c# - How to identify the ValidationError ToolTip Placement in WPF TextBox -

i have added arrow indicate textbox tooltip. works great when textbox far away screen edge. when near screen edge. tooltip placement changes , arrow shown on left.

here image correct expected, since textbox in away edges.

but when textbox near edges. see this

i want see arrow in second image on right side of tooltip.

here code

<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> 

i created controltemplate tooltip , show/hide right or left arrow depending on placement of tooltip. here xaml it:

       <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 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