如何在ContextMenu上啟用選單項-WPF-有解無憂

我正在嘗試在 UserControl 派生物件上創建 ContextMenu。注意：這不是 WinForms 應用程式，它是純 WPF。

所以我創建了 ContextMenu ：

    <UserControl.Resources>
        <ContextMenu x:Key="cmLCD_CopyCutPaste">
            <MenuItem Name="CutOption"  Header="{x:Static p:Resources.Popup_Cut}" Command="Cut" Click="MenuItem_Cut" IsEnabled="True"/>
            <MenuItem Name="CopyOption" Header="{x:Static p:Resources.Popup_Copy}" Command="Copy" Click="MenuItem_Copy" IsEnabled="True"/>
            <MenuItem Name="PasteOption" Header="{x:Static p:Resources.Popup_Paste}" Command="Paste" Click="MenuItem_Paste" IsEnabled="True"/>
        </ContextMenu>
    </UserControl.Resources>

滑鼠按鈕事件是這樣設定的：

d:DesignHeight="66" d:DesignWidth="340" Focusable="True" KeyDown="Grid_KeyDown" MouseRightButtonDown="EMS_UI_LCDscreen_MouseRightButtonDown" >

在后面的代碼中，建構式是這樣開始的：

        public EMS_UI_LCDscreen()
        {
            InitializeComponent();

            // Find the ContextMenu created on this object - it is called cmLCD_CopyCutPaste
            ContextMenu cm = FindResource("cmLCD_CopyCutPaste") as ContextMenu;

            // If we found the contextMenu, assign it the ContextMenu placeholder for this instance.
            if (cm != null)
            {
                ContextMenu = cm;
            }

            ...

滑鼠單擊（右鍵）的處理方式如下：

        private void EMS_UI_LCDscreen_MouseRightButtonDown(object sender, MouseButtonEventArgs e)
        {
            if (this.ContextMenu is ContextMenu cm)
            {
                if (cm != null)
                {
                    if (DataContext is DeviceEditorData ded)
                    {
                        cm.DataContext = ded.Device.GetStructuredLocation(0);

                        cm.IsEnabled = true;

                        cm.PlacementTarget = sender as Button;
                        cm.IsOpen = true;
                    }
                }
            }
        }

有三個事件處理程式來實際回應 ContextMenu 上的用戶選擇：

        private void MenuItem_Cut(object sender, RoutedEventArgs e)
        {
        }

        private void MenuItem_Copy(object sender, RoutedEventArgs e)
        {
        }

        private void MenuItem_Paste(object sender, RoutedEventArgs e)
        {
        }

LCD 影像組件上顯示的 ContextMenu 視圖

The component I have created appears in a few different contexts, but the one I'm mainly interested in is inside of a DataGrid that shows various items of data, each with one of these components. when right clicked, the component faithfully displays the popup context menu as expected..... BUT all the items on the menu are grayed out and basically not enabled. So my question is, what is the missing piece of glue that effectively enables the menu items so that they can be clicked to do the required actions. Most of the answers already seen on the net go into detail of how to do it in a WinForms app, but despite hours of searching, I can find no clear solution to what should be a very simple task of enabling the menu items. Can some kind soul please put me out of my anguish and in a few lines of code show me how to do it! Thank you

UPDATE: This is the XAML implementation for the LCD Component:

<UserControl x:Class="EMS_Config_Tool.UIComponents.WPF.EMS_UI_LCDscreen"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
             xmlns:p="clr-namespace:EMS_Config_Tool.Properties"
             mc:Ignorable="d" 
             d:DesignHeight="66" d:DesignWidth="340" Focusable="True" KeyDown="Grid_KeyDown" MouseRightButtonDown="EMS_UI_LCDscreen_MouseRightButtonDown" >

    <UserControl.Resources>
        <ContextMenu x:Key="cmLCD_CopyCutPaste">
            <MenuItem Name="CutOption"  Header="{x:Static p:Resources.Popup_Cut}" Command="{Binding Cut}"/>
            <MenuItem Name="CopyOption" Header="{x:Static p:Resources.Popup_Copy}" Command="{Binding Copy}"/>
            <MenuItem Name="PasteOption" Header="{x:Static p:Resources.Popup_Paste}" Command="{Binding Paste}"/>
        </ContextMenu>
    </UserControl.Resources>

    <UserControl.CommandBindings>
        <CommandBinding Command="Cut"
                        CanExecute="CutCommand_CanExecute"
                        Executed="CutCommand_Executed" />

        <CommandBinding Command="Copy"
                        CanExecute="CopyCommand_CanExecute"
                        Executed="CopyCommand_Executed" />
        
        <CommandBinding Command="Paste"
                        CanExecute="PasteCommand_CanExecute"
                        Executed="PasteCommand_Executed" />
    </UserControl.CommandBindings>

</UserControl>

As can be seen, it is very simple - there are no items added to the control - it only serves as a Canvas upon which the code behind draws all the needed items which are purely graphic "draw" items.

