将上下文菜单绑定到视图模型属性

Question

我有一个上下文菜单,它绑定到数据网格中的按钮.我希望上下文菜单项根据我在视图模型中的字符串列表进行更改.当我单击按钮时,没有任何显示.

这是我正在使用的xaml,它位于datagrid中:

<Button Grid.Column="1" Content="..."  Click="Button_Click">
        <Button.ContextMenu>
       <ContextMenu ItemsSource="{Binding RelativeSource={RelativeSource Mode=FindAncestor,AncestorType={x:Type UserControl}},Path=DataContext.SelectableDescriptions}">    
         <TextBlock Text="{Binding}"/>
       </ContextMenu>
       </Button.ContextMenu>        
</Button>

这是整个DataGrid xaml:

<DataGrid Grid.Row="1" Grid.ColumnSpan="4" CanUserAddRows="True" AutoGenerateColumns="False" CanUserDeleteRows="True"  ItemsSource="{Binding JobPricings, Mode=TwoWay}" SelectedItem="{Binding SelectedJobPricing, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" >
    <DataGrid.Columns>
        <DataGridTemplateColumn  Header="Description" Width="25*"   >
            <DataGridTemplateColumn.CellTemplate>
                <DataTemplate>
                    <Grid>
                        <Grid.ColumnDefinitions>
                            <ColumnDefinition Width="75*"/>
                            <ColumnDefinition Width="25*"/>
                        </Grid.ColumnDefinitions>
                        <TextBox Grid.Column="0" Text="{Binding Description,Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"/>
                        <Button Grid.Column="1" Content="..."  Click="Button_Click">
                            <Button.ContextMenu>
                                <ContextMenu ItemsSource="{Binding RelativeSource={RelativeSource Mode=FindAncestor,AncestorType={x:Type UserControl}},Path=DataContext.SelectableDescriptions}">
                                    <TextBlock Text="{Binding}"/>
                                </ContextMenu>
                            </Button.ContextMenu>
                        </Button>
                    </Grid>
                </DataTemplate>
            </DataGridTemplateColumn.CellTemplate>
         </DataGridTemplateColumn>
        <DataGridTextColumn Header="Unit Price" Binding="{Binding UnitPrice, Mode=TwoWay}" Width="25*"/>
        <DataGridTextColumn Header="Unit" Binding="{Binding Unit, Mode=TwoWay}" Width="25*"/>
        <DataGridTemplateColumn  Header="Currency   " Width="25*" >
            <DataGridTemplateColumn.CellTemplate>
                <DataTemplate>
                    <Grid>
                        <ComboBox  SelectedValue="{Binding CurrencyID, Mode=TwoWay}" SelectedValuePath="ID" DisplayMemberPath="Description" ItemsSource="{Binding RelativeSource={RelativeSource Mode=FindAncestor,AncestorType={x:Type UserControl}},Path=DataContext.Currencies}"  ></ComboBox>
                    </Grid>
                </DataTemplate>
            </DataGridTemplateColumn.CellTemplate>
        </DataGridTemplateColumn>
    </DataGrid.Columns>
</DataGrid>

这是我通过我的视图模型绑定上下文菜单的属性:

public ObservableCollection<string> SelectableDescriptions
{
    get
    {
        _selectableDescriptions.Add("One");
        _selectableDescriptions.Add("Two");
        return _selectableDescriptions;
    }
    set
    {
        _selectableDescriptions = value;
    }
}

我的列表为什么不会出现在上下文菜单中的任何想法？

Answer 1

正如约翰所说,ContextMenu它是独立的窗口,与按钮的可视树分开,因此它不会自动继承按钮DataContext.

然而,一个ContextMenu确实有一个链接到它被放置在(你的情况的按钮)对象:PlacementTarget.通过转到菜单的PlacementTarget,您可以找到该按钮,当您找到该按钮时,您可以找到它的DataContext.

因此,在xaml中,您可以通过将自己PlacementTarget.DataContext的DataContext 绑定到自己的DataContext来手动使ContextMenu继承Button的DataContext ,并且所有其他绑定(例如for ItemsSource)可以像普通的一样编写:

<Button Grid.Column="1" Content="..."  Click="Button_Click">
    <Button.ContextMenu>
        <ContextMenu DataContext="{Binding RelativeSource={RelativeSource Self}, Path=PlacementTarget.DataContext}" 
                     ItemsSource="{Binding Path=SelectableDescriptions}" >    
            <ContextMenu.ItemTemplate>
                <DataTemplate>
                    <TextBlock Text="{Binding Path=SomePropertyOnItem}" />
                </DataTemplate>
            </ContextMenu.ItemTemplate>                            
        </ContextMenu>
    </Button.ContextMenu>        
</Button>