为什么 ContextMenu Command 和 CommandParameter 在 DataGrid 中不起作用

Question

我有一个DataGird，然后它包括Expander 和ContextMenu。

这个DataGird 正在分组。而且，Expander 和 DataGridItem 之间的 ContextMenu 是不同的。

但是，我想将MenuItem Command 绑定到我的命令，并将DataGird 的SelectedItems 或SelectedIndex 传递给Command。

但是这个命令没有被调用。即使它有效，当我调查某些方法得到目标时，参数也不会通过（比如设置属性tag）。

所以，我想知道什么是正确的方法。

常规

<UserControl.DataContext>
    <vm:ViewModel x:Name="VM"/>
</UserControl.DataContext>
<Grid>
    <DataGrid x:Name="dg"
              ItemsSource="{Binding SourceData}"
              AutoGenerateColumns="False" 
              CanUserResizeColumns="False" 
              CanUserResizeRows="False"
              CanUserAddRows="False" 
              CanUserSortColumns="False"
              SelectionMode="Extended"
              RowHeaderWidth="0"
              GridLinesVisibility="Horizontal">
        <DataGrid.CellStyle>
            <Style TargetType="DataGridCell">
                <Setter Property="BorderThickness" Value="0"/>
                <!-- Remove the focus indication for the selected cell -->
                <Setter Property="FocusVisualStyle" Value="{x:Null}"/>
            </Style>
        </DataGrid.CellStyle>
        <DataGrid.Columns>
            <DataGridTextColumn Header="No." Binding="{Binding No}" />
            <DataGridTextColumn Header="Name" Binding="{Binding Name}"/>
        </DataGrid.Columns>
        <DataGrid.GroupStyle>
            <GroupStyle>
                <GroupStyle.ContainerStyle>
                    <Style TargetType="{x:Type GroupItem}">
                        <Setter Property="Template">
                            <Setter.Value>
                                <ControlTemplate>
                                    <Expander IsExpanded="False"  MouseRightButtonDown="Expander_MouseRightButtonDown" ButtonBase.Click="Expander_Click">
                                        <Expander.Header>
                                            <StackPanel Orientation="Horizontal">
                                                <StackPanel.ContextMenu>
                                                    <ContextMenu>
                                                        <MenuItem Header="Insert" InputGestureText="Ctrl+I" Command="{Binding InsertGroupItems"/>
                                                        <MenuItem Header="Remove" InputGestureText="Ctrl+D" Command="{Binding RemoveGroupItems"/>
                                                    </ContextMenu>
                                                </StackPanel.ContextMenu>
                                                <TextBlock Text="{Binding Name}"/>
                                                <TextBlock Text="{Binding ItemCount}"/>
                                                <TextBlock Text=" item(s)"/>
                                            </StackPanel>
                                        </Expander.Header>
                                        <ItemsPresenter>
                                            <ItemsPresenter.ContextMenu>
                                                <ContextMenu>
                                                    <ContextMenu>
                                                        <MenuItem Header="Insert" InputGestureText="Ctrl+I" Command="{Binding InsertSelectedItems" CommandParameter="{Binding ElementName=dg, Path=SelectedIndex}"/>
                                                        <MenuItem Header="Remove" InputGestureText="Ctrl+D" Command="{Binding RemoveSelectedItems" CommandParameter="{Binding ElementName=dg, Path=SelectedItems}"/>
                                                    </ContextMenu>
                                            </ItemsPresenter.ContextMenu>
                                        </ItemsPresenter>
                                    </Expander>
                                </ControlTemplate>
                            </Setter.Value>
                        </Setter>
                    </Style>
                </GroupStyle.ContainerStyle>
            </GroupStyle>
        </DataGrid.GroupStyle>
    </DataGrid>
</Grid>