This is the implementations of the 6 methods referenced, in the corresponding .cs file for the xaml above:

        private void CutCommand_CanExecute(object sender, CanExecuteRoutedEventArgs e)
        {
            // Verify relevant conditions and set CanExecuteRoutedEventArgs.CanExecute accordingly
            e.CanExecute = true;
        }
        private void CutCommand_Executed(object sender, ExecutedRoutedEventArgs e)
        {
            // Execute the command action
            if (sender is EMS_UI_LCDscreen lcd)
            {
                if (TheDevice != null)
                {
                    Clipboard.SetDataObject(TheDevice.GetStructuredLocation(0).ToString());

                    TheDevice.SetLocation(0, "");

                    lcd.StructuredTextToShow = TheDevice.GetStructuredLocation(0);
                }
                else
                {
                    Clipboard.SetDataObject(lcd.StructuredTextToShow.ToString());

                    lcd.StructuredTextToShow.SetString("");
                }
            }
        }
        private void CopyCommand_CanExecute(object sender, CanExecuteRoutedEventArgs e)
        {
            // Verify relevant conditions and set CanExecuteRoutedEventArgs.CanExecute accordingly
            e.CanExecute = true;
        }
        private void CopyCommand_Executed(object sender, ExecutedRoutedEventArgs e)
        {
            // Execute the command action
            if (sender is EMS_UI_LCDscreen lcd)
            {
                if (TheDevice!=null)
                    Clipboard.SetDataObject(TheDevice.GetStructuredLocation(0).ToString());
                else
                    Clipboard.SetDataObject(lcd.StructuredTextToShow.ToString());
            }
        }
        private void PasteCommand_CanExecute(object sender, CanExecuteRoutedEventArgs e)
        {
            // Verify relevant conditions and set CanExecuteRoutedEventArgs.CanExecute accordingly
            IDataObject iData = Clipboard.GetDataObject();

            // Is the Data Text?  
            if (iData.GetDataPresent(DataFormats.Text))
                e.CanExecute = true;
            else
                e.CanExecute = false;
        }
        private void PasteCommand_Executed(object sender, ExecutedRoutedEventArgs e)
        {
            // Execute the command action
            if (sender is EMS_UI_LCDscreen lcd)
            {
                // Retrieves data  
                IDataObject iData = Clipboard.GetDataObject();

                // Is the Data Text?  
                if (iData.GetDataPresent(DataFormats.Text))
                {
                    if (TheDevice != null)
                    {
                        TheDevice.SetLocation(0, (string)iData.GetData(DataFormats.Text));

                        lcd.StructuredTextToShow = TheDevice.GetStructuredLocation(0);
                    }
                    else
                    {
                        lcd.StructuredTextToShow.SetString((string)iData.GetData(DataFormats.Text));
                    }
                }
            }
        }

Finally, the ContextMenu is assigned to the object in the constructor:

        public EMS_UI_LCDscreen()
        {
            InitializeComponent();

            // Find the ContextMenu created on this object - it is called cmLCD_CopyCutPaste
            ContextMenu cm = FindResource("cmLCD_CopyCutPaste") as ContextMenu;

            // If we found the contextMenu, assign it the ContextMenu placeholder for this instance.
            if (cm != null)
            {
                ContextMenu = cm;
            }

            ...

