WPF中DataGrid列头无法实现本地化绑定的问题求助

我的ComboBox可以完美切换按钮内容，代码如下：

<ComboBox Margin="2 0 0 0" x:Name="languageComboBox" SelectedItem="{Binding SelectedLanguage,Mode=TwoWay}">
    <ComboBoxItem Content="English" Tag="en-US"/>
    <ComboBoxItem Content="Japanese" Tag="jp-JP" />
</ComboBox>

但我无法切换DataGrid的列头内容，试了多种写法都失败了——比如把Id绑定到Label的Content属性能正常工作，但绑定到DataGrid列头就不行。

我试过的两种写法：
第一种：

</DataGrid>
<DataGrid AutoGenerateColumns="False">
    <DataGrid.Columns>
        <DataGridTextColumn HeaderStringFormat="{Binding Id}" Binding="{Binding Id}"/>
        <DataGridTextColumn HeaderStringFormat="{Binding Name}" Binding="{Binding Name}"/>
        <DataGridTextColumn HeaderStringFormat="{Binding Address}" Binding="{Binding Address}"/>
    </DataGrid.Columns>
</DataGrid>

第二种：

</DataGrid>
<DataGrid AutoGenerateColumns="False">
    <DataGrid.Columns>
        <DataGridTextColumn Header="{Binding Id}" Binding="{Binding Id}"/>
        <DataGridTextColumn Header="{Binding Name}" Binding="{Binding Name}"/>
        <DataGridTextColumn Header="{Binding Address}" Binding="{Binding Address}"/>
    </DataGrid.Columns>
</DataGrid>

运行时会抛出如下错误：

System.Windows.Data Error: 2 : Cannot find governing FrameworkElement
or FrameworkContentElement for target element.
BindingExpression:Path=Id; DataItem=null; target element is
'DataGridTextColumn' (HashCode=654914); target property is
'HeaderStringFormat' (type 'String')

问题根源 #

WPF里DataGridColumn不属于可视化树的一部分，没法直接继承DataGrid的DataContext，所以绑定找不到数据源，这就是报错的原因。

解决方法 #

方法1：用绑定代理（Freezable）共享DataContext #

先创建一个继承自Freezable的类，用来保存DataContext：

public class BindingProxy : Freezable
{
    protected override Freezable CreateInstanceCore()
    {
        return new BindingProxy();
    }

    public object Data
    {
        get { return GetValue(DataProperty); }
        set { SetValue(DataProperty, value); }
    }

    public static readonly DependencyProperty DataProperty =
        DependencyProperty.Register("Data", typeof(object), typeof(BindingProxy), new UIPropertyMetadata(null));
}

在XAML的资源里声明这个代理：

<Window.Resources>
    <local:BindingProxy x:Key="ViewModelProxy" Data="{Binding}" />
</Window.Resources>

然后在列头绑定中引用这个代理：

<DataGrid AutoGenerateColumns="False">
    <DataGrid.Columns>
        <DataGridTextColumn Header="{Binding Data.Id, Source={StaticResource ViewModelProxy}}" Binding="{Binding Id}"/>
        <DataGridTextColumn Header="{Binding Data.Name, Source={StaticResource ViewModelProxy}}" Binding="{Binding Name}"/>
        <DataGridTextColumn Header="{Binding Data.Address, Source={StaticResource ViewModelProxy}}" Binding="{Binding Address}"/>
    </DataGrid.Columns>
</DataGrid>

方法2：直接指定DataContext来源 #

如果ViewModel挂在Window/UserControl的DataContext上，可以通过ElementName或RelativeSource指定：

<DataGrid AutoGenerateColumns="False" x:Name="MyDataGrid">
    <DataGrid.Columns>
        <DataGridTextColumn Header="{Binding DataContext.Id, ElementName=MyDataGrid}" Binding="{Binding Id}"/>
        <DataGridTextColumn Header="{Binding DataContext.Name, ElementName=MyDataGrid}" Binding="{Binding Name}"/>
        <DataGridTextColumn Header="{Binding DataContext.Address, ElementName=MyDataGrid}" Binding="{Binding Address}"/>
    </DataGrid.Columns>
</DataGrid>

或者用RelativeSource：

<DataGridTextColumn Header="{Binding DataContext.Id, RelativeSource={RelativeSource AncestorType=Window}}" Binding="{Binding Id}"/>

方法3：用DataTemplate定义列头 #

把列头内容放到DataTemplate里，这样就能正常继承DataContext：

<DataGrid AutoGenerateColumns="False">
    <DataGrid.Columns>
        <DataGridTextColumn Binding="{Binding Id}">
            <DataGridTextColumn.HeaderTemplate>
                <DataTemplate>
                    <TextBlock Text="{Binding DataContext.Id, RelativeSource={RelativeSource AncestorType=DataGrid}}"/>
                </DataTemplate>
            </DataGridTextColumn.HeaderTemplate>
        </DataGridTextColumn>
        <DataGridTextColumn Binding="{Binding Name}">
            <DataGridTextColumn.HeaderTemplate>
                <DataTemplate>
                    <TextBlock Text="{Binding DataContext.Name, RelativeSource={RelativeSource AncestorType=DataGrid}}"/>
                </DataTemplate>
            </DataGridTextColumn.HeaderTemplate>
        </DataGridTextColumn>
        <DataGridTextColumn Binding="{Binding Address}">
            <DataGridTextColumn.HeaderTemplate>
                <DataTemplate>
                    <TextBlock Text="{Binding DataContext.Address, RelativeSource={RelativeSource AncestorType=DataGrid}}"/>
                </DataTemplate>
            </DataGridTextColumn.HeaderTemplate>
        </DataGridTextColumn>
    </DataGrid.Columns>
</DataGrid>

内容的提问来源于stack exchange，提问作者haides