WPF DataTemplate DataContext 绑定问题

当使用DataTemplate时，需要用数据绑定，设置数据绑定的方式可参考：

https://supportcenter.devexpress.com/ticket/details/t736087/datacontext-not-available-inside-barbuttonitem-of-datatemplate

<dxb:BarSubItem x:Name="brGroupBy" Content="Group By"  ItemLinksSource="{Binding GroupByAttributes}"   >
                    <dxb:BarSubItem.ItemTemplate>
                        <DataTemplate>
                            <ContentControl >
                                <dxb:BarButtonItem  Content="{Binding DisplayName}"  IsEnabled="{Binding Path=IsEnable}"     >
                                    <DataTemplate>
                                        <dxb:BarButtonItem.ContentTemplate>
                                            <DataTemplate>
                                                <Grid HorizontalAlignment="Left">
                                                    <Grid.ColumnDefinitions>
                                                        <ColumnDefinition Width="*" />
                                                        <ColumnDefinition Width="Auto" />
                                                    </Grid.ColumnDefinitions>
                                                    <TextBlock VerticalAlignment="Center"  Text="{Binding}">
<Image x:Name="positionInformation" Grid.Column="1"
                                       Width="20"
                                       Height="15"
                                    Source="…/…/…/…/Resources/Images/Toast_Blue.png">
                                                        <Image.ToolTip>
                                                            <ToolTip  Style="{StaticResource ToolTipDisplayFormatStyle}" ToolTipService.ShowOnDisabled="True" Content="{Binding Reason}"/>
                                                        </Image.ToolTip>
                                                        <Image.Style>
                                                            <Style>
                                                                    <Setter Property="Control.Visibility" Value="Collapsed" />
                                                                    <Style.Triggers>
                                                                    <MultiDataTrigger>
                                                                        <MultiDataTrigger.Conditions>
                                                                                <Condition Binding="{Binding}" Value="Position"/>
                                                                        </MultiDataTrigger.Conditions>
                                                                        <Setter Property="Control.Visibility" Value="Visible" />
                                                                    </MultiDataTrigger>
                                                                </Style.Triggers>
                                                            </Style>
                                                        </Image.Style>
                                                    </Image>
                                                </Grid>
                                            </DataTemplate>
                                        </dxb:BarButtonItem.ContentTemplate>
                                </dxb:BarButtonItem>
                            </ContentControl>
                        </DataTemplate>
                    </dxb:BarSubItem.ItemTemplate>
                </dxb:BarSubItem>

设置数据绑定属性的方式：

<dxb:BarButtonItem  Content="{Binding}" ...  
--------  
<TextBlock Text="{Binding DisplayName}" ...  
--------  
<ToolTip Content="{Binding Reason}" ...  

Content="{Binding}" 会将 GroupByAttribute  对象设置为ContentTemplate的DataContext;