The menu is shown on the component in response to right-click, the cut/copy/paste methods respond to the key ops, but clicking on the menu items does not fire the corresponding methods. I can't see why that should be so, it all looks correct to me, but perhaps there is something missing that is preventing it working. One suggestion was to use a "relay command" type of thingy, but what and how that may be, is unclear.

uj5u.com熱心網友回復：

您應該洗掉所有設定IsEnabled為true. 它是多余的，因為該值是true默認值。

這些按鈕被禁用是因為您（不小心？）將命令附加到MenuItem.Command屬性但沒有相應的命令處理程式。
框架將嘗試呼叫CanExecute處理程式。由于沒有定義，因此回傳一個默認處理程式，設定CanExecuteRoutedEventArgs.CanExecute為false，這將禁用按鈕 ( ICommandSource)。

不確定您是否打算在這里使用命令，或者您錯誤地猜測該Command屬性就像一個名稱屬性（因為您還注冊了Click事件處理程式）。請參閱指揮概述了解更多資訊。

無論如何，這是注冊命令處理程式的方法：

您已分配預定義的應用程式命令（剪切、復制和粘貼 - MenuItem.CommandXAML 中的字串值隱式參考靜態ApplicationCommands命令）。這些命令是路由命令（行為與路由事件相同 - 實際上路由命令是路由事件）。因此，您必須在命令源的父元素（呼叫命令的元素）上定義命令系結，因為命令會在樹中冒泡。

AUIElement.CommandBinding由指定的CommandBinding.Executed處理程式和可選 CommandBinding.CanExecute的處理程式組成。
使用CanExecute處理程式來控制命令源的禁用狀態，例如Button. 如果應該始終啟用命令源，只需省略CanExecute處理程式。

XAML

<Window>
  <Window.CommandBindings>
    <CommandBinding Command="Cut"
                    CanExecute="CutCommand_CanExecute"
                    Executed="CutCommand_Executed" />
  </Window.CommandBindings>
</Window>

C＃

partial class MainWindow : Window
{
  public MainWindow()
  {
    InitializeComponent();

    var cutCommandBinding = 
      new CommandBinding(ApplicationCommands.Cut, CutCommand_Executed, CutCommand_CanExecute)
    this.CommandBindings.Add(cutCommandBinding);
  }
}

然后在代碼隱藏中創建相應的命令處理程式。

private void CutCommand_CanExecute(object sender, CanExecuteRoutedEventArgs e)
{
  // Verify relevant conditions and set CanExecuteRoutedEventArgs.CanExecute accordingly
  e.CanExecute = true;
}

private void CutCommand_Executed(object sender, ExecutedRoutedEventArgs e)
{
  // Execute the command action
}

更新

要強制對進行命令處理UserControl，您可以顯式設定MenuItem.CommandTarget屬性以參考UserControl.
您還可以UserControl.Contextmenu從 XAML分配：

<UserControl>
    <UserControl.Resources>
        <Style TargetType="MenuItem">
            <Setter Property="CommandTarget"
                    Value="{Binding RelativeSource={RelativeSource AncestorType={x:Type ContextMenu}}, Path=PlacementTarget}" />
        </Style>
    </UserControl.Resources>

    <UserControl.Contextmenu>
        <ContextMenu>
            <MenuItem Name="CutOption"  Header="{x:Static p:Resources.Popup_Cut}" Command="{Binding Cut}"/>
            <MenuItem Name="CopyOption" Header="{x:Static p:Resources.Popup_Copy}" Command="{Binding Copy}"/>
            <MenuItem Name="PasteOption" Header="{x:Static p:Resources.Popup_Paste}" Command="{Binding Paste}"/>
        </ContextMenu>
    </UserControl.Contextmenu>

    <UserControl.CommandBindings>
        <CommandBinding Command="Cut"
                        CanExecute="CutCommand_CanExecute"
                        Executed="CutCommand_Executed" />

        <CommandBinding Command="Copy"
                        CanExecute="CopyCommand_CanExecute"
                        Executed="CopyCommand_Executed" />
        
        <CommandBinding Command="Paste"
                        CanExecute="PasteCommand_CanExecute"
                        Executed="PasteCommand_Executed" />
    </UserControl.CommandBindings>
</UserControl>

uj5u.com熱心網友回復：

這是最終對我有用的解決方案。長生不老藥是在分配命令，而不是使用“系結”術語，而是直接：

<UserControl x:Class="EMS_Config_Tool.UIComponents.WPF.EMS_UI_LCDscreen"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
             xmlns:p="clr-namespace:EMS_Config_Tool.Properties"
             mc:Ignorable="d" 
             d:DesignHeight="66" d:DesignWidth="340" Focusable="True" KeyDown="Grid_KeyDown" MouseRightButtonDown="EMS_UI_LCDscreen_MouseRightButtonDown" >

