如何使用Win32功能的VBA找到文本框的文本？

Question

我正在尝试使用VBA从程序中获取文本。我正在使用Win32编程并捕获手柄，并尝试使用常数发送消息。我简化了我正在使用的代码，并将其放在下面。

我遇到麻烦的部分是WM_GetText消息。运行几秒钟后，该行代码崩溃了程序。

根据我的研究，ThunderRT6意味着目标程序是用VB 6制成的。

Private Declare PtrSafe Function FindWindow Lib "user32.dll" Alias "FindWindowA" (ByVal lpClassName As String, ByVal lpWindowName As String) As Long

Private Declare PtrSafe FindWindowEx Lib "user32.dll" Alias "FindWindowExA" (ByVal hWnd1 As Long, ByVal hWnd2 As Long, ByVal lpsz1 As String, ByVal lpsz2 As String) As Long

Private Declare Function SendMessage Lib "user32.dll" Alias "SendMessageA" (ByVal hwnd As Long, ByVal wMsg As Long, ByVal wParam As Long, ByRef lParam As Any) As Long

Private Const WM_GETTEXT As Long = &HD
Private Const WM_GETTEXTLENGTH As Long = &HE


Sub GetTextFromTextBox()
Dim hwnd As Long, myTxtBox As Long
  hwnd = FindWindow(vbNullString, "My Window")
  myTxtBox = FindWindowEx(hwnd, 0&, "ThunderRT6TextBox", vbNullString)

Dim myBuffer As String
Dim myPtr As Long
  myPtr = VarPtr(myBuffer)
Dim myLen As Long
  myLen = SendMessage(myTxtBox, WM_GETTEXTLENGTH, 0, ByVal 0&)
  Debug.Print SendMessage(myTxtBox, WM_GETTEXT, myLen, ByVal myPtr)
End Sub