ios - 为什么在 Xamarin IOS customrenderer 中没有准确检测到长按开始/结束？

Question

我有一个 Xamarin Forms 项目，我想在其中有一个按钮，必须按长 才能触发事件。除了长按事件，我还需要按下按钮的确切时间，因为那时我想在 UI 上启动一些动画。

我制作了一个自定义渲染器来解决它，在 Android 上它可以工作，但在 IOS 上我有问题:有时它可以工作，有时不能。

在 IOS 上我是这样做的:我使用 TouchDown 事件来获取触摸的确切时间，TouchUpInside 结束，UILongPressGestureRecognizer 长按。有时它就像一个魅力，但有时只有 UILongPressGestureRecognizer 的事件被触发而没有触发 TouchDown。

这是我的代码:

[assembly: ExportRenderer(typeof(LongPressButton), typeof(LongPressButtonRenderer))]

 namespace AnyProj.iOS
{
public class LongPressButtonRenderer : ButtonRenderer
{
    private LongPressButton _longPressButton;

    private UILongPressGestureRecognizer _longPressGestureRecognizer;

    public LongPressButtonRenderer()
    {

    }

    protected override void OnElementChanged(ElementChangedEventArgs<Button> e)
    {
        base.OnElementChanged(e);

        _longPressGestureRecognizer = new UILongPressGestureRecognizer(() => HandleLongPress());

        if(e.NewElement == null)
        {
            if (_longPressGestureRecognizer != null)
            {
                this.RemoveGestureRecognizer(_longPressGestureRecognizer);
            }
        }

        if(e.OldElement == null)
        {
            _longPressButton = (LongPressButton)e.NewElement;
            Control.TouchDown += (sender, ee) => {
                Debug.WriteLine("Sometimes triggered, sometimes not.");
            };
            Control.TouchUpInside += (sender, ee) => {
                Debug.WriteLine("Sometimes triggered, sometimes not.");
            };
            _longPressGestureRecognizer.MinimumPressDuration = 2.0;
            this.AddGestureRecognizer(_longPressGestureRecognizer);
        }
    }

    private void HandleLongPress()
    {
        try
        {
            if (_longPressGestureRecognizer.State == UIGestureRecognizerState.Began)
                Debug.WriteLine("Sometimes triggered, sometimes not.");
        }
        catch(Exception exc)
        {
            Debug.Assert(false,exc.Message);
        }
    }
}
}

你能帮我改进一下吗？非常感谢!

更新:它发生在真实设备 (iPhone SE) 上，在模拟器上它总是像一个魅力!

更新 2:我在 Swift 中做了一个小测试项目来实现这个功能，效果很好，所以没有像通过 Xamarin 表单那样出现类似的错误。

class ViewController: UIViewController {

@IBOutlet weak var longPressButton: UIButton!
override func viewDidLoad() {
    super.viewDidLoad()

    longPressButton.addTarget(self, action:#selector(touchDown), for: .touchDown)
    longPressButton.addTarget(self, action:#selector(touchUp), for: .touchUpInside)

    let longGesture = UILongPressGestureRecognizer(target: self, action: #selector(longTap(_:)))
    longGesture.minimumPressDuration = 2.0
    longPressButton.addGestureRecognizer(longGesture)
}

override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
    // Dispose of any resources that can be recreated.
}

@objc func touchUp(){
    print("Touch up")
}

@objc func touchDown(){
    print("Touch down")
}

@objc func longTap(_ sender: UIGestureRecognizer){
    print("Long tap")
    if sender.state == .ended {
        print("UIGestureRecognizerStateEnded")
    }
    else if sender.state == .began {
        print("UIGestureRecognizerStateBegan.")
    }
}

Answer 1

我已经在我的项目中测试了以下代码，它运行良好。在 iPhone 5c 物理设备上测试。请注意，如果长按开始，将不会调用 HandleTouchUpInside；相反，您可以从 UILongPressGestureRecognizer 的 UIGestureRecognizerState.Ended 状态确定结束。

protected override void OnElementChanged(ElementChangedEventArgs<Button> e)
{
    base.OnElementChanged(e);

    if (e.OldElement != null)
    {
        RemovePressEvents();
    }

    if (e.NewElement != null)
    {
        AddPressEvents();
    }
}

private void AddPressEvents()
{
    _longPressGestureRecognizer = new UILongPressGestureRecognizer(HandleLongPress);
    Control.TouchDown += HandleTouchDown;
    Control.TouchUpInside += HandleTouchUpInside;
    AddGestureRecognizer(_longPressGestureRecognizer);
}

private void RemovePressEvents()
{
    Control.TouchDown -= HandleTouchDown;
    Control.TouchUpInside -= HandleTouchUpInside;
    RemoveGestureRecognizer(_longPressGestureRecognizer);
}

private void HandleTouchDown(object sender, EventArgs e)
{
    System.Diagnostics.Debug.WriteLine("TOUCH DOWN");
}

private void HandleTouchUpInside(object sender, EventArgs e)
{
    // Note: will not be called if the Long Press begins. Instead,
    // You can determine the end of the press from when HandleLongPress
    // is called and UILongPressGestureRecognizer.State = 
    // UIGestureRecognizerState.Ended
    System.Diagnostics.Debug.WriteLine("TOUCH UP INSIDE");
}

private void HandleLongPress(UILongPressGestureRecognizer o)
{
    switch (o.State)
    {
        case UIGestureRecognizerState.Began:
            System.Diagnostics.Debug.WriteLine("LONG PRESS BEGAN");
            break;

        case UIGestureRecognizerState.Ended:
            System.Diagnostics.Debug.WriteLine("LONG PRESS ENDED");
            break;
    }
}