ComboBox水印 提示（IsEditable="True"）

1.Xaml 代码：

<ComboBox>

<ComboBox.Style>
<Style TargetType="ComboBox">
<Style.Triggers>

<MultiTrigger>

<MultiTrigger.Conditions>
<Condition Property="Text" Value=""></Condition>
<Condition Property="IsKeyboardFocusWithin" Value="False"></Condition>                                                                
</MultiTrigger.Conditions>
<Setter Property="Background">
<Setter.Value>
<VisualBrush AlignmentX="Left" AlignmentY="Top" Stretch="None">
<VisualBrush.Visual>
<TextBlock Padding="5,2" Margin="5,0,0,0" Width="240" Height="30"  Background="White" Foreground="Silver"  FontSize="14">请输入用户名</TextBlock>
</VisualBrush.Visual>
</VisualBrush>
</Setter.Value>
</Setter>
</MultiTrigger>
</Style.Triggers>
</Style>                                                
</ComboBox.Style>

</ComboBox>

2.Cs代码

Cs代码针对Text属性，text默认值“”。但是在程序中初始值是NULL，对Null做一下处理就可以了