我希望当按钮按下和释放时，我的事件能够被触发，但在Xamarin.Forms中我只找到了点击事件。
我相信一定有一些解决方法可以实现这个功能。我基本的需求是在按钮按下时启动一个进程，在释放时停止。这似乎是一个非常基本的功能，但是目前Xamarin.Forms没有它。
我尝试了在按钮上使用TapGestureRecognizer，但是按钮仅触发了点击事件。
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，我需要这些事件在Android和iOS上同时正常工作。
最终我得到了@Jason建议的解决方案。下面是具体步骤：
在PCL项目中创建Xamarin.Forms.Button的子类，具有事件处理能力
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特定平台的按钮渲染器
对于安卓
[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();
}
};
}
}
}
适用于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();
};
}
}
}
在你的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");
};
希望这对某些人有所帮助 :)
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);
}
}
[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;
}
}
}
}
[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;
}
}
}
}
<Label Text="Long Press Me!" effects:LongPressedEffect.Command="{Binding ShowAlertCommand}" effects:LongPressedEffect.CommandParameter="{Binding .}">
<Label.Effects>
<effects:LongPressedEffect />
</Label.Effects>
</Label>
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();
}
};
Forms项目中（在特定于平台的项目中不需要）。<StackLayout>
<StackLayout.Effects>
<tt:TouchEffect TouchAction="Handle_TouchAction" />
</StackLayout.Effects>
<Label Text="Sample"/>
</StackLayout>
使用tt表示：
xmlns:tt="clr-namespace:TouchTracking.Forms;assembly=TouchTracking.Forms"
void Handle_TouchAction(object sender, TouchTracking.TouchActionEventArgs args)
{
;
}
Handle_TouchAction会在每次触摸操作发生时被调用，使用args.Type来区分Pressed、Released、Exited等动作。
注意：Effects可用于各种组件，不仅限于StackLayout。