Button是TextBlock？

Question

我使用这个函数来递归遍历ListBoxItem中的所有控件，并且在DataTemplate中既有Button又有TextBlock。它总是选择按钮而不是TextBlock。有人能看到我的函数出了什么问题吗？

Private Function FindVisualChild(ByVal obj As DependencyObject) As TextBlock
 Dim result As TextBlock = Nothing
 For i As Integer = 0 To VisualTreeHelper.GetChildrenCount(obj) - 1
  Dim child As DependencyObject = TryCast(VisualTreeHelper.GetChild(obj, i), DependencyObject)
  If Not child Is Nothing AndAlso TypeOf child Is DependencyObject Then
    If TypeOf child Is TextBlock Then
      Dim tbl As TextBlock = TryCast(child, TextBlock)
      If Not tbl Is Nothing Then result = tbl
    Else
      Dim tbl As TextBlock = FindVisualChild(child)
      If Not tbl Is Nothing Then result = tbl : Exit For
    End If
  End If
Next
Return result

End函数

Answer 1

看起来很简单，但它确实有效！不能解释为什么它会与这条线下面的类型混淆。

Private Function FindVisualChild(ByVal obj As DependencyObject) As TextBlock
Dim result As TextBlock = Nothing
For i As Integer = 0 To VisualTreeHelper.GetChildrenCount(obj) - 1
  Dim child As DependencyObject = TryCast(VisualTreeHelper.GetChild(obj, i), DependencyObject)
  If TypeOf child Is Button Then Continue For 'fixes it
  If Not child Is Nothing AndAlso TypeOf child Is DependencyObject Then
    If TypeOf child Is TextBlock Then
      Dim tbl As TextBlock = TryCast(child, TextBlock)
      If Not tbl Is Nothing Then result = tbl
    Else
      Dim tbl As TextBlock = FindVisualChild(child)
      If Not tbl Is Nothing Then result = tbl : Exit For
    End If
  End If
Next
Return result

End函数