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ApplicationCommands命令实战

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这一节我们来演示一下ApplicationCommands预定义命令的使用，通过一个建议的记事本开发流程，掌握ApplicationCommands预定义命令的用法。

使用预定义命令，最重要的三个地方，第一点，如何通过CommandBinding对象去关联一个Command，第二点，如何编写命令的业务代码，第三点，命令如何触发，或者说，命令如何绑定到命令源对象。

第一点，通过CommandBinding对象去关联一个Command

<Window.CommandBindings>
    <CommandBinding Command="ApplicationCommands.Open"  
                    CanExecute="OpenCommandCanExecute" 
                    Executed="OpenCommandExecuted"  />
    
    <CommandBinding Command="ApplicationCommands.Cut" 
                    CanExecute="CutCommandCanExecute" 
                    Executed="CutCommandExecuted" />
    
    <CommandBinding Command="ApplicationCommands.Paste" 
                    CanExecute="PasteCommandCanExecute" 
                    Executed="PasteCommandExecuted" />
    
    <CommandBinding Command="ApplicationCommands.Save"  
                    CanExecute="SaveCommandCanExecute" 
                    Executed="SaveCommandExecuted" />
</Window.CommandBindings>

在Window窗体的CommandBindings集合中，我们实例化了4个CommandBinding对象，分别关联了Open、Cut、Paste和Save，对应打开、剪切、粘贴和保存。

第二点，如何编写命令的业务代码

private void OpenCommandCanExecute(object sender, CanExecuteRoutedEventArgs e)
{
    e.CanExecute = true;
}

private void OpenCommandExecuted(object sender, ExecutedRoutedEventArgs e)
{
    var openFileDialog = new Microsoft.Win32.OpenFileDialog()
    {
        Filter = "文本文档 (.txt)|*.txt",
        Multiselect = true
    };
    var result = openFileDialog.ShowDialog();
    if (result.Value)
    {
        textbox.Text = File.ReadAllText(openFileDialog.FileName);
    }
}

private void CutCommandCanExecute(object sender, CanExecuteRoutedEventArgs e)
{
    e.CanExecute = textbox != null && textbox.SelectionLength > 0;
}

private void CutCommandExecuted(object sender, ExecutedRoutedEventArgs e)
{
    textbox.Cut();
}

private void PasteCommandCanExecute(object sender, CanExecuteRoutedEventArgs e)
{
    e.CanExecute = Clipboard.ContainsText();
}

private void PasteCommandExecuted(object sender, ExecutedRoutedEventArgs e)
{
    textbox.Paste();
}

private void SaveCommandCanExecute(object sender, CanExecuteRoutedEventArgs e)
{
    e.CanExecute = textbox != null && textbox.Text.Length > 0;
}

private void SaveCommandExecuted(object sender, ExecutedRoutedEventArgs e)
{
    var saveFileDialog = new Microsoft.Win32.SaveFileDialog
    {
        Filter = "文本文档 (.txt)|*.txt"
    };

    if (saveFileDialog.ShowDialog() == true)
    {
        File.WriteAllText(saveFileDialog.FileName , textbox.Text);
    }
}

我们需要给Command的CanExecute和Executed成员分别创建各自的回调函数，并在函数中编写自己的业务逻辑。

第三点，命令如何绑定到命令源对象

绑定命令的方式通常是通过控件的事件、或者响应键盘或鼠标的操作去实现的，在这里，我们演示这两种方法，第一种是通过快捷键去绑定上面的命令。

<Window.InputBindings>
    <KeyBinding Key="O" Modifiers="Control" Command="ApplicationCommands.Open" />
    <KeyBinding Key="X" Modifiers="Control" Command="ApplicationCommands.Cut" />
    <KeyBinding Key="V" Modifiers="Control" Command="ApplicationCommands.Paste" />
    <KeyBinding Key="S" Modifiers="Control" Command="ApplicationCommands.Save" />
</Window.InputBindings>

