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一、命令

官方文檔：https://learn.microsoft.com/zh-cn/dotnet/desktop/wpf/advanced/commanding-overview

1. ICommandSource

官方文檔：https://learn.microsoft.com/zh-cn/dotnet/desktop/wpf/advanced/how-to-implement-icommandsource

2. 示例

    <Grid><TextBox x:Name="textBox" Text="TextBox" VerticalAlignment="Top"  Height="150" Margin="219,35,187,0"/><Button x:Name="buttonCut"Content="剪切"Command="ApplicationCommands.Cut"CommandTarget="{Binding ElementName=textBox}"Height="100" Margin="219,233,419,102"/><Button x:Name="buttonPaste"Content="粘貼"Command="ApplicationCommands.Paste"CommandTarget="{Binding ElementName=textBox}" Margin="453,233,187,107"/></Grid>

3. CommandBinding

• 當TEXTBOX內容長度大于0時，CanExecute被判斷為true
• true可以啟用命令源按鈕，false禁用按鈕
  

<Window.CommandBindings><CommandBinding Command="ApplicationCommands.Cut" CanExecute="my_CanExecute" Executed="my_Execute"/>
</Window.CommandBindings><Grid><TextBox x:Name="textBox" Text="TextBox" VerticalAlignment="Top"  Height="150" Margin="219,35,187,0"/><Button x:Name="buttonCut" Margin="219,233,419,102" Height="100" Content="剪切"Command="ApplicationCommands.Cut"/><Button x:Name="buttonPaste"Content="粘貼"Command="ApplicationCommands.Paste"CommandTarget="{Binding ElementName=textBox}"Margin="453,233,187,107"/>
</Grid>

public partial class MainWindow : Window
{public MainWindow(){InitializeComponent();}private void my_Execute(object sender, ExecutedRoutedEventArgs e){Console.WriteLine("Execute!!!");textBox.Cut();}private void my_CanExecute(object sender, CanExecuteRoutedEventArgs e){e.CanExecute = textBox.SelectionLength > 0;}
}

二、ICommand

官方文檔：https://learn.microsoft.com/zh-cn/dotnet/api/system.windows.input.icommand?view=net-9.0

1.ICommand接口

ICommand接口的屬性與事件如下：

2. ICommand用法

    <Grid><TextBox HorizontalAlignment="Left" Margin="222,62,0,0" TextWrapping="Wrap" Text="TextBox" VerticalAlignment="Top" Width="422" Height="102"/><Button x:Name="button1" Content="  自定義命令" HorizontalAlignment="Left" Margin="222,217,0,0" VerticalAlignment="Top" Height="64" Width="145"/><Button x:Name="button2" Content="觸發事件" HorizontalAlignment="Left" Margin="499,217,0,0" VerticalAlignment="Top" Height="64" Width="145"/></Grid>

在MainWindow.xaml.cs文件內自定義命令接口

<Window.Resources><local:MyCommand x:Key="MyCMD" />
</Window.Resources>
<Grid><TextBox x:Name="textBox" HorizontalAlignment="Left" Margin="222,62,0,0" TextWrapping="Wrap" Text="TextBox" VerticalAlignment="Top" Width="422" Height="102"/><Button x:Name="button1" Content="  自定義命令"Command="{StaticResource MyCMD}"CommandParameter="{Binding ElementName=textBox,Path=Text}"HorizontalAlignment="Left" Margin="222,217,0,0" VerticalAlignment="Top" Height="64" Width="145"/><Button x:Name="button2" Content="觸發事件" HorizontalAlignment="Left" Margin="499,217,0,0" VerticalAlignment="Top" Height="64" Width="145"/>
</Grid>

public class MyCommand : ICommand
{public event EventHandler CanExecuteChanged;public bool CanExecute(object parameter){return true;//按鈕可以點擊//return false;//按鈕不可點擊}//Execute方法中實現命令處理邏輯public void Execute(object parameter){MessageBox.Show(parameter.ToString());}
}

以下為CanExecuteChanged的事件解釋：

public partial class MainWindow : Window
{public MainWindow(){InitializeComponent();}private void button2_Click(object sender, RoutedEventArgs e){MyCommand c = Resources["MyCMD"] as MyCommand;//觸發CanExecuteChangedc.RaiseCanExecuteChanged();}
}
//實現ICommand接口
public class MyCommand : ICommand
{public event EventHandler CanExecuteChanged;public bool CanExecute(object parameter){String str = parameter as String;return str?.Length > 0;//return true;//按鈕可以點擊//return false;//按鈕不可點擊}//Execute方法中實現命令處理邏輯public void Execute(object parameter){MessageBox.Show(parameter.ToString());}//定義一個方法，手動觸發CanExecuteChanged事件public void RaiseCanExecuteChanged() {//表面上，沒有為 CanExecuteChanged 這個事件添加任何訂閱方法//例如CanExecuteChanged += fun;//但是我們為按鈕設置命令時，自動加入了一個此事件訂閱的方法，//并且這個訂閱的方法，會去調用命令的CanExecute//可通過Delegate查看CanExecuteChanged的來源與內容Delegate[] delegates = CanExecuteChanged.GetInvocationList();//delegates內查看到 System.Windows.Input.CanExecuteChangedEventManager+HandlerSink"//OnCanExecuteChangedCanExecuteChanged?.Invoke(this, EventArgs.Empty);}

3. CanExecute

以ButtonBase為例介紹，調用了OnCommandChanged

OnCommandChanged調用了HookCommand

HookCommand調用了AddHandler，CanExecute調用了CanExecuteCommandSource

AddHandler調用的PrivateAddHandler又new 了一個HandlerSink

HandlerSink將OnCommandChanged函數添加到Icommand接口的CanExecuteChanged

總結

關于ButtonBase、CanExecuteChangedEventManager、commandHelpers的詳細原理、我們可以參考WPF框架的源碼
https://github.com/dotnet/wpf/blob/main/src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Controls/Primitives/ButtonBase.cs
https://github.com/dotnet/wpf/blob/main/src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Input/Command/CanExecuteRoutedEventArgs.cs
https://github.com/dotnet/wpf/blob/main/src/Microsoft.DotNet.Wpf/src/PresentationFramework/MS/Internal/Commands/CommandHelpers.cs