PanGesture以编程方式添加

Question

我不明白为什么UILabel动作不起作用。 如果我在StoryBoard中创建UILabel，则UIPanGesture不会有问题。

    func createLabel(textData: StoryText) {
        let label = UILabel(frame: textData.frame)
        let pan = UIPanGestureRecognizer(target: self, action: #selector(handlePan(recognizer:)))
        label.addGestureRecognizer(pan)
        label.isUserInteractionEnabled = true
        label.text = textData.text
        label.font = textData.font
        label.textColor = textData.color

        self.photoImageView.addSubview(label)
    }


    @objc func handlePan(recognizer:UIPanGestureRecognizer) {
      let translation = recognizer.translation(in: self.photoImageView)
      if let view = recognizer.view {
        view.center = CGPoint(x:view.center.x + translation.x,
                                y:view.center.y + translation.y)
      }
      recognizer.setTranslation(CGPoint.zero, in: self.photoImageView)
    }
}