WPF Placeholder TextBox

 

<Grid>
    <TextBox Width="270"  VerticalAlignment="Center" HorizontalAlignment="Left" x:Name="WaterMakrTextBox"/>
    <TextBlock IsHitTestVisible="False" Text="Water Mark Text" VerticalAlignment="Center" HorizontalAlignment="Left" Foreground="LightGray">
        <TextBlock.Style>
            <Style TargetType="{x:Type TextBlock}">
                <Setter Property="Visibility" Value="Collapsed"/>
                <Style.Triggers>
                    <DataTrigger Binding="{Binding Text, ElementName=WaterMakrTextBox}" Value="">
                        <Setter Property="Visibility" Value="Visible"/>
                    </DataTrigger>
                </Style.Triggers>
            </Style>
        </TextBlock.Style>
    </TextBlock>
</Grid>