爲什麼下面的代碼不工作？ - 在XAML空指針異常

Question

我在setter中的targetname上得到一個空指針異常，我在其中設置focusmanager.focuselement屬性。我不確定它爲什麼不起作用。任何幫助，將不勝感激。

<Style x:Key="DesignerItemStyle" TargetType="ContentControl"> 
     <Setter Property="MinHeight" Value="50"/> 
     <Setter Property="MinWidth" Value="50"/> 
     <Setter Property="RenderTransformOrigin" Value="0.5,0.5"/> 
     <Setter Property="Template"> 
      <Setter.Value> 
       <ControlTemplate TargetType="ContentControl"> 
        <Grid DataContext="{Binding RelativeSource={RelativeSource TemplatedParent}}"> 
         <s:MoveThumb Template="{StaticResource MoveThumbTemplate}" Cursor="SizeAll"/> 
         <Control x:Name="ResizeDecorator" Template="{StaticResource ResizeDecoratorTemplate}" Visibility="Collapsed"/> 
         <ContentPresenter Content="{TemplateBinding ContentControl.Content}"/> 
         <TextBox x:Name="textboxName" Text="node" Background="Transparent" BorderBrush="Transparent" BorderThickness="0" HorizontalAlignment="Center" VerticalAlignment="Center" Width="Auto" Height="Auto" IsHitTestVisible="False"/> 
         <TextBox x:Name="count" Text="100" Background="Transparent" BorderBrush="Transparent" BorderThickness="0" HorizontalAlignment="Right" VerticalAlignment="Bottom" Width="Auto" Height="Auto" IsHitTestVisible="False"/> 
        </Grid> 
        <ControlTemplate.Triggers> 
         <Trigger Property="IsKeyboardFocused" Value="True"> 
          <Setter TargetName="ResizeDecorator" Property="Visibility" Value="Visible"/> 
         </Trigger> 
         <Trigger Property="IsManipulationEnabled" Value="True"> 
          <Setter TargetName="textboxName" Property="IsHitTestVisible" Value="True"/> 
          <Setter TargetName="textboxName" Property="FocusManager.FocusedElement" Value="textboxName"/> 
         </Trigger> 
        </ControlTemplate.Triggers> 
       </ControlTemplate> 
      </Setter.Value> 
     </Setter> 
    </Style> 

Answer 1

我在代碼中看不到目標名稱。開始刪除樣式的部分，直到編譯以縮小問題的範圍。