Siverlight去掉ToolTip的白色边框

control作为tooltip后，外框背景是白色的，并且有边框。  我们可以定义 一个样式去掉。

<Style x:Key="ToolTipTransparentStyle" TargetType="ToolTip">
        <Setter Property="Background" Value="#FFF7F8FA"/>
        <Setter Property="Padding" Value="0,0,0,0"/>
        <Setter Property="BorderThickness" Value="0"/>
        <Setter Property="BorderBrush">
            <Setter.Value>
                <LinearGradientBrush EndPoint="0.5,1" StartPoint="0.5,0">
                    <GradientStop Color="#FFA3AEB9" Offset="0"/>
                    <GradientStop Color="#FF8399A9" Offset="0.375"/>
                    <GradientStop Color="#FF718597" Offset="0.375"/>
                    <GradientStop Color="#FF617584" Offset="1"/>
                </LinearGradientBrush>
            </Setter.Value>
        </Setter>
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="ToolTip">
                    <Border x:Name="Root" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" CornerRadius="2">
                        <Border BorderThickness="1" CornerRadius="1" Padding="{TemplateBinding Padding}">
                            <Border.Resources>
                                <Storyboard x:Key="Visible State"/>
                                <Storyboard x:Key="Normal State"/>
                            </Border.Resources>
                            <ContentPresenter Cursor="{TemplateBinding Cursor}" ContentTemplate="{TemplateBinding ContentTemplate}" Content="{TemplateBinding Content}" Margin="{TemplateBinding Padding}"/>
                        </Border>
                    </Border>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>

在创建 ToolTip实例的时候，把ToolTip.Style 用上这个样式就可以了。

参考：http://www.cnblogs.com/eagle1986/archive/2012/05/12/2497189.html