Xamarin.Forms

Question

我希望我的事件在按钮 按下和释放 时触发，但我只能在 Xamarin.Forms 中找到 Click 事件].

我相信必须有一些解决方法才能获得此功能。我的基本需求是 按下按钮时启动进程，释放时停止 。这似乎是一个非常基本的功能，但 Xamarin.Forms 目前没有。

我在按钮上尝试了 TapGestureRecognizer，但按钮仅触发点击事件。

MyButton.Clicked += (sender, args) =>
{
  Log.V(TAG, "CLICKED");
};

var tapGestureRecognizer = new TapGestureRecognizer();
tapGestureRecognizer.Tapped += (s, e) => {
    Log.V(TAG, "TAPPED");
};
MyButton.GestureRecognizers.Add(tapGestureRecognizer);

请记住，我需要这些事件在 Android 和 iOS 中一起工作。

Answer 1

终于得到了@Jason建议的解决方案。我们开始...

在 PCL 项目中创建 Xamarin.Forms.Button 的子 class，带有事件处理能力

public class CustomButton : Button
{
    public event EventHandler Pressed;
    public event EventHandler Released;

    public virtual void OnPressed()
    {
      Pressed?.Invoke(this, EventArgs.Empty);
    }

    public virtual void OnReleased()
    {
      Released?.Invoke(this, EventArgs.Empty);
    }
}

在各自的项目中创建平台特定的按钮渲染器

安卓版

[assembly: ExportRenderer(typeof(Button), typeof(CustomButtonRenderer))]
namespace WalkieTalkie.Droid.Renderer
{
    public class CustomButtonRenderer : ButtonRenderer
    {
        protected override void OnElementChanged(ElementChangedEventArgs<Xamarin.Forms.Button> e)
        {
            base.OnElementChanged(e);

            var customButton = e.NewElement as CustomButton;

            var thisButton = Control as Android.Widget.Button;
            thisButton.Touch += (object sender, TouchEventArgs args) =>
            {
                if (args.Event.Action == MotionEventActions.Down)
                {
                    customButton.OnPressed();
                }
                else if (args.Event.Action == MotionEventActions.Up)
                {
                    customButton.OnReleased();
                }
            };
        }
    }
}

对于IOS

[assembly: ExportRenderer(typeof(CustomButton), typeof(CustomButtonRenderer))]
namespace WalkieTalkie.iOS.Renderer
{
    public class CustomButtonRenderer : ButtonRenderer
    {
        protected override void    OnElementChanged(ElementChangedEventArgs<Xamarin.Forms.Button> e)
        {
            base.OnElementChanged(e);

            var customButton = e.NewElement as CustomButton;

            var thisButton = Control as UIButton;
            thisButton.TouchDown += delegate
            {
                customButton.OnPressed();
            };
            thisButton.TouchUpInside += delegate
            {
                customButton.OnReleased();
            };
        }
    }
}

在您的页面中实例化您的自定义按钮

var myButton = new CustomButton
{
    Text = "CustomButton",
    HorizontalOptions = LayoutOptions.FillAndExpand
};
myButton.Pressed += (sender, args) =>
{
    System.Diagnostics.Debug.WriteLine("Pressed");
};
myButton.Released += (sender, args) =>
{
     System.Diagnostics.Debug.WriteLine("Pressed");
};

希望这对某人有所帮助:)

Answer 2

Button button = FindViewById (Resource.Id.myButton);
button.Touch += (object sender, View.TouchEventArgs e) =>
{
if (e.Event.Action == MotionEventActions.Up)
{
Toast.MakeText(this, "Key Up", ToastLength.Short).Show();
}
        if(e.Event.Action == MotionEventActions.Down)
        {
            Toast.MakeText(this, "Key Down", ToastLength.Short).Show();
        }
    };

Answer 3

这也可以通过效果而不是完整的自定义渲染器来完成。请参阅此 post 以了解如何操作：

https://alexdunn.org/2017/12/27/xamarin-tip-xamarin-forms-long-press-effect/

以防 post 消失，这里是您可以实现的代码：

In shared project:

/// <summary>
/// Long pressed effect. Used for invoking commands on long press detection cross platform
/// </summary>
public class LongPressedEffect : RoutingEffect
{
    public LongPressedEffect() : base("MyApp.LongPressedEffect")
    {
    }

    public static readonly BindableProperty CommandProperty = BindableProperty.CreateAttached("Command", typeof(ICommand), typeof(LongPressedEffect), (object)null);
    public static ICommand GetCommand(BindableObject view)
    {
        return (ICommand)view.GetValue(CommandProperty);
    }

    public static void SetCommand(BindableObject view, ICommand value)
    {
        view.SetValue(CommandProperty, value);
    }


    public static readonly BindableProperty CommandParameterProperty = BindableProperty.CreateAttached("CommandParameter", typeof(object), typeof(LongPressedEffect), (object)null);
    public static object GetCommandParameter(BindableObject view)
    {
        return view.GetValue(CommandParameterProperty);
    }

    public static void SetCommandParameter(BindableObject view, object value)
    {
        view.SetValue(CommandParameterProperty, value);
    }
}

In Android:

[assembly: ResolutionGroupName("MyApp")]
[assembly: ExportEffect(typeof(AndroidLongPressedEffect), "LongPressedEffect")]
namespace AndroidAppNamespace.Effects
{
    /// <summary>
    /// Android long pressed effect.
    /// </summary>
    public class AndroidLongPressedEffect : PlatformEffect
    {
        private bool _attached;

