Private Const SBS_HORZ = 0
Private Const SBS_VERT = 1

<DllImport("user32.dll")> _
Public Function GetScrollRange(ByVal hWnd As IntPtr,ByVal nBar As Integer,_
                               ByRef lpMinPos As Integer,_
                               ByRef lpMaxPos As Integer) As Boolean
End Function

<DllImport("user32.dll")> _
Public Function GetScrollPos(ByVal hWnd As Integer,_
                             ByVal nBar As Integer) As Integer
End Function

// ...

Dim scrollMin as Integer = 0
Dim scrollMax as Integer = 0

If(GetScrollRange(rtb.Handle,SBS_VERT,scrollMin,scrollMax) Then
   Dim pos as Integer = GetScrollPos(rtb.Handle,SBS_VERT)

   // Detect if they're at the bottom
EndIf

笔记：

要确定滚动条是否可见,请调用GetWindowLong并检查WS_VSCROLL

要确定滑块可以达到的最大值,请调用GetScrollInfo;我认为最大值是

scrollMax - largeChange + 1