如何识别 WPF 文本框中的 ValidationError 工具提示位置

我添加了一个箭头来指示工具提示中的文本框。当文本框远离屏幕边缘时，这非常有效。但是当它靠近屏幕边缘时。工具提示位置发生变化，箭头显示在左侧。

Here is the Image Correct as expected, since TextBox in away from edges.

但是当 TextBox 靠近边缘时。我看到这个

我想看到工具提示右侧第二张图片中的箭头。

这是代码

<Grid Grid.Column="0" Width="10"
        Margin="1,0,-1,0"
        Background="Transparent">
    <Path Height="15" Stretch="Fill"
            Fill="{DynamicResource ControlsValidationBrush}"
            Data="F1 M 287.328,237.333L 319.344,255.818L 319.344,218.849L 287.328,237.333 Z " />
</Grid>
<Border Grid.Column="1"
        Background="{DynamicResource ControlsValidationBrush}"
        CornerRadius="0">
    <TextBlock MaxWidth="250"
                Margin="8,7,8,7"
                Foreground="{DynamicResource WhiteBrush}"
                Text="{Binding (Validation.Errors)[0].ErrorContent}"
                TextWrapping="Wrap"
                UseLayoutRounding="false" />
</Border>

我创建了Controltemplate对于工具提示，并根据工具提示的位置显示/隐藏向右或向左箭头。这是它的 Xaml：

       <ControlTemplate x:Key="tooltipTemplate" TargetType="{x:Type ToolTip}">
            <StackPanel Orientation="Horizontal">
                <Grid x:Name="LeftGrid"  
                        Width="10"
                            Margin="1,0,-1,0"
                            Background="Transparent">
                    <Path Height="15" Stretch="Fill"
                                Fill="Red"
                                Data="F1 M 287.328,237.333L 319.344,255.818L 319.344,218.849L 287.328,237.333 Z " />

                </Grid>
                <Border 
                            Background="Red"
                            CornerRadius="0">
                    <TextBlock MaxWidth="250"
                                        Margin="8,7,8,7"
                                        Foreground="{DynamicResource WhiteBrush}"
                                        Text="This is tooltip"
                                        TextWrapping="Wrap"
                                        UseLayoutRounding="false" />
                </Border>
                <Grid x:Name="RightGrid"   Width="10"
                          Margin="1,0,-1,0"
                          Background="Transparent">
                    <Path Height="15" Stretch="Fill"
                                Fill="Red"
                                Data="F1 M 287.328,237.333L 319.344,255.818L 319.344,218.849L 287.328,237.333 Z " />

                </Grid>
            </StackPanel>
            <ControlTemplate.Triggers>
                <Trigger Property="Placement" Value="Left">
                    <Setter TargetName="LeftGrid" Property="Visibility" Value="Hidden"/>
                    <Setter TargetName="RightGrid" Property="Visibility" Value="Visible"/>
                </Trigger>
                <Trigger Property="Placement" Value="Right">
                    <Setter TargetName="LeftGrid" Property="Visibility" Value="Visible"/>
                    <Setter TargetName="RightGrid" Property="Visibility" Value="Hidden"/>
                </Trigger>
            </ControlTemplate.Triggers>
        </ControlTemplate>

   <ToolTip x:Key="myToolTip" Template="{StaticResource tooltipTemplate}">

Thanks