如何从DataGridColumn绑定到MVVM中的WPF DataGridColumn？

Question

我有一个包含不同列的DataGrid (TextBox、Combobox、DataPicker等)。通过MVVM显示数据。现在，我希望通过所选列对每个ContextMenu进行ColumnHeader到Group，但无法访问该列的绑定源(绑定路径)来告诉ViewModell它必须分组哪一列。当我第一次打开上下文菜单时，它工作得很好，但是当我再次打开上下文菜单时，它仍然从第一次开始传递SortMemberPath。我做错了什么？

XAML：

<DataGrid.Resources>
    <ContextMenu x:Key="DataGridColumnHeaderMenu">
        <MenuItem Name="mi_group" Header="Grouping"                                             
                  Command="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type local:MainWindow}}, Path=DataContext.GroupColumn}"
                  CommandParameter="{Binding Path=Column.SortMemberPath, RelativeSource={RelativeSource Mode=FindAncestor, AncestorType=DataGridColumnHeader}}">
        </MenuItem></ContextMenu>
    <Style TargetType="{x:Type DataGridColumnHeader}">
        <Setter Property="ContextMenu" Value="{StaticResource DataGridColumnHeaderMenu}" />
    </Style>
</DataGrid.Resources>

ViewModel：

public ICommand GroupColumn
{
    get
    {
        if (groupColumn == null)
        {
            groupColumn = new RelayCommand( (param) => {

                    UngroupColumns.Execute(null);
                    string groupPropertyName = param as string;   ///Don't want this Switch. ViewModel doesn't know name of the header

                    switch (groupPropertyName)
                    {
                        case "Project": {groupPropertyName = "project_id"; break;}
                        case "Date":    {groupPropertyName = "date";       break;}
                        case "Person":  {groupPropertyName = "person_id";  break;}
                        default:        {groupPropertyName = null; break;        }
                    }

                    if (groupPropertyName != null)
                    {
                        MyData.GroupDescriptions.Add(new PropertyGroupDescription(groupPropertyName));
                        MyData.SortDescriptions.Add(new SortDescription(groupPropertyName, ListSortDirection.Ascending));
                    }
                });
        }

        return groupColumn;
    }
}

Answer 1

因此，我终于找到了解决问题的方法，这里。但是，我仍然不明白为什么CommandParameters在尝试使用：

CommandParameter="{Binding RelativeSource={RelativeSource Mode=FindAncestor, AncestorType={x:Type DataGridColumnHeader}}, Path=Column.SortMemberPath}"

下面是适用于我的代码：

<DataGrid.Resources>    
<ContextMenu x:Key="DataGridColumnHeaderMenu">
    <MenuItem Name="mi_group" Header="Make Groups"                                             
              Command="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type local:MainWindow}}, Path=DataContext.GroupColumn}"
              CommandParameter="{Binding RelativeSource={RelativeSource Mode=FindAncestor, AncestorType={x:Type ContextMenu}}, Path=PlacementTarget.Column.SortMemberPath}">                        
        <MenuItem.Icon>
            <Image Source="images/Treeview.png" />
        </MenuItem.Icon>
    </MenuItem>     
</ContextMenu>
<Style TargetType="{x:Type DataGridColumnHeader}">
    <Setter Property="ContextMenu" Value="{StaticResource DataGridColumnHeaderMenu}" />
</Style></DataGrid.Resources>

在我的例子中使用SortMemberPath的优点是我也可以为DataGridComboxColumn检索一个值(SelectedValuePath)。假设SelectedValuePath等于SortMemberPath，在我的例子中是这样的。

ViewModel：

    private RelayCommand groupColumn;
public ICommand GroupColumn
{
    get
    {
        if (groupColumn == null)
            groupColumn = new RelayCommand(
                (param) =>
                {
                    UngroupColumns.Execute(null);

                    // param contains SortMemberPath of the DataGridColumn
                    string groupPropertyName = param as string;

                    if (groupPropertyName != null)
                    {
                        MyData.GroupDescriptions.Add(new PropertyGroupDescription(groupPropertyName));
                        MyData.SortDescriptions.Add(new SortDescription(groupPropertyName, ListSortDirection.Ascending));
                    }

                });

        return groupColumn;
    }
}