这些KeyBinding可以定义快捷键，并指向某个命令。第二种方式就是创建一个前端控件，比如实例化一个按钮，利用按钮的Command绑定命令。

<Grid>
    <Grid.RowDefinitions>
        <RowDefinition Height="auto"/>
        <RowDefinition/>
    </Grid.RowDefinitions>
    <StackPanel Orientation="Horizontal">
        <Button Content="打开" Margin="5" Command="ApplicationCommands.Open"/>
        <Button Content="剪切" Margin="5" Command="ApplicationCommands.Cut"/>
        <Button Content="粘贴" Margin="5" Command="ApplicationCommands.Paste"/>
        <Button Content="保存" Margin="5" Command="ApplicationCommands.Save"/>
    </StackPanel>
    <TextBox x:Name="textbox" Grid.Row="1" Margin="5" TextWrapping="Wrap">
        
    </TextBox>
</Grid>

坦白说，WPF的预定义命令并不常用，但是作为开发者，还是很有必要全面了解一下相关知识。我们更多时候还是使用ICommand的自定义命令，下一讲，我们将介绍控件的其它事件如何去引用一个命令。

当前课程源码下载：（注明：本站所有源代码请按标题搜索）

文件名：071-《ApplicationCommands与记事本开发实战》-源代码
链接：https://pan.baidu.com/s/1yu-q4tUtl0poLVgmcMfgBA
提取码：wpff

——重庆教主 2023年10月12日

WPF 提供一组预定义命令。命令库包括以下类：ApplicationCommands、NavigationCommands、MediaCommands、EditingCommands 和 ComponentCommands。 这些类提供诸如 Cut、BrowseBack、BrowseForward、Play、Stop 和 Pause 的命令。这些类仅由 RoutedCommand 对象构成，而不包含命令的实现逻辑。 实现逻辑由在其上执行命令的对象负责。

我们来看看这几个类的定义。

一、ApplicationCommands的定义

public static class ApplicationCommands
{
    public static RoutedUICommand Cut { get; }
    public static RoutedUICommand Stop { get; }
    public static RoutedUICommand ContextMenu { get; }
    public static RoutedUICommand Properties { get; }
    public static RoutedUICommand PrintPreview { get; }
    public static RoutedUICommand CancelPrint { get; }
    public static RoutedUICommand Print { get; }
    public static RoutedUICommand SaveAs { get; }
    public static RoutedUICommand Save { get; }
    public static RoutedUICommand Close { get; }
    public static RoutedUICommand CorrectionList { get; }
    public static RoutedUICommand Open { get; }
    public static RoutedUICommand Help { get; }
    public static RoutedUICommand SelectAll { get; }
    public static RoutedUICommand Replace { get; }
    public static RoutedUICommand Find { get; }
    public static RoutedUICommand Redo { get; }
    public static RoutedUICommand Undo { get; }
    public static RoutedUICommand Delete { get; }
    public static RoutedUICommand Paste { get; }
    public static RoutedUICommand Copy { get; }
    public static RoutedUICommand New { get; }
    public static RoutedUICommand NotACommand { get; }

}

二、NavigationCommands 的定义

public static class NavigationCommands
{
    public static RoutedUICommand BrowseBack { get; }
    public static RoutedUICommand BrowseForward { get; }
    public static RoutedUICommand BrowseHome { get; }
    public static RoutedUICommand BrowseStop { get; }
    public static RoutedUICommand Refresh { get; }
    public static RoutedUICommand Favorites { get; }
    public static RoutedUICommand Search { get; }
    public static RoutedUICommand IncreaseZoom { get; }
    public static RoutedUICommand DecreaseZoom { get; }
    public static RoutedUICommand Zoom { get; }
    public static RoutedUICommand NextPage { get; }
    public static RoutedUICommand PreviousPage { get; }
    public static RoutedUICommand FirstPage { get; }
    public static RoutedUICommand LastPage { get; }
    public static RoutedUICommand GoToPage { get; }
    public static RoutedUICommand NavigateJournal { get; }

