Question

I want to rotate the image in clockwise or anticlockwise direction corresponding to the user touch drag with its speed. I think this can be done with some math and logic. What would a code sample for this look like?

Answer 1

If you’re targeting iOS 3.2 or greater, you can use UIRotationGestureRecognizer. The code would look something like this:

In your setup method (viewDidLoad or init, etc,):

UIRotationGestureRecognizer *rotationGesture = 
  [[UIRotationGestureRecognizer alloc] initWithTarget:self
                                               action:@selector(handleRotate:)];
rotationGesture.delegate = self;
[myImageView addGestureRecognizer:rotationGesture];
[rotationGesture release];

The event handler:

- (void)handleRotate:(UIRotationGestureRecognizer *)recognizer {
  if(recognizer.state == UIGestureRecognizerStateBegan || 
     recognizer.state == UIGestureRecognizerStateChanged)
  {
    recognizer.view.transform = CGAffineTransformRotate(recognizer.view.transform, 
                                                        recognizer.rotation);
    [recognizer setRotation:0];
  }
}

I have some more examples of gesture recognizers (including the one above) on github.