Question

Having a little trouble with my app. I am questioning my approach.

Here is an image

Basically i need the color wheel to spin in the transparent box. What I have so far is working. I can drag the color wheel and it will rotate. The problem is I can touch and drag ‘anywhere’ on the screen and it will rotate. I only want it to rotate in the ‘window’.

I basically added a UIView and an UIImageView, added outlets to the ImageView and added code in touchesBegan and touchesMoved to perform the animation. The wheel is a full circle image and subviews are ‘clipped’ to no show the lower half of the image.

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
    UITouch *thisTouch = [touches anyObject];
    delta = [thisTouch locationInView:wheelImage];

    float dx = delta.x  - wheelImage.center.x;
    float dy = delta.y  - wheelImage.center.y;
    deltaAngle = atan2(dy,dx); 

    initialTransform = wheelImage.transform;   
  }

  - (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {
      UITouch *touch = [touches anyObject];
  CGPoint pt = [touch locationInView:wheelImage];

  float dx = pt.x  - wheelImage.center.x;
  float dy = pt.y  - wheelImage.center.y;
  float ang = atan2(dy,dx);

  //do the rotation
  if (deltaAngle == 0.0) {
    deltaAngle = ang;
    initialTransform = wheelImage.transform;
  }else
  {
    float angleDif = deltaAngle - ang;
    CGAffineTransform newTrans = CGAffineTransformRotate(initialTransform, -angleDif);
    wheelImage.transform = newTrans;
    
    currentValue = [self goodDegrees:radiansToDegrees(angleDif)];
    
  }

  }

Now…My questions are the following:

1. How can I get the touchesMoved/Began ONLY to work on the UIView or UIImageView?
2. Should I create a Custom UIView for this wheel and then just add it to my main view controller?
   2.a. If I do create a custom, will I have the same issue with the touches?

Answer 1

You may want to consider using a UISwipeGestureRecognizer and adding it to only the view in which you wish to recognize the swipe.