        /// <summary>
        /// Initializer to avoid linking out
        /// </summary>
        public static void Initialize() { }

        /// <summary>
        /// Initializes a new instance of the
        /// <see cref="T:Yukon.Application.AndroidComponents.Effects.AndroidLongPressedEffect"/> class.
        /// Empty constructor required for the odd Xamarin.Forms reflection constructor search
        /// </summary>
        public AndroidLongPressedEffect()
        {
        }

        /// <summary>
        /// Apply the handler
        /// </summary>
        protected override void OnAttached()
        {
            //because an effect can be detached immediately after attached (happens in listview), only attach the handler one time.
            if (!_attached)
            {
                if (Control != null)
                {
                    Control.LongClickable = true;
                    Control.LongClick += Control_LongClick;
                }
                else
                {
                    Container.LongClickable = true;
                    Container.LongClick += Control_LongClick;
                }
                _attached = true;
            }
        }

        /// <summary>
        /// Invoke the command if there is one
        /// </summary>
        /// <param name="sender">Sender.</param>
        /// <param name="e">E.</param>
        private void Control_LongClick(object sender, Android.Views.View.LongClickEventArgs e)
        {
            Console.WriteLine("Invoking long click command");
            var command = LongPressedEffect.GetCommand(Element);
            command?.Execute(LongPressedEffect.GetCommandParameter(Element));
        }

        /// <summary>
        /// Clean the event handler on detach
        /// </summary>
        protected override void OnDetached()
        {
            if (_attached)
            {
                if (Control != null)
                {
                    Control.LongClickable = true;
                    Control.LongClick -= Control_LongClick;
                }
                else
                {
                    Container.LongClickable = true;
                    Container.LongClick -= Control_LongClick;
                }
                _attached = false;
            }
        }
    }
}

In iOS:

[assembly: ResolutionGroupName("MyApp")]
[assembly: ExportEffect(typeof(iOSLongPressedEffect), "LongPressedEffect")]
namespace iOSNamespace.Effects
{
    /// <summary>
    /// iOS long pressed effect
    /// </summary>
    public class iOSLongPressedEffect : PlatformEffect
    {
        private bool _attached;
        private readonly UILongPressGestureRecognizer _longPressRecognizer;
        /// <summary>
        /// Initializes a new instance of the
        /// <see cref="T:Yukon.Application.iOSComponents.Effects.iOSLongPressedEffect"/> class.
        /// </summary>
        public iOSLongPressedEffect()
        {
            _longPressRecognizer = new UILongPressGestureRecognizer(HandleLongClick);
        }

        /// <summary>
        /// Apply the handler
        /// </summary>
        protected override void OnAttached()
        {
            //because an effect can be detached immediately after attached (happens in listview), only attach the handler one time
            if (!_attached)
            {
                Container.AddGestureRecognizer(_longPressRecognizer);
                _attached = true;
            }
        }

        /// <summary>
        /// Invoke the command if there is one
        /// </summary>
        private void HandleLongClick()
        {
            var command = LongPressedEffect.GetCommand(Element);
            command?.Execute(LongPressedEffect.GetCommandParameter(Element));
        }

        /// <summary>
        /// Clean the event handler on detach
        /// </summary>
        protected override void OnDetached()
        {
            if (_attached)
            {
                Container.RemoveGestureRecognizer(_longPressRecognizer);
                _attached = false;
            }
        }

    }
}

In XAML

<Label Text="Long Press Me!" effects:LongPressedEffect.Command="{Binding ShowAlertCommand}" effects:LongPressedEffect.CommandParameter="{Binding .}">
    <Label.Effects>
        <effects:LongPressedEffect />
    </Label.Effects>
</Label>

Answer 4

自 Xamarin.Forms 2.4.0，事件 Pressed and Released are offered out of the box (see PR).

注意：为了实现对讲机效果，您可能需要使用 Device.BeginInvokeOnMainThread（或通过 Prism 的 IDeviceService）调用后续操作，以便调用 Released 事件，否则 UI 线程可能会被阻塞。
或者，您可以将事件处理程序声明为 async 和 await 您的调用，以保持 UI 线程未被占用。

Answer 5

为了拦截 Xamarin 上的 Pressed 和 Released 事件，我使用了 Effects 属性，如 this official Guide 中所述。

使用TouchTracking.Forms更简单。

首先将库添加到您的 Forms 项目（平台特定项目不需要）。

接下来在 Xaml asis

中使用它

<StackLayout>
    <StackLayout.Effects>
        <tt:TouchEffect TouchAction="Handle_TouchAction" />
    </StackLayout.Effects>
    <Label Text="Sample"/>
</StackLayout>

与tt指的是：

xmlns:tt="clr-namespace:TouchTracking.Forms;assembly=TouchTracking.Forms"

最后在代码后面做你的逻辑:

void Handle_TouchAction(object sender, TouchTracking.TouchActionEventArgs args)
{
    ;
}

Handle_TouchAction会在每次触摸动作发生时被调用，使用args.Type区分动作Pressed,Released,Exited...

N.B Effects不仅可用于各种组件 StackLayout.

Xamarin.Forms - 按钮按下和释放事件

Xamarin.Forms - Button Pressed & Released Event

c#

events

cross-platform