UIImageView 的向上和向下触摸动作

Question

我想要实现的是当用户触摸 UIImageView 时设置 Image1，当用户抬起手指时设置 Image2。

我只能得到 UIGestureRecognizerState.Ended 这个代码

 var tap = UITapGestureRecognizer(target: self, action: Selector("tappedMe:"))     

        imageView.addGestureRecognizer(tap)
        imageView.userInteractionEnabled = true

func tappedMe(gesture: UITapGestureRecognizer)
{

    if gesture.state == UIGestureRecognizerState.Began{
        imageView.image=originalImage
        dbgView.text="Began"
    }else if  gesture.state == UIGestureRecognizerState.Ended{
        imageView.image=filteredImage
        dbgView.text="Ended"
    }else if  gesture.state == UIGestureRecognizerState.Cancelled{
        imageView.image=filteredImage
        dbgView.text="Cancelled"
    }else if  gesture.state == UIGestureRecognizerState.Changed{
        imageView.image=filteredImage
        dbgView.text="Changed"
    }

}

Answer 1

UITapGestureRecognizer 不会将其状态更改为.Began，但 UILongPressGestureRecognizer 会。如果您出于某种原因想要直接覆盖触摸回调，您可以使用带有非常短 minimumPressDuration 的 UILongPressGestureRecognizer 来实现效果。

@Daij-Djan 的示例：

class ViewController: UIViewController {
  override func viewDidLoad() {
    super.viewDidLoad()

    // Do any additional setup after loading the view, typically from a nib.

    var tap = UILongPressGestureRecognizer(target: self, action: Selector("pressedMe:"))
    tap.minimumPressDuration = 0
    self.view.addGestureRecognizer(tap)
    self.view.userInteractionEnabled = true
  }

  func pressedMe(gesture: UITapGestureRecognizer) {
    if gesture.state == .Began{
      self.view.backgroundColor = UIColor.blackColor()
    } else if  gesture.state == .Ended {
      self.view.backgroundColor = UIColor.whiteColor()
    }
  }
}

Answer 2

解决办法如下：

override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
    if let touch = touches.first {
        if touch.view == self {
            //began
        }
    }
    super.touchesBegan(touches, with: event)
}

override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent?) {
    if let touch = touches.first {
        if touch.view == self {
            //end
        }
    }
    super.touchesEnded(touches, with: event)
}

注意：把这个放在 UIView 的子类中，并在 init 块中添加：userInteractionEnabled = true

Answer 3

最好和最实用的解决方案是将您的 UIImageView 嵌入到 UIControl 子类中。

默认情况下UIImageView 已启用用户交互。如果您创建一个简单的UIControl 子类，您可以轻松地将您的图像视图添加到其中，然后使用以下方法来实现您想要的：

let control = CustomImageControl()
control.addTarget(self, action: "imageTouchedDown:", forControlEvents: .TouchDown)
control.addTarget(self, action: "imageTouchedUp:", forControlEvents: [ .TouchUpInside, .TouchUpOutside ])

这样做的好处是您可以访问所有不同的触摸事件，从而节省您自己检测它们的时间。

根据您想要执行的操作，您还可以覆盖 var highlighted: Bool 或 var selected: Bool 以检测用户何时与图像交互。
最好采用这种方式，以便您的用户在其应用中的所有控件上获得一致的用户体验。

一个简单的实现如下所示：

final class CustomImageControl: UIControl {

    let imageView: UIImageView = UIImageView()

    override init(frame: CGRect) {
        super.init(frame: frame)

        // setup our image view
        imageView.translatesAutoresizingMaskIntoConstraints = false
        addSubview(imageView)
        imageView.leadingAnchor.constraintEqualToAnchor(leadingAnchor).active = true
        imageView.trailingAnchor.constraintEqualToAnchor(trailingAnchor).active = true
        imageView.topAnchor.constraintEqualToAnchor(topAnchor).active = true
        imageView.bottomAnchor.constraintEqualToAnchor(bottomAnchor).active = true
    }

    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
}

final class MyViewController: UIViewController {


    override func viewDidLoad() {
        super.viewDidLoad()

        let control = CustomImageControl()
        control.translatesAutoresizingMaskIntoConstraints = false
        control.imageView.image = ... // set your image here.
        control.addTarget(self, action: "imageTouchedDown:", forControlEvents: .TouchDown)
        control.addTarget(self, action: "imageTouchedUp:", forControlEvents: [ .TouchUpInside, .TouchUpOutside ])

        view.addSubview(control)
        control.centerXAnchor.constraintEqualToAnchor(view.centerXAnchor).active = true
        control.centerYAnchor.constraintEqualToAnchor(view.centerYAnchor).active = true
    }

    @objc func imageTouchedDown(control: CustomImageControl) {
        // pressed down on the image
    }

    @objc func imageTouchedUp(control: CustomImageControl) {
        // released their finger off the image
    }
}