Using Native WIN32 APIs in VB; A Message Box Example

Category:

ASP, HTML and XML

Type:

Modules

Difficulty:

Advanced

Author:

Timothy L Slater Jr.

Version Compatibility: Visual Basic 6

More information:

This module will allow you to create a MessageBox using the Native WIN32 API 'MessageBoxW'. The built in MsgBox() function of VB uses the Virtual Machine to create the messagebox, this is a proof of concept showing how it can be done. Using this routine will result in faster code. NOTE: It uses Pre-Compiled Assembler code. To test this, set a variable of type Long to the ntvMessageBox function, passing it the title and message as strings. Email me with questions.

Instructions: Copy the declarations and code below and paste directly into your VB project.

Declarations:
Private Declare Function LoadLibrary Lib "kernel32" Alias "LoadLibraryA" (ByVal lpLibFileName As String) As Long Private Declare Function GetProcAddress Lib "kernel32" (ByVal hModule As Long, ByVal lpProcName As String) As Long Private Declare Function CallWindowProc Lib "user32" Alias "CallWindowProcA" (ByVal lpPrevWndFunc As Long, ByVal hWnd As Long, ByVal Msg As Long, ByVal wParam As Long, ByVal lParam As Long) As Long

Code:

Public Function ntvMessageBox(msgboxTitle As String, msgboxText As String, Optional msgboxStyle As VbMsgBoxStyle = vbOKOnly) As Long
    Dim retValue As Long
    Dim APIOffset As Long
    Dim ret As Long
    Dim ASMString As String
    ret = LoadLibrary("User32.dll")
    ret = GetProcAddress(ret, "MessageBoxW")
    Dim EmptyString As String
    Dim MessageString As String
    EmptyString = msgboxTitle
    MessageString = msgboxText
    Dim ASMArray() As Byte
    ASMString = "609C3E8B442434FF303E8B442434FF303E8B442434FF306A00E8"
    ReDim ASMArray(0 To 39)
    APIOffset = ret - (VarPtr(ASMArray(0)) + (Len(ASMString) / 2)) - 4
    ASMString = ASMString & MakeDword(APIOffset) & "3E8B4C242889019D61C3"
    Call ExecuteASM(ASMString, ASMArray(), VarPtr(retValue), VarPtr(msgboxText), VarPtr(msgboxTitle), VarPtr(msgboxStyle))
    ntvMessageBox = retValue
End Function

Private Sub ExecuteASM(ASMString As String, ByRef ASMArray() As Byte, ReturnValue As Long, Param1 As Long, Param2 As Long, Param3 As Long)
    y = 0
    For x = 0 To Len(ASMString) - 2 Step 2
        ASMArray(y) = Val("&H" & Mid(ASMString, x + 1, 2))
        y = y + 1
    Next x
    Call CallWindowProc(VarPtr(ASMArray(0)), ReturnValue, Param1, Param2, Param3)
End Sub

Public Function MakeDword(theNum As Long) As String
 temp = Hex(theNum)
 If Len(temp) < 8 Then
    temp = String(8 - Len(temp), "0") & temp
 End If
 temp1 = Mid(temp, 7, 2)
 temp1 = temp1 & Mid(temp, 5, 2)
 temp1 = temp1 & Mid(temp, 3, 2)
 temp1 = temp1 & Mid(temp, 1, 2)
    MakeDword = temp1
End Function