当Validation.HasError为True时显示元素的WPF触发器问题求助

以下是我使用的XAML标记：

<GroupBox Margin="10" Padding="20" Header="Case 5 - Custom Error Object">
    <GroupBox.DataContext>
        <local:ViewModel4/>
    </GroupBox.DataContext>
    <StackPanel>
        <Label Name="AdornerElement" Style="{StaticResource ResourceKey=AdornerElementStyle}"/>
        <TextBox Text="{Binding Path=UserName, UpdateSourceTrigger=PropertyChanged, ValidatesOnNotifyDataErrors=True}"
                 Margin="0 10"
                 Validation.ValidationAdornerSite="{Binding ElementName=AdornerElement}">
        </TextBox>
    </StackPanel>
</GroupBox>

对应的样式代码：

<Style x:Key="AdornerElementStyle" TargetType="Label">
    <Setter Property="Visibility" Value="Collapsed"/>
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="Label">
                <StackPanel Orientation="Horizontal" Background="LightCoral">
                    <Image Source="/clipart.png" Width="24" Margin="10"/>
                    <ItemsControl ItemsSource="{Binding ElementName=AdornerElement, Path=(Validation.ValidationAdornerSiteFor).(Validation.Errors)}"
                              VerticalAlignment="Center">
                        <ItemsControl.ItemTemplate>
                            <DataTemplate>
                                <TextBlock Text="{Binding Path=ErrorContent.ValidationMessage}"
                                           Style="{StaticResource CustomErrorTypeStyle}"/>
                            </DataTemplate>
                        </ItemsControl.ItemTemplate>
                    </ItemsControl>
                </StackPanel>
                <ControlTemplate.Triggers>
                    <DataTrigger Binding="{Binding ElementName=AdornerElement, Path=Validation.HasError}" Value="True">
                        <Setter Property="Visibility" Value="Visible"/>
                    </DataTrigger>
                </ControlTemplate.Triggers>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>

当前问题：除触发器外其他功能均正常——若初始将Visibility设为Visible，错误信息可正常显示；但使用上述样式时，Label始终处于Collapsed状态。

解决方法 #

问题出在触发器的绑定路径上：Label自身的Validation.HasError不会自动关联到TextBox的错误状态，需要绑定到TextBox的Validation.HasError，而Label作为ValidationAdornerSite，其ValidationAdornerSiteFor属性会指向对应的TextBox，因此可以通过该属性获取目标控件的错误状态。

修正后的样式代码如下：

<Style x:Key="AdornerElementStyle" TargetType="Label">
    <Setter Property="Visibility" Value="Collapsed"/>
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="Label">
                <StackPanel Orientation="Horizontal" Background="LightCoral">
                    <Image Source="/clipart.png" Width="24" Margin="10"/>
                    <ItemsControl ItemsSource="{Binding ElementName=AdornerElement, Path=(Validation.ValidationAdornerSiteFor).(Validation.Errors)}"
                              VerticalAlignment="Center">
                        <ItemsControl.ItemTemplate>
                            <DataTemplate>
                                <TextBlock Text="{Binding Path=ErrorContent.ValidationMessage}"
                                           Style="{StaticResource CustomErrorTypeStyle}"/>
                            </DataTemplate>
                        </ItemsControl.ItemTemplate>
                    </ItemsControl>
                </StackPanel>
                <ControlTemplate.Triggers>
                    <!-- 修正：绑定到ValidationAdornerSiteFor指向的控件的HasError状态 -->
                    <DataTrigger Binding="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=(Validation.ValidationAdornerSiteFor).Validation.HasError}" Value="True">
                        <Setter Property="Visibility" Value="Visible"/>
                    </DataTrigger>
                </ControlTemplate.Triggers>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>

修改说明 #

• 将触发器的绑定从ElementName=AdornerElement, Path=Validation.HasError改为RelativeSource={RelativeSource TemplatedParent}, Path=(Validation.ValidationAdornerSiteFor).Validation.HasError
• 通过RelativeSource TemplatedParent获取当前Label控件，再通过(Validation.ValidationAdornerSiteFor)指向关联的TextBox，最终绑定到TextBox的Validation.HasError属性
• 这样当TextBox的验证状态变化时，触发器能正确感知并切换Label的Visibility

内容的提问来源于stack exchange，提问作者vso