WPF-命令 | 易学教程

一、WPF为何需要命令

我们已经知道WPF里已经有了路由事件，可以发布及传播一些消息，那为什么还需要命令呢？这是因为事件指负责发送消息，对消息如何处理则不管，而命令是有约束力，每个接收者对命令执行统一的行为，比如菜单上的保存，工具栏上的保存都必须是执行同样的保存。

二、命令系统的基本元素

命令(Command)：实现了ICommand接口的类，经常使用的有RoutedCommand类

命令源: 是命令的发送者，是实现了ICommandSource接口的类，大部分界面的控件都实现了这个接口，Button, MenuItem 等等。

命令目标：命令的接收者，命令目标是视线了IInputElement接口的类。

命令关联：负责一些逻辑与命令关联起来，比如判断命令是否可以执行，以及执行完毕后做一些处理。

三、四个命令元素之间的关系

四、命令示例

我们让一个按钮发送Hello命令给文本框，文本框接收这个命令后显示“Nice to meet you”.

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<Window x:Class="DeepXAML.MainWindow"

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        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"

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        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"

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        xmlns:local="clr-namespace:DeepXAML"       

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        xmlns:sys="clr-namespace:System;assembly=mscorlib"

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        Title="MainWindow" Height="250" Width="450"> 

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    <StackPanel x:Name="stackPanel"> 

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        <TextBox x:Name="textBox1" Margin="10"></TextBox> 

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        <TextBox x:Name="textBox2" Margin="10"></TextBox> 

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        <Button x:Name="btnHello" Margin="10">Hello</Button> 

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    </StackPanel> 

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</Window>

后台代码

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using System; 

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using System.Collections.Generic; 

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using System.Windows; 

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using System.Windows.Data; 

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using System.Windows.Documents; 

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using System.Windows.Controls; 

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using System.Windows.Input; 

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namespace DeepXAML 

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{ 

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    public partial class MainWindow : Window 

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    { 

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        private RoutedCommand helloCmd = new RoutedCommand("Hello", typeof(MainWindow)); 

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        public MainWindow() 

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        { 

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            InitializeComponent(); 

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            this.btnHello.Command = this.helloCmd; 

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            this.helloCmd.InputGestures.Add(new KeyGesture(Key.H, ModifierKeys.Alt)); 

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            this.btnHello.CommandTarget = this.textBox1; 

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            this.btnHello.CommandTarget = this.textBox2; 

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            CommandBinding cb = new CommandBinding(); 

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            cb.Command = this.helloCmd; 

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            cb.CanExecute += new CanExecuteRoutedEventHandler(cb_CanExecute); 

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            cb.Executed += new ExecutedRoutedEventHandler(cb_Executed); 

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            this.stackPanel.CommandBindings.Add(cb); 

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        } 

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        void cb_Executed(object sender, ExecutedRoutedEventArgs e) 

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        {             

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            this.textBox1.Text = "Nice to meet you"; 

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            this.textBox2.Text = "Nice to meet you"; 

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            e.Handled = true; 

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        } 

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        void cb_CanExecute(object sender, CanExecuteRoutedEventArgs e) 

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        { 

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            if (!string.IsNullOrEmpty(textBox1.Text) || !string.IsNullOrEmpty(textBox2.Text)) 

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            { 

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              e.CanExecute=false; 

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            } 

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            else

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            { 

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                e.CanExecute = true; 

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            } 

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            // 避免继续传递 

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            e.Handled = true;             

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        } 

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    } 

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}

执行时

一开始按钮状态可用，也就是命令可执行

点击按钮后:

