Wpf TextBox 如何简单粗暴的实现水印效果?

<Border Background="#F3F6F9" Height="50" Width="400"                     CornerRadius="10" HorizontalAlignment="Stretch">                 <Grid Height="Auto">                     <Grid.ColumnDefinitions>                         <ColumnDefinition Width="50"/>                         <ColumnDefinition Width="*"/>                     </Grid.ColumnDefinitions> 　　　　　　　　　　　　<!--请将 Image 的属性 Source 修改为自己的项目路径-->                     <Image Source="/Sample;component/Resources/search.png" Width="25" Stretch="Uniform"/>                     <TextBox Grid.Column="1" x:Name="searchQuery" HorizontalAlignment="Stretch" VerticalAlignment="Stretch" VerticalContentAlignment="Center" TextAlignment="Left" BorderThickness="0" Background="Transparent"/>                     <TextBlock Grid.Column="1" Margin="3,0,0,0" Text="请输入搜索内容..." FontWeight="Bold" HorizontalAlignment="Left" TextAlignment="Left" VerticalAlignment="Center" Foreground="LightGray" IsHitTestVisible="False">                         <TextBlock.Style>                             <Style TargetType="{x:Type TextBlock}">                                 <Setter Property="Visibility" Value="Collapsed"/>                                 <Style.Triggers>                                     <DataTrigger Binding="{Binding Text, ElementName=searchQuery}" Value="">                                         <Setter Property="Visibility" Value="Visible"/>                                     </DataTrigger>                                 </Style.Triggers>                             </Style>                         </TextBlock.Style>                     </TextBlock>                 </Grid>             </Border>