添加Xamarin形式的长按手势识别器

Question

您能告诉我如何在Xamarin Forms应用程序中识别长按手势吗？

这是我创建的xaml页面，它引用了以下线程：Xamarin.forms.DataGrid

<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
xmlns:local="clr-namespace:DataGridSample_01"
xmlns:dg="clr-namespace:Xamarin.Forms.DataGrid;assembly=Xamarin.Forms.DataGrid"
x:Class="DataGridSample_01.MainPage">
<ContentView BackgroundColor="White" Padding="20" >
<dg:DataGrid ItemsSource="{Binding Data}" SelectionEnabled="True" RowHeight="70" HeaderHeight="50" BorderColor="#CCCCCC" HeaderBackground="#E0E6F8" ActiveRowColor="#8899AA">
<dg:DataGrid.Columns>
<dg:DataGridColumn Title="Logo" PropertyName="Logo" Width="50" SortingEnabled="False">
<dg:DataGridColumn.CellTemplate>
<DataTemplate>
<Image Source="{Binding}" HorizontalOptions="Center" VerticalOptions="Center" Aspect="AspectFit" HeightRequest="60" />
</DataTemplate>
</dg:DataGridColumn.CellTemplate>
</dg:DataGridColumn>
<dg:DataGridColumn Title="Team" PropertyName="Name" Width="2*" >
</dg:DataGridColumn>
<dg:DataGridColumn Title="Win" PropertyName="Win" Width="2*">
<dg:DataGridColumn.CellTemplate>
<DataTemplate>
<Picker x:Name="Fruits" Title="Fruits" HorizontalOptions="FillAndExpand">
<Picker.Items>
<x:String>Apple</x:String>
<x:String>Mango</x:String>
<x:String>PineApple</x:String>
<x:String>Orange</x:String>
</Picker.Items>
</Picker>
</DataTemplate>
</dg:DataGridColumn.CellTemplate>
</dg:DataGridColumn>
<dg:DataGridColumn Title="Loose" PropertyName="Loose"  Width="1*">                    
</dg:DataGridColumn>
<dg:DataGridColumn PropertyName="Home">
<dg:DataGridColumn.FormattedTitle>
<FormattedString>
<Span Text="Home" ForegroundColor="Black" FontSize="13" FontAttributes="Bold"/>
<Span Text=" (win-loose)" ForegroundColor="#333333" FontSize="11" />
</FormattedString>
</dg:DataGridColumn.FormattedTitle>
</dg:DataGridColumn>
<dg:DataGrid.RowsBackgroundColorPalette>
<dg:PaletteCollection>
<Color>#FFFFFF</Color>
</dg:PaletteCollection>
</dg:DataGrid.RowsBackgroundColorPalette>
</dg:DataGrid>
</ContentView>
</ContentPage>

我想在图像控制上添加一个长按手势识别器。我试着参考这个StackOverflow线程来做。但它似乎不起作用。

我对此很陌生。非常感谢您的帮助。

Answer 1

不再需要定义自己的效果，因为TouchEffect已经存在于Xamarin Community Toolkit包中(该包收集了许多很酷的可重复使用/通用控件、效果、行为、转换器…(。

xaml命名空间：

xmlns:xct="http://xamarin.com/schemas/2020/toolkit"

用法示例

您可以设置触发命令所需的长按持续时间，也可以默认为500ms。在本例中，LongPressCommand将在2秒钟后被激发/触发。

<Image Source="{Binding}" HorizontalOptions="Center" VerticalOptions="Center"
Aspect="AspectFit" HeightRequest="60"
xct:TouchEffect.LongPressCommand="{Binding LongPressCommand}"
xct:TouchEffect.LongPressDuration="2000"/>

ICommand LongPressCommand = new Command(() =>
{
LongPressCount++;
OnPropertyChanged(nameof(LongPressCount));
});

此外，与CommandParameter相同，您有一个可选的LongPressCommandParameter，可以在其中将自定义参数绑定到命令。

资源

文档(正在工作中(https://learn.microsoft.com/en-us/xamarin/community-toolkit/

回购https://github.com/xamarin/XamarinCommunityToolkit/

https://www.youtube.com/watch?v=BcFlZMhPmVk

Answer 2

您可以使用Effect将LongPressGestureRecognizer添加到任何控件中。

在表单中，创建一个新的共享效果。

using System;
using System.Windows.Input;
using Xamarin.Forms;
namespace App15
{
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)
{
//do something you want 
Console.WriteLine("long press Gesture recognizer has been striked");

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);
}
}
}

在安卓项目

using System;
using Xamarin.Forms;
using Xamarin.Forms.Platform.Android;
using App15;
using App15.Droid;    
[assembly: ResolutionGroupName("MyApp")]
[assembly: ExportEffect(typeof(AndroidLongPressedEffect), "LongPressedEffect")]
namespace AndroidAppNamespace.Effects
{
public class AndroidLongPressedEffect : PlatformEffect
{
private bool _attached;
public static void Initialize() { }
public AndroidLongPressedEffect()
{
}
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;
}
}

// Invoke the command if there is one
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));
}

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项目

using Foundation;
using UIKit;
using App15;
using App15.iOS;
using Xamarin.Forms;
using Xamarin.Forms.Platform.iOS;
[assembly: ResolutionGroupName("MyApp")]
[assembly: ExportEffect(typeof(iOSLongPressedEffect), "LongPressedEffect")]
namespace App15.iOS
{
public class iOSLongPressedEffect : PlatformEffect
{
private bool _attached;
private readonly UILongPressGestureRecognizer _longPressRecognizer;
public iOSLongPressedEffect()
{
_longPressRecognizer = new UILongPressGestureRecognizer(HandleLongClick);
}

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;
}
}

// Invoke the command if there is one       
private void HandleLongClick(UILongPressGestureRecognizer sender)
{
if(sender.State==UIGestureRecognizerState.Began)
{
var command = LongPressedEffect.GetCommand(Element);
command?.Execute(LongPressedEffect.GetCommandParameter(Element));
}

}
protected override void OnDetached()
{
if (_attached)
{
Container.RemoveGestureRecognizer(_longPressRecognizer);
_attached = false;
}
}
}
}

现在，您可以将LongPressGestureRecognizer添加到控件中。例如标签或图像。

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

有关效果的更多详细信息，您可以参考这里的