清空一个TextBox，按钮仍然不可执行，因为没达到可执行的条件，两个都清空时，按钮重回可执行状态

五、WPF的命令库

WPF提供常用应用程序所用的命令集，常用的命令集包括：ApplicationCommands, ComponentCommands, NavigationCommands, MediaCommands和EditingCommands。
ApplicationCommands（应用程序命令）:
CancelPrint:取消打印
Close：关闭
ContextMenu：上下文菜单
Copy：复制
CorrectionList： Gets the value that represents the Correction List command.
Cut：剪切
Delete：删除
Find：查找
Help：帮助
New：新建
NotACommand：不是命令，被忽略
Open：打开
Paste：粘贴
Print：打印
PrintPreview：打印预览
Properties：属性
Redo：重做
Replace：取代
Save：保存
SaveAs：另存为
SelectAll：选择所有的
Stop：停止
Undo：撤消
ComponentCommands（组件命令）:
ExtendSelection：后接Down/Left/Right/Up, 比如：ExtendSelectionDown（Shift+Down,Extend Selection Down)，ExtendSelectionLeft等
Move：后接Down/Left/Right/Up, 如：MoveDown
MoveFocus：后接Down/Forward/Back/Up, 如：MoveFocusDown
MoveFocusPage：后接Down/Up,如：MoveFocusPageUp
MoveTo：后接End/Home/PageDown/PageUp，比如：MoveToPageDown
ScrollByLine
ScrollPage：后接Down/Left/Right/Up，比如：ScrollPageLeft
SelectTo：End/Home/PageDown/PageUp，比如：SelectToEnd
NavigationCommands（导航命令）：
Browse浏览: 后接Back/Forward/Home/Stop, 比如：BrowseBack
缩放显示：DecreaseZoom, IncreaseZoom, Zoom
Favorites（收藏）
页面：FirstPage, LastPage, PreviousPage, NextPage,GoToPage
NavigateJournal
Refresh(刷新)
Search（搜索）
MediaCommands（多媒体控制命令）:
Treble高音：DecreaseTreble,IncreaseTreble
Bass低音:BoostBass,DecreaseBass,IncreaseBass
Channel频道：ChannelDown,ChannelUp
MicrophoneVolume麦克风音量调节:DecreaseMicrophoneVolume,IncreaseMicrophoneVolume,MuteMicrophoneVolume
ToggleMicrophoneOnOff:麦克风开关
Volume音量: DecreaseVolume,IncreaseVolume,MuteVolume
Rewind, FastForward(回放，快进)
Track轨道:PreviousTrack,NextTrack [上一段(节)]
Play,Pause,Stop,Record(播放，暂停，停止，录制)
TogglePlayPause
Select选择
EditingCommands（编辑/排版类命令）:
Align对齐：AlignCenter,AlignJustify,AlignLeft,AlignRight(居中，撑满，左对齐，右对齐)
Backspace退格
TabForward,TabBackward(Tab前缩，Tab向后)
FontSize字体大小：DecreaseFontSize,IncreaseFontSize
Indentation缩排：DecreaseIndentation, IncreaseIndentation
Delete删除: Delete选中部分，DeleteNextWord：删除后一字,DeletePreviousWord：删除前一字
EnterLineBreak：换行
EnterParagraphBreak：换段
CorrectSpellingError/IgnoreSpellingError：纠正/忽略拼写错误
MoveUpByLine,MoveDownByLine: 上/下移一行，
MoveUpByPage,MoveDownByPage: 上/下移一页
MoveUpByParagraph,MoveDownByParagraph: 上/下移一段
MoveLeftByCharacter/MoveRightByCharacter：左/右移一字符
MoveLeftByWord/MoveRightByWord 左/右移一词
MoveToDocumentStart/MoveToDocumentEnd:到文章开头/结尾
MoveToLineStart/MoveToLineEnd:到一行的开头/结尾
SelectUpByLine,SelectDownByLine：向上/下选一行
SelectUpByPage,SelectDownByPage：向上/下选一页
SelectUpByParagraph,SelectDownByParagraph：向上/下选一段
SelectLeftByCharacter,SelectRightByCharacter:向左/右选中一字
SelectLeftByWord,SelectRightByWord:向左/右选中一词
SelectToDocumentStart,SelectToDocumentEnd: 选中到篇头/篇尾
SelectToLineStart/SelectToLineEnd:选中到行首/行尾
ToggleBold, ToggleItalic, ToggleUnderline(加粗，斜体，下划线)
ToggleBullets, ToggleNumbering(列表：加点，加数字)
ToggleInsert:插入
ToggleSuperscript,ToggleSubscript(上标字，下标字)

六、命令参数

命令大部分都是类的静态属性，也就是示例只有一个，那么如果两个按钮使用同一个命令如何区分呢？比如新建一个Project,如何区分新建的是Library还是WPF呢？我们可以使用CommandParameter

XAML:

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<Window x:Class="DeepXAML.MainWindow"

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        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"

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        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"

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        xmlns:local="clr-namespace:DeepXAML"       

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        xmlns:sys="clr-namespace:System;assembly=mscorlib"

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        Title="MainWindow" Height="250" Width="450"> 

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    <Window.CommandBindings> 

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        <CommandBinding Command="New" CanExecute="New_CanExecute" Executed="New_Executed"></CommandBinding> 

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    </Window.CommandBindings> 

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        <StackPanel x:Name="stackPanel">         

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        <TextBox x:Name="textBox" Margin="10"></TextBox> 

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        <Button x:Name="btnWPF" Margin="10" Command="New" CommandParameter="WPF">新建WPF</Button> 

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        <Button x:Name="btnLibrary" Margin="10" Command="New" CommandParameter="Library">新建Library</Button> 

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    </StackPanel> 

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</Window>

后台代码：

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using System; 

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using System.Collections.Generic; 

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using System.Windows; 

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using System.Windows.Data; 

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using System.Windows.Documents; 

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using System.Windows.Controls; 

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using System.Windows.Input; 

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namespace DeepXAML 

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{ 

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    public partial class MainWindow : Window 

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    { 

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        public MainWindow() 

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        { 

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            InitializeComponent(); 

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        } 

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        private void New_CanExecute(object sender, CanExecuteRoutedEventArgs e) 

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        { 

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            e.CanExecute = string.IsNullOrEmpty(textBox.Text); 

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        } 

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        private void New_Executed(object sender, ExecutedRoutedEventArgs e) 

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        { 

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            if (e.Parameter.ToString() == "Library") 

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            { 

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                this.textBox.Text+= "建一个Library"; 

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            } 

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            if (e.Parameter.ToString() == "WPF") 

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            { 

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                this.textBox.Text += "建一个WPF"; 

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            }             

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        } 

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    }            

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}

运行：

点击第一个按钮

清空文本框再点击第二个按钮