（快速4）使用UIPanGestureRecognizer旋转视图但位置错误

Question

I have a container UIView and a button at right top of container, when I rotate button, I want to make container rotate by angle. But the code not work correctly just rotate fastly.

   @objc func btnRotatePanAction(sender: UIPanGestureRecognizer) {
    switch sender.state {
    case .began:
        origin = sender.location(in: self)
        break
    case .changed:
        let second = sender.location(in: self)
        let dx = second.x - origin.x
        let dy = second.y - origin.y
        let radians = atan2(dy, dx); // get bearing in radians
        print("rads: \(radians)")
        container.transform = container.transform.rotated(by: CGFloat(radians))
        origin = second
        break
    case .ended:
        break
    default: break

    }
}

Log output like this:

rads: 1.69022525281324

rads: 0.519146114246523

rads: 0.643501108793284

Answer 1

Do you transform the same view, which you applied UIPanGestureRecognizer to? It seems that you after transform coordinate system is also changed according to this transform and it changes every time btnRotatePanAction(_:) called. That's why everythings turn around rapidly (and randomly I guess).

You can add a subview to view which handles UIPanGestureRecognizer and transform subview not main view.

And by the way, instead of saving origin position of tap you can just use sender.translation(in: sender.view!) which returns how touch is changed in coordinate system.