使用API创建窗体（类似VC的创建过程）

在VB中用API创建窗体和VC中的步骤是一样的，只不过用IDE环境创建是把过程都封装起来，现在我们用API方式创建，大致让我们了解一个窗体的产生过程，让我们使用VB的程序员对系统的机制多一些了解.
先所以下用C++创建窗体的过程：
程序的入口：int APIENTRY WinMain(HINSTANCE hInstance,
HINSTANCE hPrevInstance,
LPSTR lpCmdLine,
int nCmdShow)
进入后先初始化结构WNDCLASSEX wcex;
调用APIRegisterClassEx,注册窗体结构，如果成功一次调用CreateWindow、ShowWindow、UpdateWindow这样一个主窗体就成功的创建并显示给用户，下面就缺少一个处理消息的死循环。
那么我们我们可以按照这个步骤在VB中实现一样的效果：
在C++因为API声明已经被包涵到头文件所以直接用就可以，但是在VB中就要逐个声明一下用到的API，结构。
Public Declare Function RegisterClass Lib "user32" Alias "RegisterClassA" (Class As WNDCLASS) As Long
Public Declare Function UnregisterClass Lib "user32" Alias "UnregisterClassA" (ByVal lpClassName As String, ByVal hInstance As Long) As Long
Public Declare Function DefWindowProc Lib "user32" Alias "DefWindowProcA" (ByVal hwnd As Long, ByVal wMsg As Long, ByVal wParam As Long, ByVal lParam As Long) As Long
Public Declare Function GetMessage Lib "user32" Alias "GetMessageA" (lpMsg As Msg, ByVal hwnd As Long, ByVal wMsgFilterMin As Long, ByVal wMsgFilterMax As Long) As Long
Public Declare Function TranslateMessage Lib "user32" (lpMsg As Msg) As Long
Public Declare Function DispatchMessage Lib "user32" Alias "DispatchMessageA" (lpMsg As Msg) As Long
Public Declare Function ShowWindow Lib "user32" (ByVal hwnd As Long, ByVal nCmdShow As Long) As Long
Public Declare Function LoadCursor Lib "user32" Alias "LoadCursorA" (ByVal hInstance As Long, ByVal lpCursorName As Any) As Long
Public Declare Function LoadIcon Lib "user32" Alias "LoadIconA" (ByVal hInstance As Long, ByVal lpIconName As String) As Long
Public Declare Function CreateWindowEx Lib "user32" Alias "CreateWindowExA" (ByVal dwExStyle As Long, ByVal lpClassName As String, ByVal lpWindowName As String, ByVal dwStyle As Long, ByVal x As Long, ByVal y As Long, ByVal nWidth As Long, ByVal nHeight As Long, ByVal hWndParent As Long, ByVal hMenu As Long, ByVal hInstance As Long, lpParam As Any) As Long
Public 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
Public Declare Function SetWindowLong Lib "user32" Alias "SetWindowLongA" (ByVal hwnd As Long, ByVal nIndex As Long, ByVal dwNewLong As Long) As Long
Public Declare Function GetWindowLong Lib "user32" Alias "GetWindowLongA" (ByVal hwnd As Long, ByVal nIndex As Long) As Long
Public Declare Function MessageBox Lib "user32" Alias "MessageBoxA" (ByVal hwnd As Long, ByVal lpText As String, ByVal lpCaption As String, ByVal wType As Long) As Long
Public Declare Sub PostQuitMessage Lib "user32" (ByVal nExitCode As Long)

Public Type WNDCLASS
style As Long
lpfnwndproc As Long
cbClsextra As Long
cbWndExtra2 As Long
hInstance As Long
hIcon As Long
hCursor As Long
hbrBackground As Long
lpszMenuName As String
lpszClassName As String
End Type

