使用c#在wpf中定位弹出窗口

我已经在按钮鼠标悬停上放置了一个弹出窗口.每当我将鼠标悬停在该按钮上时,我的自定义设计弹出窗口就会完美显示.但是它并没有完美地指向按钮.怎么这样..？
现在我的弹出窗口看起来像

我希望箭头标记指向帮助按钮如何实现它..

这是我在xaml中按钮和弹出窗口的代码

<telerik:RadButton Name="btnH" Grid.Column="1" HorizontalAlignment="Left" Margin="444,56,0" Grid.Row="2" VerticalAlignment="Top" 
                 Width="23" Height="23" BorderThickness="6" BorderBrush="#4E4E4E">
            <Image Source="Images/help.png" />
            <telerik:RadButton.Triggers>
                    <EventTrigger RoutedEvent="MouseEnter">
                        <BeginStoryboard>
                        <Storyboard TargetName="TooltipPopup" TargetProperty="IsOpen">
                                <BooleanAnimationUsingKeyFrames  FillBehavior="HoldEnd">
                                    <discreteBooleanKeyFrame KeyTime="00:00:00"  Value="True" />
                                </BooleanAnimationUsingKeyFrames>
                            </Storyboard>
                        </BeginStoryboard>
                    </EventTrigger>

              
            
                
                    
                        
                    
                
            

以下是自定义usercontrol xaml,它在弹出窗口中调用

<UserControl
         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:telerik="http://schemas.telerik.com/2008/xaml/presentation" x:Class="WPFTest.UCToolTip" 
         mc:Ignorable="d" Height="231.493" Width="362.075"
         Background="Transparent"  >
<UserControl.Resources>
    <Style targettype="{x:Type Hyperlink}">
                 <Setter Property="TextBlock.Textdecorations" Value="{x:Null}" />
    </Style>
</UserControl.Resources>
<Grid Margin="10,0">
    <Grid.RowDeFinitions>
        <RowDeFinition/>
        <RowDeFinition Height="Auto"/>
    </Grid.RowDeFinitions>
    <Grid Background="red" Margin="0,182,133">            

    </Grid>
    <polygon
    Points="0.5,0 15,30" stroke="Orange" Fill="Orange" Margin="0,98,101" />
</Grid>

解决方法

将此样式用于弹出窗口：

<Style targettype="Popup">
                <Style.Triggers>
                    <Trigger Property="IsOpen" Value="true">
                        <Setter Property="PlacementTarget" Value="{Binding ElementName=btnH }" />
                        <Setter Property="Placement" Value="Top" />
                        <Setter Property="VerticalOffset" Value="-5" />
                        <Setter Property="HorizontalOffset" Value="5" />
                    </Trigger>
                </Style.Triggers>
            </Style>