WPF MenuItem.Command绑定到ElementName结果到System.Windows.Data错误：4：找不到与引用绑定的源 [英] WPF MenuItem.Command binding to ElementName results to System.Windows.Data Error: 4 : Cannot find source for binding with reference

问题描述

我有以下XAML：

<UserControl x:Class="EMS.Controls.Dictionary.TOCControl"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:vm="clr-namespace:EMS.Controls.Dictionary.Models"
    xmlns:diagnostics="clr-namespace:System.Diagnostics;assembly=WindowsBase"
    x:Name="root"  >

    <TreeView                    
        x:Name="TOCTreeView"                    
        Background="White"
         Padding="3,5"      
        ContextMenuOpening="TOCTreeView_ContextMenuOpening"
        ItemsSource="{Binding Children}" BorderBrush="{x:Null}"  >

        <TreeView.ItemTemplate>
            <HierarchicalDataTemplate ItemsSource="{Binding Path=Children, Mode=OneTime}">
                <Grid >
                    <Grid.ColumnDefinitions>
                        <ColumnDefinition Width="Auto"/>
                        <!--<ColumnDefinition Width="Auto"/>-->                       
                        <ColumnDefinition Width="*"/>
                    </Grid.ColumnDefinitions>
                    <!--<CheckBox VerticalAlignment="Center" IsChecked="{Binding IsVisible}"/>-->   
                    <ContentPresenter Grid.Column="0" Height="16" Width="20"
                                    Content="{Binding LayerRepresentation}"  />
                    <!--<ContentPresenter Grid.Column="1"      >
                        <ContentPresenter.Content>
                            Test
                        </ContentPresenter.Content>
                    </ContentPresenter>-->
                    <TextBlock Grid.Column="2" FontWeight="Normal" Text="{Binding Path=Alias, Mode=OneWay}" >
                        <ToolTipService.ToolTip>
                            <TextBlock Text="{Binding Description}" TextWrapping="Wrap"/>
                        </ToolTipService.ToolTip>
                    </TextBlock>
                </Grid>
                <HierarchicalDataTemplate.ItemTemplate>
                    <HierarchicalDataTemplate ItemsSource="{Binding Path=Children, Mode=OneTime}">
                        <!--<DataTemplate>-->
                        <Grid >
                            <Grid.ColumnDefinitions>
                                <ColumnDefinition Width="Auto"/>
                                <ColumnDefinition Width="Auto"/>                               
                                <ColumnDefinition Width="*"/>
                            </Grid.ColumnDefinitions>
                            <CheckBox VerticalAlignment="Center" IsChecked="{Binding IsVisible}"/>
                            <ContentPresenter Grid.Column="1"
                                    Content="{Binding LayerRepresentation, Mode=OneWay}"  />
                            <TextBlock Margin="0,1,0,1" Text="{Binding Path=Alias, Mode=OneWay}" Grid.Column="2">
                                <ToolTipService.ToolTip>
                                    <TextBlock Text="{Binding Description}" TextWrapping="Wrap"/>
                                </ToolTipService.ToolTip>                   
                            </TextBlock>
                        </Grid>
                        <!--</DataTemplate>-->
                    </HierarchicalDataTemplate>                  
                </HierarchicalDataTemplate.ItemTemplate>
            </HierarchicalDataTemplate>
        </TreeView.ItemTemplate> 

        <TreeView.ContextMenu>
            <ContextMenu>
                <MenuItem Name="miRemove" Header="Remove"
                          Command="{Binding ElementName=root, Path=RemoveItemCmd, 
                    diagnostics:PresentationTraceSources.TraceLevel=High}">
                    <MenuItem.Icon>
                        <Image Source="../images/16x16/Delete.png"/>
                    </MenuItem.Icon>
                </MenuItem>
                <MenuItem Header="Properties"
                          Command="{Binding ElementName=root, Path=GetItemPropertiesCmd}"/>               
            </ContextMenu>       
        </TreeView.ContextMenu>


    </TreeView>

</UserControl>

此UserControl的代码背后有两个ICommand属性，名称为：RemoveItemCmd和GetItemPropertiesCmd。但是，我得到

Code behind for this UserControl has two ICommand properties with names: RemoveItemCmd and GetItemPropertiesCmd. However, I get

System.Windows.Data Error: 4 : Cannot find source for binding with reference 'ElementName=root'. BindingExpression:Path=RemoveItemCmd; DataItem=null; target element is 'MenuItem' (Name='miRemove'); target property is 'Command' (type 'ICommand')
System.Windows.Data Error: 4 : Cannot find source for binding with reference 'ElementName=root'. BindingExpression:Path=GetItemPropertiesCmd; DataItem=null; target element is 'MenuItem' (Name=''); target property is 'Command' (type 'ICommand')

为什么是这样的，我该如何解决？

when UserControl is constructed. Why is this and how do I resolve?

推荐答案

您无法使用上下文菜单中的元素名称进行绑定。链接在上下文菜单及其放置目标之间被断开。您可以使用几个技巧来解决它。

You can't bind using element name from a context menu. The link is broken between the context menu and its placement target. You can get around it using a couple of tricks though...

1. 使用RoutedUICommands在UserControl上绑定命令，然后没有绑定



2. 在上下文菜单的DataContext中使用放置目标绑定。这允许您至少获取上下文菜单显示在上下文菜单上的元素的数据上下文。

1. Use RoutedUICommands with a command binding on the UserControl, then no binding is needed.

2. Use the placement target binding on the context menu's DataContext. This allows you to at least get the data context of the element the context menu appears on to the context menu.

DataContext ={Binding RelativeSource = {RelativeSource Mode = Self }，Path = PlacementTarget.DataContext}

DataContext="{Binding RelativeSource={RelativeSource Mode=Self}, Path=PlacementTarget.DataContext}"

（我认为这是你想要的）您可以访问静态资源 ElementSpy 允许您使用静态资源链接到窗口，以便您可以然后使用一个defacto ElementName绑定。

(and i think this is what you want) You can access a static resource, ElementSpy lets you link to the window using a static resource so you can then use a defacto ElementName bindings.

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