Binding-Error with ComboBoxItem in DataGrid

Question

I have a UserControl with a DataGrid in it. The columns of the DataGrid do I create as DataGridTemplateColumns. The DataGrid looks something like:

<DataGrid Grid.Row="1" Style="{StaticResource DataGridStyle}" Margin="5"
      ItemsSource="{Binding Storage.Items, UpdateSourceTrigger=PropertyChanged}"
      SelectedItem="{Binding SelectedItem, Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}"
      MaxHeight="400" VerticalAlignment="Top">
      <DataGrid.Columns>
        <DataGridTemplateColumn Header="Comment" Width="*" SortMemberPath="Comment">
            <DataGridTemplateColumn.CellTemplate>
                <DataTemplate>
                    <TextBlock Text="{Binding Comment}" Margin="3,2" VerticalAlignment="Center"/>
                </DataTemplate>
            </DataGridTemplateColumn.CellTemplate>
        </DataGridTemplateColumn>

        // several more column-definitions                      

        <DataGridTemplateColumn Header="Actions" Width="90">
            <DataGridTemplateColumn.CellTemplate>
                <DataTemplate>
                    <Button Margin="5" Content="Action..." Cursor="Hand" >
                        <Button.Template>
                            <ControlTemplate TargetType="{x:Type Button}">
                                <TextBlock TextDecorations="Underline" HorizontalAlignment="Center" Foreground="Blue">
                                    <ContentPresenter/>
                                </TextBlock>
                            </ControlTemplate>
                        </Button.Template>
                        <Button.Style>
                            <Style TargetType="{x:Type Button}">
                                <Style.Triggers>
                                    <EventTrigger RoutedEvent="Click">
                                        <EventTrigger.Actions>
                                            <BeginStoryboard>
                                                <Storyboard>
                                                    <BooleanAnimationUsingKeyFrames Storyboard.TargetProperty="ContextMenu.IsOpen">
                                                        <DiscreteBooleanKeyFrame KeyTime="0:0:0" Value="True"/>
                                                    </BooleanAnimationUsingKeyFrames>
                                                </Storyboard>
                                            </BeginStoryboard>
                                        </EventTrigger.Actions>
                                    </EventTrigger>
                                </Style.Triggers>
                                <Setter Property="ContextMenu">
                                    <Setter.Value>
                                        <ContextMenu>                                                            
                                            <MenuItem Header="Edit"/>
                                            <MenuItem Header="Delete" Command="{Binding DataContext.CommonCommand, 
                                                RelativeSource={RelativeSource FindAncestor, AncestorType=UserControl}}" 
                                                      CommandParameter="{x:Static defs:CommonCommandTarget.Delete}"/>
                                            <Separator/>
                                        </ContextMenu>
                                    </Setter.Value>
                                </Setter>
                            </Style>
                        </Button.Style>
                    </Button>
                </DataTemplate>
            </DataGridTemplateColumn.CellTemplate>
        </DataGridTemplateColumn>+
    </DataGrid.Columns>
</DataGrid>

My problem is the binding of the Delete-Command of the ContextMenu in the last column. The contextmenu is shown but on a click nothing happens.

In the output I can see a binding-error:

System.Windows.Data Error: 4 : Cannot find source for binding with reference 'RelativeSource FindAncestor, AncestorType='System.Windows.Controls.DataGrid', AncestorLevel='1''. BindingExpression:Path=DataContext.CommonCommand; DataItem=null; target element is 'MenuItem' (Name=''); target property is 'Command' (type 'ICommand')

Outside the DataGrid or a Button directly in the Template-Column just works fine with the binding. so the Command is correctly.

What Ancestor or RelativeSource or whatever do I have to provide that my Command in the ViewModel will be called?

pangular pangular · Accepted Answer · 2015-03-05T15:30:14

You can only use the RelativeSource markup extension from within the scope of a Visual Tree. DataGridTemplateColumn is not a part of the Visual Tree. Check out this answer.

Binding-Error with ComboBoxItem in DataGrid

1 Answers