    <UserControl.Resources>
        <Style TargetType="MenuItem">
            <Setter Property="CommandTarget"
                    Value="{Binding RelativeSource={RelativeSource AncestorType={x:Type ContextMenu}}, Path=PlacementTarget}" />
        </Style>
    </UserControl.Resources>

    <UserControl.ContextMenu>
        <ContextMenu>
            <MenuItem Name="CutOption"  Header="{x:Static p:Resources.Popup_Cut}" Command="Cut" />
            <MenuItem Name="CopyOption" Header="{x:Static p:Resources.Popup_Copy}" Command="Copy" />
            <MenuItem Name="PasteOption" Header="{x:Static p:Resources.Popup_Paste}" Command="Paste" />
        </ContextMenu>
    </UserControl.ContextMenu>

    <UserControl.CommandBindings>
        <CommandBinding Command="Cut"
                        CanExecute="CutCommand_CanExecute"
                        Executed="CutCommand_Executed" />

        <CommandBinding Command="Copy"
                        CanExecute="CopyCommand_CanExecute"
                        Executed="CopyCommand_Executed" />

        <CommandBinding Command="Paste"
                        CanExecute="PasteCommand_CanExecute"
                        Executed="PasteCommand_Executed" />
    </UserControl.CommandBindings>

</UserControl>

影像的建構式和賦值如下所示：

        public EMS_UI_LCDscreen()
        {
            InitializeComponent();

            Image ObjImage1 = new Image();
            Image ObjImage2 = new Image();
            Image ObjImage3 = new Image();

            ObjImage1.Source = new BitmapImage(new Uri(@"pack://application:,,,/Graphics\Misc Icons\Cut.png"));
            CutOption.Icon   = ObjImage1;

            ObjImage2.Source = new BitmapImage(new Uri(@"pack://application:,,,/Graphics\Misc Icons\Copy.png"));
            CopyOption.Icon  = ObjImage2;

            ObjImage3.Source = new BitmapImage(new Uri(@"pack://application:,,,/Graphics\Misc Icons\Paste.png"));
            PasteOption.Icon = ObjImage3;

            ...

...并在組件上顯示背景關系選單以回應滑鼠右鍵單擊：

        private void EMS_UI_LCDscreen_MouseRightButtonDown(object sender, MouseButtonEventArgs e)
        {
            if (ContextMenu is ContextMenu cm)
            {
                if (DataContext is DeviceEditorData ded)
                {
                    cm.DataContext = ded.Device.GetStructuredLocation((uint)LocationIndex);

                    cm.IsEnabled = true;

                    cm.PlacementTarget = sender as EMS_UI_LCDscreen;
                    cm.IsOpen = true;
                }
                if (DataContext is EMSBasicDevice dev)
                {
                    cm.DataContext = dev.GetStructuredLocation((uint)LocationIndex);

                    cm.IsEnabled = true;

                    cm.PlacementTarget = sender as EMS_UI_LCDscreen;
                    cm.IsOpen = true;
                }
            }
        }

為簡潔起見，我沒有顯示 ..._CanExecute / ...Executed 方法，它們如前面問題中所示。

感謝所有幫助解決此問題的人。

原位完成的背景關系選單的視圖

uj5u.com熱心網友回復：

因此，如果您使用DataContextand Binding，您可以執行以下操作

洗掉帶有事件處理程式的直接控制，即Click，并直接設定Enabled.
用于Binding將選單操作系結到視圖模型內的處理程式：（Command={Binding CutCommand}或任何其他處理程式）。
使用ICommand.CanExecute命令處理程式（CutCommand在上面的示例中）。管理Enabled選單項的狀態。

所以，讓我們把所有東西放在一起。

在 XAML 中

<MenuItem Name="CutOption"  Header="{x:Static p:Resources.Popup_Cut}" 
    Command="{Binding CutCommand}"/>

在視圖模型中

class ViewModel: INotifyPropertyChanged
{
    ...
    public ICommand CutCommand { get; }

    public ViewModel()
    {
        //you can just omit second arg if you always can call Cut.
        CutCommand = new RelayCommand(CutHandler, ()=>CanCut())); 
    }
    ...
}

這RelayCommand是https://docs.microsoft.com/en-us/windows/communitytoolkit/mvvm/relaycommand或任何其他簡單命令的實作。

如果您需要Enabled即時更新狀態，您可以呼叫CommandManager.InvalidateRequerySuggested();以重新評估CanExecute所有命令。

轉載請註明出處，本文鏈接：https://www.uj5u.com/gongcheng/419054.html

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