使用 SendMessage user32 API 以編程方式滾動 RichTextBox 不能超過整數值

Question

我正在使用 vb2010 WinForm 制作一個文本編輯器應用程序。 不用滾動條滾動，用戶可以直接用鼠標在richtextbox上滾動，類似於adobe acrobat reader。 要以編程方式滾動richtextbox，我正在使用 SendMessage user32 API。

我有兩個問題：

1. 如果richtextbox 中的文本很大並且我在整數值的末尾附近滾動，那么滾動條將滾動回其初始位置。
2. 使用 SendMessage 設置的滾動條值與我們稍后使用 GetScrollPos 讀取時不一樣。 結果，當我使用鼠標拖動文本時，richtextbox 開始時滾動不流暢，它是跳躍的。

這是我所做的：

Public Class Form1
    Dim StartMouseDownPos As New Point
    Dim StartScrollBarPos As New Point
    Const WM_USER = &H400
    Const EM_GETSCROLLPOS = WM_USER + 221
    Const EM_SETSCROLLPOS = WM_USER + 222

    Public Declare Auto Function RtfScroll Lib "user32.dll" Alias "SendMessage" ( _
            ByVal hWnd As IntPtr, _
            ByVal Msg As Integer, _
            ByVal wParam As IntPtr, _
            ByRef lParam As System.Drawing.Point) As Integer

    Private Sub RichTextBox1_MouseDown(ByVal sender As System.Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles RichTextBox1.MouseDown
        'Capture the initial mouse position
        StartMouseDownPos.X = e.X
        StartMouseDownPos.Y = e.Y
        'Capture the initial scrollbar position
        RtfScroll(RichTextBox1.Handle, EM_GETSCROLLPOS, 0, StartScrollBarPos)
    End Sub

    Private Sub RichTextBox1_MouseMove(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles RichTextBox1.MouseMove
        'Verify left button is pressed while the mouse is moving
        If e.Button = Windows.Forms.MouseButtons.Left Then
            'Prevent the text in RichTextBox1 to be unintentionally selected when user dragged the text while the cursor shape at that moment is a hand.
            ActiveControl = Nothing
            NewScrollBarPos.X = StartScrollBarPos.X + (StartMouseDownPos.X - e.X)
            NewScrollBarPos.Y = StartScrollBarPos.Y + (StartMouseDownPos.Y - e.Y)
            RtfScroll(RichTextBox1.Handle, EM_SETSCROLLPOS, 0, NewScrollBarPos)
        End If
    End Sub

我試圖改變上面有問題的陳述： RtfScroll(RichTextBox1.Handle, EM_SETSCROLLPOS, 0, NewScrollBarPos) 如下：

Public Declare Function GetScrollPos Lib "user32.dll" ( _
       ByVal hWnd As IntPtr, _
       ByVal nBar As Integer) As Integer

Public Declare Function SetScrollPos Lib "user32.dll" ( _
       ByVal hWnd As IntPtr, _
       ByVal nBar As Integer, _
       ByVal nPos As Integer, _
       ByVal bRedraw As Boolean) As Integer

Public Declare Function PostMessageA Lib "user32.dll" ( _
       ByVal hwnd As IntPtr, _
       ByVal wMsg As Integer, _
       ByVal wParam As Integer, _
       ByVal lParam As Integer) As Boolean

'Scroll the horizontal scrollbar according to the drag of the mouse
SetScrollPos(RichTextBox1.Handle, SBS_HORZ, NewScrollBarPos.X, True)
SetScrollPos(RichTextBox1.Handle, SBS_VERT, NewScrollBarPos.Y, True)
'Scroll the text according to the drag of the mouse
PostMessageA(RichTextBox1.Handle, WM_HSCROLL, SB_THUMBPOSITION + &H10000 * GetScrollPos(RichTextBox1.Handle, SBS_HORZ), Nothing)
PostMessageA(RichTextBox1.Handle, WM_VSCROLL, SB_THUMBPOSITION + &H10000 * GetScrollPos(RichTextBox1.Handle, SBS_VERT), Nothing)

結果更糟：當我試圖滾動超出整數值時，會在 &H10000 * GetScrollPos(RichTextBox1.Handle, SBS_HORZ), Nothing) 相乘時引發溢出異常。

那么，我的問題是如何解決這兩個問題？

Answer 1

我做了一個小程序來找出問題的原因，結果發現問題是這樣的：使用 Point 作為輸入的RtfScroll函數別名“SendMessage”沒有獲取或設置正確的值。 這不會發生在GetScrollPos 、 SetScrollPos和PostMessageA上。

所以，不要使用RtfScroll(RichTextBox1.Handle, EM_SETSCROLLPOS, 0, New Point(countX, countY)) & RtfScroll(RichTextBox1.Handle, EM_GETSCROLLPOS, 0, point)的組合。

只需使用GetScrollPos 、 SetScrollPos和PostMessageA的組合。