}

三、MediaCommands的定义

public static class MediaCommands
{
    public static RoutedUICommand Play { get; }
    public static RoutedUICommand DecreaseMicrophoneVolume { get; }
    public static RoutedUICommand IncreaseMicrophoneVolume { get; }
    public static RoutedUICommand BoostBass { get; }
    public static RoutedUICommand DecreaseBass { get; }
    public static RoutedUICommand IncreaseBass { get; }
    public static RoutedUICommand DecreaseTreble { get; }
    public static RoutedUICommand IncreaseTreble { get; }
    public static RoutedUICommand MuteVolume { get; }
    public static RoutedUICommand DecreaseVolume { get; }
    public static RoutedUICommand IncreaseVolume { get; }
    public static RoutedUICommand Select { get; }
    public static RoutedUICommand TogglePlayPause { get; }
    public static RoutedUICommand ChannelDown { get; }
    public static RoutedUICommand ChannelUp { get; }
    public static RoutedUICommand Rewind { get; }
    public static RoutedUICommand FastForward { get; }
    public static RoutedUICommand PreviousTrack { get; }
    public static RoutedUICommand NextTrack { get; }
    public static RoutedUICommand Record { get; }
    public static RoutedUICommand Stop { get; }
    public static RoutedUICommand Pause { get; }
    public static RoutedUICommand MuteMicrophoneVolume { get; }
    public static RoutedUICommand ToggleMicrophoneOnOff { get; }

}

四、EditingCommands的定义

public static class EditingCommands
{
public static RoutedUICommand ToggleInsert { get; }
public static RoutedUICommand SelectDownByParagraph { get; }
public static RoutedUICommand SelectUpByParagraph { get; }
public static RoutedUICommand SelectDownByPage { get; }
public static RoutedUICommand SelectUpByPage { get; }
public static RoutedUICommand SelectToLineStart { get; }
public static RoutedUICommand SelectToLineEnd { get; }
public static RoutedUICommand SelectToDocumentStart { get; }
public static RoutedUICommand SelectToDocumentEnd { get; }
public static RoutedUICommand ToggleBold { get; }
public static RoutedUICommand ToggleItalic { get; }
public static RoutedUICommand ToggleUnderline { get; }
public static RoutedUICommand ToggleSubscript { get; }
public static RoutedUICommand ToggleSuperscript { get; }
public static RoutedUICommand IncreaseFontSize { get; }
public static RoutedUICommand DecreaseFontSize { get; }
public static RoutedUICommand AlignLeft { get; }
public static RoutedUICommand AlignCenter { get; }
public static RoutedUICommand AlignRight { get; }
public static RoutedUICommand AlignJustify { get; }
public static RoutedUICommand ToggleBullets { get; }
public static RoutedUICommand ToggleNumbering { get; }
public static RoutedUICommand IncreaseIndentation { get; }
public static RoutedUICommand DecreaseIndentation { get; }
public static RoutedUICommand SelectUpByLine { get; }
public static RoutedUICommand SelectDownByLine { get; }
public static RoutedUICommand SelectLeftByWord { get; }
public static RoutedUICommand SelectRightByWord { get; }
public static RoutedUICommand Delete { get; }
public static RoutedUICommand Backspace { get; }
public static RoutedUICommand DeleteNextWord { get; }
public static RoutedUICommand DeletePreviousWord { get; }
public static RoutedUICommand EnterParagraphBreak { get; }
public static RoutedUICommand EnterLineBreak { get; }
public static RoutedUICommand TabForward { get; }
public static RoutedUICommand TabBackward { get; }
public static RoutedUICommand MoveRightByCharacter { get; }
public static RoutedUICommand MoveLeftByCharacter { get; }
public static RoutedUICommand MoveRightByWord { get; }
public static RoutedUICommand CorrectSpellingError { get; }
public static RoutedUICommand MoveLeftByWord { get; }
public static RoutedUICommand MoveUpByLine { get; }
public static RoutedUICommand MoveDownByParagraph { get; }
public static RoutedUICommand MoveUpByParagraph { get; }
public static RoutedUICommand MoveDownByPage { get; }
public static RoutedUICommand MoveUpByPage { get; }
public static RoutedUICommand MoveToLineStart { get; }
public static RoutedUICommand MoveToLineEnd { get; }
public static RoutedUICommand MoveToDocumentStart { get; }
public static RoutedUICommand MoveToDocumentEnd { get; }
public static RoutedUICommand SelectRightByCharacter { get; }
public static RoutedUICommand SelectLeftByCharacter { get; }
public static RoutedUICommand MoveDownByLine { get; }
public static RoutedUICommand IgnoreSpellingError { get; }

