为什么我不能用一个手指Swift旋转我的图像视图

Question

所以我正在制作一个DJ应用程序，我有一个转盘，我想用触摸向左和向右旋转。当播放歌曲时，我可以让它移动，但不知道如何使用触摸使它旋转。

编辑*******我已经开始工作了，但我需要用一个手指而不是两个手指来旋转图像视图。我该怎么做？谢谢

class ViewController: UIViewController, MPMediaPickerControllerDelegate {
    var angle: CGFloat = 0
    var rotate = UIRotationGestureRecognizer()
    override func viewDidLoad() {
        super.viewDidLoad()
        self.rotate = UIRotationGestureRecognizer(target: self, action: #selector(ViewController.rotate(_:)))
        self.leftTurnTable.addGestureRecognizer(self.rotate)
    }
    func rotate(r:UIRotationGestureRecognizer) {
        self.leftTurnTable.transform = CGAffineTransformMakeRotation(angle+r.rotation)
        if r.state == UIGestureRecognizerState.Ended {
            self.angle += r.rotation
        }
    }
} 

Answer 1

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

     let touch = touches.first
    if touch!.view === leftTurnTable {
        let position = touch!.locationInView(self.view)
        let target = leftTurnTable.center
        let angle = atan2(target.y-position.y, target.x-position.x)
        leftTurnTable.transform = CGAffineTransformMakeRotation(angle)
    }
}