom, Rotate) Question

Hope this can be helpful to you, that’s how I usually implement gesture recognizers:

UIRotationGestureRecognizer *rotationGesture = [[UIRotationGestureRecognizer alloc] initWithTarget:self action:@selector(rotatePiece:)];
[piece addGestureRecognizer:rotationGesture];
[rotationGesture release];

UIPinchGestureRecognizer *pinchGesture = [[UIPinchGestureRecognizer alloc] initWithTarget:self action:@selector(scalePiece:)];
[pinchGesture setDelegate:self];
[piece addGestureRecognizer:pinchGesture];
[pinchGesture release];

Rotate method: Reset the gesture recognizer’s rotation to 0 after applying so the next callback is a delta from the current rotation

- (void)rotatePiece:(UIRotationGestureRecognizer *)gestureRecognizer {
    [self adjustAnchorPointForGestureRecognizer:gestureRecognizer];

    if ([gestureRecognizer state] == UIGestureRecognizerStateBegan || [gestureRecognizer state] == UIGestureRecognizerStateChanged) {
        [gestureRecognizer view].transform = CGAffineTransformRotate([[gestureRecognizer view] transform], [gestureRecognizer rotation]);
        [gestureRecognizer setRotation:0];
    }
}

Scale Method, at the end reset the gesture recognizer’s scale to 1 after applying so the next callback is a delta from the current scale

- (void)scalePiece:(UIPinchGestureRecognizer *)gestureRecognizer {
[self adjustAnchorPointForGestureRecognizer:gestureRecognizer];

    if ([gestureRecognizer state] == UIGestureRecognizerStateBegan || [gestureRecognizer state] == UIGestureRecognizerStateChanged) {
        [gestureRecognizer view].transform = CGAffineTransformScale([[gestureRecognizer view] transform], [gestureRecognizer scale], [gestureRecognizer scale]);
        [gestureRecognizer setScale:1];
    }
}

Than ensure that the pinch, pan and rotate gesture recognizers on a particular view can all recognize simultaneously prevent other gesture recognizers from recognizing simultaneously

- (BOOL)gestureRecognizer:(UIGestureRecognizer *)gestureRecognizer shouldRecognizeSimultaneouslyWithGestureRecognizer:(UIGestureRecognizer *)otherGestureRecognizer {
// if the gesture recognizers are on different views, don't allow simultaneous recognition
if (gestureRecognizer.view != otherGestureRecognizer.view)
    return NO;

// if either of the gesture recognizers is the long press, don't allow simultaneous recognition
if ([gestureRecognizer isKindOfClass:[UILongPressGestureRecognizer class]] || [otherGestureRecognizer isKindOfClass:[UILongPressGestureRecognizer class]])
    return NO;

    return YES;
}

Scale and rotation transforms are applied relative to the layer’s anchor point this method moves a gesture recognizer’s view’s anchor point between the user’s fingers

- (void)adjustAnchorPointForGestureRecognizer:(UIGestureRecognizer *)gestureRecognizer {
    if (gestureRecognizer.state == UIGestureRecognizerStateBegan) {
        UIView *piece = gestureRecognizer.view;
        CGPoint locationInView = [gestureRecognizer locationInView:piece];
        CGPoint locationInSuperview = [gestureRecognizer locationInView:piece.superview];

        piece.layer.anchorPoint = CGPointMake(locationInView.x / piece.bounds.size.width, locationInView.y / piece.bounds.size.height);
        piece.center = locationInSuperview;
    }
}