能告诉我如何识别Xamarin Forms应用程序中的长按手势？
我用TapGestureRecognizer前几天
TapGestureRecognizer imageTap = new TapGestureRecognizer();
imageTap.Tapped += (sender, args) => this.OnClickImage;
image.GestureRecognizers.Add(imageTap);
但根据这个thread from xamarin forum，我不知道如何做长按手势
它应该看起来像这样，但它不起作用。
var dumpParam = new RelayGesture((g, x) => DisplayAlert("Title", "Hello message", "Cancel"));
book.Cover.SetValue(Gestures.InterestsProperty, new GestureCollection() {
new GestureInterest
{
GestureType = GestureType.LongPress
GestureCommand = // what should I set?
GestureParameter = dumpParam
}
});
如何设置我的自定义处理程序方法？
您可以通过附加以下行为来跨平台方式进行，只要它是Xamarin.Forms.Button或它的子类型。
using System;
using System.Threading;
using System.Windows.Input;
using Xamarin.Forms;
namespace App.Controls.Behaviors
{
public class LongPressBehavior : Behavior<Button>
{
private readonly object _syncObject = new object();
private const int Duration = 1000;
//timer to track long press
private Timer _timer;
//the timeout value for long press
private readonly int _duration;
//whether the button was released after press
private volatile bool _isReleased;
/// <summary>
/// Occurs when the associated button is long pressed.
/// </summary>
public event EventHandler LongPressed;
public static readonly BindableProperty CommandProperty = BindableProperty.Create(nameof(Command),
typeof(ICommand), typeof(LongPressBehavior), default(ICommand));
public static readonly BindableProperty CommandParameterProperty =
BindableProperty.Create(nameof(CommandParameter), typeof(object), typeof(LongPressBehavior));
/// <summary>
/// Gets or sets the command parameter.
/// </summary>
public object CommandParameter
{
get => GetValue(CommandParameterProperty);
set => SetValue(CommandParameterProperty, value);
}
/// <summary>
/// Gets or sets the command.
/// </summary>
public ICommand Command
{
get => (ICommand)GetValue(CommandProperty);
set => SetValue(CommandProperty, value);
}
protected override void OnAttachedTo(Button button)
{
base.OnAttachedTo(button);
this.BindingContext = button.BindingContext;
button.Pressed += Button_Pressed;
button.Released += Button_Released;
}
protected override void OnDetachingFrom(Button button)
{
base.OnDetachingFrom(button);
this.BindingContext = null;
button.Pressed -= Button_Pressed;
button.Released -= Button_Released;
}
/// <summary>
/// DeInitializes and disposes the timer.
/// </summary>
private void DeInitializeTimer()
{
lock (_syncObject)
{
if (_timer == null)
{
return;
}
_timer.Change(Timeout.Infinite, Timeout.Infinite);
_timer.Dispose();
_timer = null;
Debug.WriteLine("Timer disposed...");
}
}
/// <summary>
/// Initializes the timer.
/// </summary>
private void InitializeTimer()
{
lock (_syncObject)
{
_timer = new Timer(Timer_Elapsed, null, _duration, Timeout.Infinite);
}
}
private void Button_Pressed(object sender, EventArgs e)
{
_isReleased = false;
InitializeTimer();
}
private void Button_Released(object sender, EventArgs e)
{
_isReleased = true;
DeInitializeTimer();
}
protected virtual void OnLongPressed()
{
var handler = LongPressed;
handler?.Invoke(this, EventArgs.Empty);
if (Command != null && Command.CanExecute(CommandParameter))
{
Command.Execute(CommandParameter);
}
}
public LongPressBehavior()
{
_isReleased = true;
_duration = Duration;
}
public LongPressBehavior(int duration) : this()
{
_duration = duration;
}
private void Timer_Elapsed(object state)
{
DeInitializeTimer();
if (_isReleased)
{
return;
}
Device.BeginInvokeOnMainThread(OnLongPressed);