}

五、ComponentCommands的定义

public static class ComponentCommands
{
public static RoutedUICommand ScrollPageUp { get; }
public static RoutedUICommand MoveFocusBack { get; }
public static RoutedUICommand MoveFocusForward { get; }
public static RoutedUICommand MoveFocusDown { get; }
public static RoutedUICommand MoveFocusUp { get; }
public static RoutedUICommand SelectToPageDown { get; }
public static RoutedUICommand SelectToPageUp { get; }
public static RoutedUICommand SelectToEnd { get; }
public static RoutedUICommand SelectToHome { get; }
public static RoutedUICommand ExtendSelectionRight { get; }
public static RoutedUICommand ExtendSelectionLeft { get; }
public static RoutedUICommand ExtendSelectionDown { get; }
public static RoutedUICommand MoveFocusPageUp { get; }
public static RoutedUICommand ExtendSelectionUp { get; }
public static RoutedUICommand MoveToPageUp { get; }
public static RoutedUICommand MoveToEnd { get; }
public static RoutedUICommand MoveToHome { get; }
public static RoutedUICommand MoveDown { get; }
public static RoutedUICommand MoveUp { get; }
public static RoutedUICommand MoveRight { get; }
public static RoutedUICommand MoveLeft { get; }
public static RoutedUICommand ScrollByLine { get; }
public static RoutedUICommand ScrollPageRight { get; }
public static RoutedUICommand ScrollPageLeft { get; }
public static RoutedUICommand ScrollPageDown { get; }
public static RoutedUICommand MoveToPageDown { get; }
public static RoutedUICommand MoveFocusPageDown { get; }

}

这些命令都是RoutedUICommand类型，RoutedUICommand的父类是RoutedCommand，而RoutedCommand继承了ICommand接口。所以，本质上，RoutedUICommand也是一个ICommand对象。我们需要了解一下它的父类的定义 

public class RoutedCommand : ICommand
{
      public RoutedCommand();
      public RoutedCommand(string name, Type ownerType);
      public RoutedCommand(string name, Type ownerType, InputGestureCollection inputGestures);

      public string Name { get; }
      public Type OwnerType { get; }
      public InputGestureCollection InputGestures { get; }

      public event EventHandler CanExecuteChanged;

      public bool CanExecute(object parameter, IInputElement target);
      public void Execute(object parameter, IInputElement target);

}

这些预先定义好的命令并没有实现业务逻辑，如果要实现业务逻辑，需要用到CommandBinding对象。下一节，我们将介绍CommandBinding对象在命令与逻辑代码中间发挥了什么关键性的作用。

——重庆教主 2023年10月11日

copyright @重庆教主 WPF中文网 联系站长：（QQ）23611316 （微信）movieclip （QQ群）.NET小白课堂：864486030 | 本文由WPF中文网原创发布，谢绝转载 渝ICP备2023009518号-1