WPF：如何通过控件模板内按钮纯XAML清除TextBox文本

问题根源 #

你使用IsPressed触发器无效，是因为按钮点击时焦点会发生转移，触发器的条件无法持续满足；同时普通Setter在交互场景下的属性优先级规则，导致直接设置Text的操作不生效。

最优方案：利用WPF内置清除命令 #

直接给清除按钮绑定ApplicationCommands.Clear，TextBox原生支持该命令，无需额外代码就能实现清除逻辑，完美适配现有模板的交互规则：

修改按钮XAML，添加Command属性：

<Button x:Name="ClearSearchText"
        Margin="5,0,6,0"
        Grid.Column="2"
        Background="Transparent"
        BorderBrush="Transparent"
        BorderThickness="0"
        Cursor="Hand"
        FontFamily="{Binding Font, Source={StaticResource ResourceKey=Icons}}"
        HorizontalAlignment="Right"
        VerticalAlignment="Center"
        Command="{x:Static ApplicationCommands.Clear}">
    <!-- 按钮内容保持不变 -->
</Button>

之后删除原来无效的IsPressed触发器即可。按钮点击时，内置命令会自动清除TextBox文本，现有触发器会因为Text变为空自动隐藏按钮，完全契合需求。

备选方案：用EventTrigger+动画设置Text #

如果偏好触发器实现方式，可将无效的IsPressed触发器替换为按钮Click事件的EventTrigger，通过动画强制设置Text属性：

<EventTrigger SourceName="ClearSearchText" RoutedEvent="Button.Click">
    <BeginStoryboard>
        <Storyboard>
            <ObjectAnimationUsingKeyFrames Storyboard.TargetProperty="Text">
                <DiscreteObjectKeyFrame KeyTime="0:0:0" Value="{x:Null}"/>
            </ObjectAnimationUsingKeyFrames>
        </Storyboard>
    </BeginStoryboard>
</EventTrigger>

这种方式通过动画绕开普通Setter的属性优先级限制，确保Text被成功清空。

完整修改后的ControlTemplate（最优方案版本） #

<ControlTemplate x:Key="SearchTextBoxTemplate" TargetType="{x:Type TextBox}">
    <Border Background="{TemplateBinding Background}"
            BorderBrush="{TemplateBinding BorderBrush}"
            BorderThickness="{TemplateBinding BorderThickness}"
            CornerRadius="5"
            SnapsToDevicePixels="True">
        <Grid HorizontalAlignment="Stretch"
              VerticalAlignment="Stretch">
            <Grid.ColumnDefinitions>
                <ColumnDefinition Width="Auto"/>
                <ColumnDefinition Width="*"/>
                <ColumnDefinition Width="Auto"/>
            </Grid.ColumnDefinitions>
            <TextBlock Margin="6,1,6,0"
                       Grid.Column="0"
                       FontFamily="{Binding Font, Source={StaticResource Icons}}"
                       FontSize="{TemplateBinding FontSize}"
                       Foreground="#8C8C8C"
                       FontWeight="Normal"
                       Text="&#xE71E;"
                       HorizontalAlignment="Left"
                       VerticalAlignment="Center"/>
            <TextBlock x:Name="Placeholder"
                       Grid.Column="1"
                       FontSize="{TemplateBinding FontSize}"
                       Focusable="False"
                       Text="Search"
                       Foreground="#AAAFB4"
                       IsHitTestVisible="False"
                       HorizontalAlignment="Left"
                       VerticalAlignment="Center"
                       Visibility="Collapsed"/>
            <ScrollViewer x:Name="PART_ContentHost"
                          Grid.Column="1"
                          Focusable="False"
                          HorizontalScrollBarVisibility="Hidden"
                          VerticalScrollBarVisibility="Hidden"
                          VerticalContentAlignment="Center"
                          VerticalAlignment="Center"/>
            <Button x:Name="ClearSearchText"
                    Margin="5,0,6,0"
                    Grid.Column="2"
                    Background="Transparent"
                    BorderBrush="Transparent"
                    BorderThickness="0"
                    Cursor="Hand"
                    FontFamily="{Binding Font, Source={StaticResource ResourceKey=Icons}}"
                    HorizontalAlignment="Right"
                    VerticalAlignment="Center"
                    Command="{x:Static ApplicationCommands.Clear}">
                <Button.Content>
                    <Grid>
                        <TextBlock FontSize="12"
                                   Foreground="#D1D1D1"
                                   Text="&#xE91F;"/>
                        <TextBlock FontSize="8"
                                   HorizontalAlignment="Center"
                                   VerticalAlignment="Center"
                                   Foreground="White"
                                   Text="&#xE711;"/>
                    </Grid>
                </Button.Content>
            </Button>
        </Grid>
    </Border>
    <ControlTemplate.Triggers>
        <Trigger Property="IsEnabled" Value="False">
            <Setter Property="Opacity" Value="0.6"/>
        </Trigger>
        <Trigger Property="Text" Value="{x:Static sys:String.Empty}">
            <Setter TargetName="ClearSearchText" Property="Visibility" Value="Collapsed"/>
        </Trigger>
        <Trigger Property="Text" Value="{x:Null}">
            <Setter TargetName="ClearSearchText" Property="Visibility" Value="Collapsed"/>
        </Trigger>
        <MultiTrigger>
            <MultiTrigger.Conditions>
                <Condition Property="IsKeyboardFocusWithin" Value="False"/>
                <Condition Property="Text" Value="{x:Static sys:String.Empty}"/>
            </MultiTrigger.Conditions>
            <Setter TargetName="Placeholder" Property="Visibility" Value="Visible"/>
        </MultiTrigger>
        <MultiTrigger>
            <MultiTrigger.Conditions>
                <Condition Property="IsKeyboardFocusWithin" Value="False"/>
                <Condition Property="Text" Value="{x:Null}"/>
            </MultiTrigger.Conditions>
            <Setter TargetName="Placeholder" Property="Visibility" Value="Visible"/>
        </MultiTrigger>
    </ControlTemplate.Triggers>
</ControlTemplate>

内容的提问来源于stack exchange，提问作者5ORBEX