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;
    }
}

Just implement gestureRecognizer:shouldRecognizeSimultaneouslyWithGestureRecognizer: in your delegate.

I have a UIPinchGestureRecognizer, a UIPanGestureRecognizer and a UIRotationGestureRecognizer set up and I want them all to work at the same time. I also have a UITapGestureRecognizer which I do not want to be recognized simultaneously. All I did was this:

- (BOOL)gestureRecognizer:(UIGestureRecognizer *)gestureRecognizer shouldRecognizeSimultaneouslyWithGestureRecognizer:(UIGestureRecognizer *)otherGestureRecognizer
{
    if (![gestureRecognizer isKindOfClass:[UITapGestureRecognizer class]] && ![otherGestureRecognizer isKindOfClass:[UITapGestureRecognizer class]]) {
        return YES;
    }

    return NO;
}

I found something that may interest you on the stanford university website:

http://www.stanford.edu/class/cs193p/cgi-bin/drupal/downloads-2010-winter

on this site you will need to scroll down until you see the number 14: "Title: Lecture #14 - MultiTouch"

Download the: "14_MultiTouchDemo.zip"

In this example you can scale and rotate every image at the same time.

hope i helped :)

When you use CGAffineTransformMakeScale, you are resetting the transformation of Identity every time you use it and you lose the previous transformation information.

Try using CGAffineTransformScale(view.transform,scale, scale) for the pinch zooming. You will need to retain the original frame size to keep the zooming under control though.
see: How can I use pinch zoom(UIPinchGestureRecognizer) to change width of a UITextView?

For rotation similarly:

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