纯 XAML:
<Grid>
<TextBox Width="250" VerticalAlignment="Center" HorizontalAlignment="Left" x:Name="SearchTermTextBox" Margin="5"/>
<TextBlock IsHitTestVisible="False" Text="Enter Search Term Here" VerticalAlignment="Center" HorizontalAlignment="Left" Margin="10,0,0,0" Foreground="DarkGray">
<TextBlock.Style>
<Style TargetType="{x:Type TextBlock}">
<Setter Property="Visibility" Value="Collapsed"/>
<Style.Triggers>
<DataTrigger Binding="{Binding Text, ElementName=SearchTermTextBox}" Value="">
<Setter Property="Visibility" Value="Visible"/>
</DataTrigger>
</Style.Triggers>
</Style>
</TextBlock.Style>
</TextBlock>
</Grid>
取自:https ://stackoverflow.com/a/21672408/4423545