WPF - Canvas.Left和Canvas.Top绑定无法正常工作

Question

我正在尝试绑定边框Canvas.Top和Canvas.Left，绑定没有问题，但问题是它没有更新其值。第一步它很有效，但它不适用于其他步骤。

<Border 
   Name="helpBox" 
   CornerRadius="10" 
   Panel.ZIndex="50"
   Background="Black" 
   BorderBrush="Black" 
   BorderThickness="0"
   Height="Auto" 
   Width="580"
   MouseLeftButtonDown="helpBox_MouseLeftButtonDown"
   MouseLeftButtonUp="helpBox_MouseLeftButtonUp" 
   MouseMove="helpBox_MouseMove"
   Canvas.Left="{Binding CurrentTour.CurrentStep.HelpBoxLeft}"
   Canvas.Top="{Binding CurrentTour.CurrentStep.HelpBoxTop}"/>`