1.首先自定义tooltip的controlTemplate，完全清除系统默认效果， 如下：
<ControlTemplate x:Key ="TooltipTemplate" TargetType="ToolTip">
<ContentPresenter x :Name="contentPresenter" Height="{TemplateBinding Height }" Width="{ TemplateBinding Width}" ContentTemplate="{TemplateBinding ContentTemplate }" ></ContentPresenter>
</ControlTemplate>
2.自定义tooltip的contentTemplate， 这样可以专注于tooltip的界面呈现， 而不关心tooltip要显示的字符串， 如下：
<Style x :Key="ToolTipStyle" TargetType="ToolTip">
<Setter Property ="IsOpen" Value="False">
</Setter>
<Setter Property ="ContentTemplate">
<Setter.Value>
<DataTemplate>
<Border x :Name="errorBorder" Background="#CC595959" BorderBrush="#99000000" BorderThickness="1" CornerRadius ="3" HorizontalAlignment="Stretch" VerticalAlignment="Stretch" Margin ="0" MaxWidth="320">
<Border.Effect>
<DropShadowEffect BlurRadius ="4" ShadowDepth="0"/>
</Border.Effect>
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition Width ="Auto"/>
<ColumnDefinition Width ="*"/>
</Grid.ColumnDefinitions>
<Border Margin ="16,16,8,16" VerticalAlignment="Top">
<Path x :Name="path1" Grid.ColumnSpan="1" Data="M9.0789473,12.870737 L10.927632,12.870737 10.927632,14.5 9.0789473,14.5 z M9.0000001,5.9999999 L11,5.9999999 11,7.994543 10.526316,12.308322 9.4802633,12.308322 9.0000001,7.994543 z M9.9647158,1.8074455 C9.5912184,1.7923756 9.2860216,2.1402843 9.2860216,2.1402845 9.2860216,2.1402843 2.5977592,14.8926 2.2227221,15.46075 1.8476844,16.028899 2.5562553,16.218284 2.5562553,16.218284 2.5562553,16.218284 16.2035,16.218284 17.18278,16.218284 18.162063,16.218284 17.870029,15.460751 17.870029,15.460751 17.870029,15.460751 11.056506,2.8352754 10.494117,2.1197443 10.31837,1.8961406 10.134488,1.8142953 9.9647158,1.8074455 z M9.9331295,0.00021409988 C10.317457,0.0076069832 10.762559,0.20740509 11.244278,0.77299643 12.785778,2.5828881 19.97391,16.249695 19.97391,16.249695 19.97391,16.249695 20.318179,17.954408 18.505573,17.985971 16.692966,18.017535 1.5982747,17.985971 1.5982747,17.985971 1.5982747,17.985971 -0.27740097,18.206807 0.03512764,16.028899 0.3476572,13.850991 8.5362361,0.89893103 8.536236,0.8989315 8.5362361,0.89893103 9.0876089,-0.016049385 9.9331295,0.00021409988 z" Height="17" Stretch="Fill" Width="20" Visibility="Visible" Fill ="Red"/>
</Border>
<TextBlock x :Name="textBlock" Text="{TemplateBinding Content }" Margin="0,14,10,14" FontSize="14" Grid.Column ="1" TextWrapping="Wrap" Foreground="Red"/>
</Grid>
</Border>
</DataTemplate>
</Setter.Value>
</Setter>
<Style.Triggers>
<Trigger Property ="IsOpen" Value="True">
<Trigger.EnterActions>
<BeginStoryboard>
<Storyboard>
<ObjectAnimationUsingKeyFrames Storyboard.TargetProperty="Visibility" Duration="0:0:3">
<DiscreteObjectKeyFrame KeyTime ="0:0:0">
<DiscreteObjectKeyFrame.Value>
<Visibility> Visible</Visibility >
</DiscreteObjectKeyFrame.Value>
</DiscreteObjectKeyFrame>
<DiscreteObjectKeyFrame KeyTime ="0:0:3">
<DiscreteObjectKeyFrame.Value>
<Visibility> Hidden</Visibility >
</DiscreteObjectKeyFrame.Value>
</DiscreteObjectKeyFrame>
</ObjectAnimationUsingKeyFrames>
</Storyboard>
</BeginStoryboard>
</Trigger.EnterActions>
</Trigger>
</Style.Triggers>
</Style>
3.应用Tooltip的style，如下：
<Button Content ="TestButton">
< Button.ToolTip>
< ToolTip Style ="{ DynamicResource ToolTipStyle}" Content="This is a button"></ ToolTip >
</ Button.ToolTip>
</ Button>
4.以上style使用时的注意事项：
因为Animation的设置值优先于本地设置值，所以会出现ToolTip在动画结束时永远隐藏。
因此在需要打开tooltip时，首先要在动画开始时设置Visibility为Visible，第二要触发IsOpen=True则必须先IsOpen=False， 因为在Tooltip隐藏后并没有设置IsOpen=False。
代码如下：
_toolTip.Style = ToolTipStyle;
_toolTip.PlacementTarget = this.AssociatedObject;
_toolTip.Placement = PlacementMode.Bottom;
_toolTip.Content = toolTipText;
//must set false first to trigger storyboard
_toolTip.IsOpen = false;
_toolTip.IsOpen = true;
_toolTip.StaysOpen = false;
5.ToolTip的bug
对于ToolTip的显示延迟、显示时间长度、是否保持显示、显示时的位置等等，通用的做法都是通过ToolTipService来进行统一设置。比如：
ToolTipService.InitialShowDelay="1000" ToolTipService.ShowDuration="7000" ToolTipService.BetweenShowDelay="2000" ToolTipService.Placement="Right" ToolTipService.PlacementRectangle="50,0,0,0" ToolTipService.HorizontalOffset="10" ToolTipService.VerticalOffset="20" ToolTipService.HasDropShadow="false" ToolTipService.ShowOnDisabled="true" ToolTipService.IsEnabled="true"
但是，我发现在TextBox的PreviewInput事件里去弹出tooltip时， 以上的ToolTipService设置并没有起到效果，Tooltip的弹出位置和显示时间还是默认的， 即跟随鼠标显示，默认5s。
这个时候就需要对ToolTip的相关属性进行设置。
_toolTip.Style = ToolTipStyle;
_toolTip.PlacementTarget = this.AssociatedObject;
_toolTip.Placement = PlacementMode.Bottom;
当然，当我们toolTip和ToolTipService都设置相关属性时， ToolTipService的设置优先。