如何在DataGrid上设置d：DataContext d：DesignInstance

The xaml:

xaml：

    <Grid.ColumnDefinitions>
        <ColumnDefinition Width="*" />
    </Grid.ColumnDefinitions>
    <Grid.RowDefinitions>
        <RowDefinition Height="auto"/>
        <RowDefinition Height="*"/>
    </Grid.RowDefinitions>

    <TextBox VerticalAlignment="Center" FocusManager.IsFocusScope="True" Grid.ColumnSpan="2" Name="SearchTextBox" Text="{Binding Path=SearchTerm.Value, UpdateSourceTrigger=PropertyChanged}" Style="{StaticResource FontStyle}" KeyUp="SearchTextBoxKeyUp" />

    <DataGrid Grid.Row="1" ItemsSource="{Binding Path=EpisodesView, Mode=TwoWay}" MouseDoubleClick="ListViewDoubleClick" Style="{StaticResource FontStyle}" KeyUp="ListViewKeyup" Name="EpisodeList" AutoGenerateColumns="False" IsReadOnly="True"
              d:DataContext="{d:DesignInstance vm:Episode}">
        <DataGrid.Columns>
            <DataGridTextColumn Header="File" Binding="{Binding File.Name}" />
            <DataGridTextColumn Header="Age" Binding="{Binding PrettyAge}" SortMemberPath="Age" />
        </DataGrid.Columns>
    </DataGrid>
</Grid>
</Window>
    <Grid.ColumnDefinition