}
}
}
在XAML UI中：
<Button x:Name="MyButton" Text="Long Press Me!">
<Button.Behaviors>
<behaviors:LongPressBehavior LongPressed="MyButton_LongPressed"/>
</Button.Behaviors>
</Button>
带命令绑定的XAML UI：
<Button x:Name="MyButton" Text="Long Press Me!">
<Button.Behaviors>
<behaviors:LongPressBehavior Command="{Binding CommandInViewModel}"/>
</Button.Behaviors>
</Button>
上网冲浪我找到了解决方案。您应该重现几个步骤。
1）继承你需要手势的控件（即如果你想向Xamarin.Forms.Image添加手势，创建你自己的ImageWithLongPressGesture类）。
public class ImageWithLongPressGesture : Xamarin.Forms.Image
{
public EventHandler LongPressActivated;
public void HandleLongPress(object sender, EventArgs e)
{
//Handle LongPressActivated Event
}
}
2）公开所需手势的公共事件。
3）为每个平台创建一个渲染器。
4）在渲染器中，处理手势并将它们冒泡到控件中。
[assembly: ExportRenderer(typeof(ImageWithLongPressGesture), typeof(LongPressGestureRecognizerImageRenderer))]
namespace App1.Droid.DroidRenderers
{
public class LongPressGestureRecognizerImageRenderer : ImageRenderer
{
ImageWithLongPressGesture view;
public LongPressGestureRecognizerImageRenderer()
{
this.LongClick += (sender, args) => {
Toast.MakeText(this.Context, "Long press is activated.", ToastLength.Short).Show();
};
}
protected override void OnElementChanged(ElementChangedEventArgs<Image> e)
{
base.OnElementChanged(e);
if(e.NewElement != null)
{
view = e.NewElement as ImageWithLongPressGesture;
}
}
}
}
这个解决方案是Telerik的answer on xamarin forms forum和Touch and Gestures presentation的混合体。
使用XLabs.Forms nuget包，它只能在PCL代码中进行长按和其他手势。使用XLabs.Forms包将减少在各个平台上自定义呈现的需要...在.xaml文件中添加XAML代码并在.xaml.cs文件中添加附加事件处理程序..它在Android中正常工作..
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
x:Class="MultiImage.Page1"
xmlns:lc="clr-namespace:XLabs.Forms.Controls;assembly=XLabs.Forms"
xmlns:lb="clr-namespace:XLabs.Forms.Behaviors;assembly=XLabs.Forms">
<ContentPage.Content>
<lc:GesturesContentView ExcludeChildren="False" GestureRecognized="GesturesContentView_GestureRecognized">
<lb:Gestures.Interests>
<lb:GestureCollection>
<lb:GestureInterest GestureType="SingleTap"/>
<lb:GestureInterest GestureType="LongPress"/>
<lb:GestureInterest GestureType="DoubleTap"/>
</lb:GestureCollection>
</lb:Gestures.Interests>
<Image Source="Myimage.png" Aspect="AspectFit" HeightRequest="100"/>
</lc:GesturesContentView>
</ContentPage.Content>
C＃后端代码：
private void GesturesContentView_GestureRecognized(object sender, GestureResult e)
{
switch (e.GestureType)
{
case GestureType.LongPress:
//Add code here
break;
case GestureType.SingleTap:
// Add code here
break;
case GestureType.DoubleTap:
// Add code here
break;
default:
break;
}
我最近遇到了这个问题，发现了一个关于https://alexdunn.org/2017/12/27/xamarin-tip-xamarin-forms-long-press-effect/主题的有用帖子
这使用了RoutingEffect，并通过一个如何创建iOS和Android实现的示例。这种简单性允许您将其附加到应用程序中的任何视图，而无需重新创建代码。
//To Add Programatically:
StackLayout _Containter = new StackLayout();
StackLayout _StackLayout = new StackLayout();
_StackLayout.Children.Add(new Label(){Text="Execute Me"});
GesturesContentView Gv = new GesturesContentView();
_StackLayout.SetValue(XLabs.Forms.Behaviors.Gestures.InterestsProperty, new GestureCollection() {
new GestureInterest() { GestureType = GestureType.SingleTap },
new GestureInterest() { GestureType = GestureType.LongPress },
new GestureInterest() { GestureType = GestureType.DoubleTap }
});
Gv.GestureRecognized += Gv_GestureRecognized;
Gv.ExcludeChildren = false;
Gv.Content = _StackLayout;
_Containter.Children.Add(Gv);
为了使其在iOS上正常工作，您需要使用XLabs.Forms.XFormsAppiOS.Init（）;在LoadApplication（新的App（））之前的AppDelegate.cs文件中;声明。