如何在WPF中将样式触发器应用于datatemplate

I've got the following..

我有以下......

<ComboBox Grid.Row="2" Grid.Column="2" Grid.RowSpan="2" ItemsSource="{Binding ShipperAddresses}" Text="{Binding ShipperAddress}" Margin="85,2,0,2">
    <ComboBox.ItemTemplate>
        <DataTemplate>
            <TextBox AcceptsReturn="True" Width="200" Height="100"/>
            <DataTemplate.Resources>
                <Style TargetType="{x:Type TextBox}">
                    <Setter Property="IsReadOnly" Value="True">
                    <Style.Triggers>
                        <DataTrigger Binding="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type GroupBox}}, Path=Tag}" Value="False"/>
                    </Style.Triggers>
                    </Setter>
                </Style>
            </DataTemplate.Resources>
        </DataTemplate>
    </ComboBox.ItemTemplate>
</ComboBox>
<ComboB