Rotation gesture produces undesired rotation

Question

I need to rotate an UIImageview on user\'s motion using just one finger motion. For that I use a rotation gesture and then override touchesMoved with this code:

Answer 1

The problem is that you are saying

rotateImageView.transform = CGAffineTransformMakeRotation(angle)

So whatever transform the image view has already (from the previous rotation) is thrown away and completely replaced by a new transform starting at angle. That's the "jump" you are seeing.

What you want to do is apply a rotation transform to the existing transform of the image view. You can do that by calling CGAffineTransformRotate, instead of CGAffineTransformMakeRotation.

Answer 2

you may want to change self.superview to self.view (mine is subclass)

var xOffSet:CGVector = CGVectorMake(0, 0)
var yOffSet:CGVector = CGVectorMake(0, 0)
var origin:CGPoint = CGPointZero
var tempTransform=CGAffineTransform()
var startingAngle:CGFloat?


   override func touchesBegan(touches: Set<UITouch>, withEvent event: UIEvent?) {

    origin = (touches.first?.locationInView(self.superview))!
    xOffSet = CGVector(dx:(origin.x)-self.center.x, dy:(origin.y) - self.center.y)
    startingAngle = atan2(xOffSet.dy,xOffSet.dx)

    //save the current transform
    tempTransform = self.transform
}

override func touchesMoved(touches: Set<UITouch>, withEvent event: UIEvent?) {

    let touchPoint = touches.first?.locationInView(self.superview)
    yOffSet = CGVector(dx:touchPoint!.x - self.center.x, dy:touchPoint!.y - self.center.y)
    let angle = atan2(yOffSet.dy,yOffSet.dx)

    let deltaAngle = angle - startingAngle!
    self.transform = CGAffineTransformRotate(tempTransform, deltaAngle) 
}


override func touchesEnded(touches: Set<UITouch>, withEvent event: UIEvent?) {  
  startingAngle = nil
}

//reset in case drag is cancelled
override func touchesCancelled(touches: Set<UITouch>?, withEvent event: UIEvent?) {
        self.transform = tempTransform
        startingAngle = nil
    }