这个工作调用命令，但是不能传参数

<DataGrid.GroupStyle>
            <GroupStyle>
                <GroupStyle.ContainerStyle>
                    <Style TargetType="{x:Type GroupItem}">
                        <Style TargetType="{x:Type GroupItem}">
                            <Setter Property="Tag" Value="{Binding DataContext, RelativeSource={RelativeSource AncestorType=DataGrid}}" />
                            <Setter Property="ContextMenu">
                                <Setter.Value>
                                    <ContextMenu>
                                        <MenuItem Header="Insert" InputGestureText="Ctrl+I" Command="{Binding PlacementTarget.Tag.InsertSelectedItems, RelativeSource={RelativeSource AncestorType=ContextMenu}}" CommandParameter="{Binding ElementName=dg, Path=SelectedIndex}"/>
                                        <MenuItem Header="Remove" InputGestureText="Ctrl+D" Command="{Binding PlacementTarget.Tag.RemoveSelectedItems, RelativeSource={RelativeSource AncestorType=ContextMenu}}" CommandParameter="{Binding ElementName=dg, Path=SelectedItems}"/>
                                    </ContextMenu>
                                </Setter.Value>
                            </Setter>
                            <Setter Property="Template">
                                <Setter.Value>
                                    <ControlTemplate>
                                        <Expander IsExpanded="False"  MouseRightButtonDown="Expander_MouseRightButtonDown" ButtonBase.Click="Expander_Click">
                                            <Expander.Header>
                                                <StackPanel Orientation="Horizontal">
                                                    <StackPanel.ContextMenu>
                                                        <ContextMenu>
                                                            <MenuItem Header="Insert" InputGestureText="Ctrl+I" Command="{Binding InsertGroupItems}"/>
                                                            <MenuItem Header="Remove" InputGestureText="Ctrl+D" Command="{Binding RemoveGroupItems}"/>
                                                        </ContextMenu>
                                                    </StackPanel.ContextMenu>
                                                    <TextBlock Text="{Binding Name}"/>
                                                    <TextBlock Text="{Binding ItemCount}"/>
                                                    <TextBlock Text=" item(s)"/>
                                                </StackPanel>
                                            </Expander.Header>
                                            <ItemsPresenter/>
                                        </Expander>
                                    </ControlTemplate>
                                </Setter.Value>
                            </Setter>
                    </Style>
                </GroupStyle.ContainerStyle>
            </GroupStyle>
        </DataGrid.GroupStyle>

顺便说一句，SelectedItems 获取参数时如何转换？

不行

private void Excute(object parameter)
{
    IList list = parameter as IList;
    foreach (var item in list)
    {
        Remove((Data)item);
    }
}

所以，也许我有三个问题。

1. ContextMenu 不起作用。

2. CommandParameter 没有通过。

3. 如何将SelectedItems转换为列表？

谢谢！

Answer 1

ContextMenu 中的MenuItem 不能使用ElementName 绑定到DataGrid，因为ContextMenu 和DataGrid 属于不同的元素树。

您可以做的是将ItemsPresenter的Tag属性绑定到DataGrid，然后通过ContextMenu的PlacementTarget绑定到DataGrid的属性：

<ItemsPresenter Tag="{Binding RelativeSource={RelativeSource AncestorType=DataGrid}}">
    <ItemsPresenter.ContextMenu>
        <ContextMenu>
            <MenuItem Header="Insert2" InputGestureText="Ctrl+I"
                        DataContext="{Binding PlacementTarget.Tag, RelativeSource={RelativeSource AncestorType=ContextMenu}}"
                        Command="{Binding DataContext.InsertSelectedItems}"
                        CommandParameter="{Binding SelectedIndex}"/>
            <MenuItem Header="Remove2" InputGestureText="Ctrl+D"
                        DataContext="{Binding PlacementTarget.Tag, RelativeSource={RelativeSource AncestorType=ContextMenu}}"
                        Command="{Binding DataContext.RemoveSelectedItems}"
                        CommandParameter="{Binding SelectedItems}"/>
        </ContextMenu>
    </ItemsPresenter.ContextMenu>
</ItemsPresenter>

如何将 SelectedItems 转换为列表？

就像你正在做的那样。如果绑定到DataGrid 的SelectedItems 属性有效，这应该可以工作：

private void Execute(object parameter)
{
    IList list = parameter as IList;
    foreach (var item in list)
    {
        Remove((Data)item);
    }
}

编辑：

当然，在绑定到CommandArgument 时也不能使用ElementName。试试这个：

<Style TargetType="{x:Type GroupItem}">
    <Setter Property="Tag" Value="{Binding Path=., RelativeSource={RelativeSource AncestorType=DataGrid}}" />
    <Setter Property="ContextMenu">
        <Setter.Value>
            <ContextMenu>
                <MenuItem Header="Insert" InputGestureText="Ctrl+I"
                          Command="{Binding PlacementTarget.Tag.DataContext.InsertSelectedItems, RelativeSource={RelativeSource AncestorType=ContextMenu}}"
                          CommandParameter="{Binding PlacementTarget.Tag.SelectedIndex, RelativeSource={RelativeSource AncestorType=ContextMenu}}"/>
                <MenuItem Header="Remove" InputGestureText="Ctrl+D"
                          Command="{Binding PlacementTarget.Tag.DataContext.RemoveSelectedItems, RelativeSource={RelativeSource AncestorType=ContextMenu}}"
                          CommandParameter="{Binding PlacementTarget.Tag.SelectedItems, RelativeSource={RelativeSource AncestorType=ContextMenu}}"/>
            </ContextMenu>
        </Setter.Value>
    </Setter>