Xamarin.Forms - 按下按钮并释放事件

Question

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

我相信必须有一些工作来获得这个功能.我的基本需求是在按下按钮时启动一个过程,在释放按钮时停止.它似乎是一个非常基本的功能,但Xamarin.Forms现在没有它.

我在按钮上尝试了TapGestureRecognizer,但按钮只触发了点击事件.

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,我需要这些活动才能在Android和iOS中使用.

Answer 1

最后我得到了@Jason建议的解决方案.开始了...

1. 在PCL项目中创建Xamarin.Forms.Button的子类,具有事件处理功能

   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);
       }
   }
   

2. 在相应项目中创建特定于平台的按钮渲染器

   对于安道尔

   [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();
               };
           }
       }
   }
   

3. 在页面中实例化自定义按钮

   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");
   };
   

希望这能帮助别人:)

Answer 2

这也可以使用效果而不是完整的自定义渲染器来完成.有关如何操作的说明,请参阅此文章:

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

如果该帖子消失,这里是您可以实现的代码:

在共享项目中:

/// <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);
    }
}

在Android中:

[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;
            }
        }
    }
}

在iOS中:

[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;
            }
        }

    }
}

在XAML中

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

Answer 3

从 Xamarin.Forms 2.4.0 开始，事件Pressed和Released开箱即用（请参阅PR）。

注意：为了实现对讲机效果，您可能希望使用Device.BeginInvokeOnMainThread（或通过 Prism's IDeviceService）调用后续操作，以便调用该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。