WPF实现TextBox水印效果

通常情况下，在使用文本框的时候，一般会在文本框上放一段水印文字，今天用WPF来实现一下

一般像这种常用的，最好是自己写成用户控件，防止复制粘贴大量冗余代码

<TextBox x: 
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
             xmlns:local="clr-namespace:CallCenter.UserControl"
             mc:Ignorable="d" 
             d:DesignHeight="450" d:DesignWidth="800" Name="MyTextbox">
    <TextBox.Background>
        <VisualBrush Stretch="None" AlignmentX="Left">
            <VisualBrush.Visual>
                <Border DataContext="{Binding ElementName=MyTextbox}" Background="White"  
                        Height="{Binding Path=ActualHeight}">
                    <TextBlock Text="{Binding ElementName=MyTextbox,Path=TipText}"
                               VerticalAlignment="{Binding ElementName=MyTextbox,Path=VerticalContentAlignment}">
                        <TextBlock.Style>
                            <Style TargetType="TextBlock">
                                <Setter Property="Opacity" Value="0"/>
                                <Style.Triggers>
                                    <DataTrigger Binding="{Binding ElementName=MyTextbox,Path=Text}" Value="">
                                        <Setter Property="Opacity" Value="0.2"/>
                                    </DataTrigger>
                                </Style.Triggers>
                            </Style>
                        </TextBlock.Style>
                    </TextBlock>
                </Border>
            </VisualBrush.Visual>
        </VisualBrush>
    </TextBox.Background>
</TextBox>

    /// <summary>
    /// TipTextbox.xaml 的交互逻辑
    /// </summary>
    public partial class TipTextbox : TextBox
    {
        public TipTextbox()
        {
            InitializeComponent();
        }

        public string TipText
        {
            get { return (string)GetValue(TipTextProperty); }
            set { SetValue(TipTextProperty, value); }
        }

        public static readonly DependencyProperty TipTextProperty =
            DependencyProperty.Register("TipText", typeof(string), typeof(TipTextbox), new PropertyMetadata(""));
    }

xmlns:uc="clr-namespace:CallCenter.UserControl"

<uc:TipTextbox TipText="请输入账号" />