Public Type POINTAPI
x As Long
y As Long
End Type

Public Type Msg
hwnd As Long
message As Long
wParam As Long
lParam As Long
time As Long
pt As POINTAPI
End Type
Public Const CS_VREDRAW = &H1
Public Const CS_HREDRAW = &H2
Public Const CW_USEDEFAULT = &H80000000
Public Const ES_MULTILINE = &H4&
Public Const WS_BORDER = &H800000
Public Const WS_CHILD = &H40000000
Public Const WS_OVERLAPPED = &H0&
Public Const WS_CAPTION = &HC00000 ' WS_BORDER Or WS_DLGFRAME
Public Const WS_SYSMENU = &H80000
Public Const WS_THICKFRAME = &H40000
Public Const WS_MINIMIZEBOX = &H20000
Public Const WS_MAXIMIZEBOX = &H10000
Public Const WS_OVERLAPPEDWINDOW = (WS_OVERLAPPED Or WS_CAPTION Or WS_SYSMENU Or WS_THICKFRAME Or WS_MINIMIZEBOX Or WS_MAXIMIZEBOX)
Public Const WS_EX_CLIENTEDGE = &H200&
Public Const COLOR_WINDOW = 5
Public Const WM_DESTROY = &H2
Public Const WM_LBUTTONDOWN = &H201
Public Const WM_LBUTTONUP = &H202
Public Const IDC_ARROW = 32512&
Public Const IDI_APPLICATION = 32512&
Public Const GWL_WNDPROC = (-4)
Public Const SW_SHOWNORMAL = 1
Public Const MB_OK = &H0&
Public Const MB_ICONEXCLAMATION = &H30&

声明几个我们需要的变量、常量：
Public Const gClassName = "MyClassName"
Public Const gAppName = "My Window Caption"
Public gButOldProc As Long
Public gHwnd As Long, gButtonHwnd As Long, gEditHwnd As Long

入口函数：
Sub Main
代码如下：
Public Sub Main()
Dim wMsg As Msg
''Call procedure to register window classname. If false, then exit.
If RegisterWindowClass = False Then Exit Sub

''Create window
If CreateWindows Then
''Loop will exit when WM_QUIT is sent to the window.
Do While GetMessage(wMsg, 0&, 0&, 0&)
''TranslateMessage takes keyboard messages and converts
''them to WM_CHAR for easier processing.
Call TranslateMessage(wMsg)
''Dispatchmessage calls the default window procedure
''to process the window message. (WndProc)
Call DispatchMessage(wMsg)
Loop
End If
Call UnregisterClass(gClassName$, App.hInstance)

End Sub
Public Function RegisterWindowClass() As Boolean
Dim wc As WNDCLASS

wc.style = CS_HREDRAW Or CS_VREDRAW
wc.lpfnwndproc = GetAddress(AddressOf WndProc) ''Address in memory of default window procedure.
wc.hInstance = App.hInstance
wc.hIcon = LoadIcon(0&, IDI_APPLICATION) ''Default application icon
wc.hCursor = LoadCursor(0&, IDC_ARROW) ''Default arrow
wc.hbrBackground = COLOR_WINDOW ''Default a color for window.
wc.lpszClassName = gClassName$
RegisterWindowClass = RegisterClass(wc) <> 0

End Function
Public Function CreateWindows() As Boolean

''开始创建窗体
主窗体.
gHwnd& = CreateWindowEx(0&, gClassName$, gAppName$, WS_OVERLAPPEDWINDOW, CW_USEDEFAULT, CW_USEDEFAULT, 208, 150, 0&, 0&, App.hInstance, ByVal 0&)
''创建一个按钮
gButtonHwnd& = CreateWindowEx(0&, "Button", "Click Here", WS_CHILD, 58, 90, 85, 25, gHwnd&, 0&, App.hInstance, 0&)
''创建一个(WS_EX_CLIENTEDGE、ES_MULTILINE风格的TextBox
gEditHwnd& = CreateWindowEx(WS_EX_CLIENTEDGE, "Edit", "This is the edit control." & vbCrLf & "As you can see, it's multiline.", WS_CHILD Or ES_MULTILINE, 0&, 0&, 200, 80, gHwnd&, 0&, App.hInstance, 0&)
"Button ","Edit"系统中已经注册过了所以这里直接用
创建完别忘了显示出来否则是隐藏的
Call ShowWindow(gHwnd&, SW_SHOWNORMAL)
Call ShowWindow(gButtonHwnd&, SW_SHOWNORMAL)
Call ShowWindow(gEditHwnd&, SW_SHOWNORMAL)
记下按钮处理过错的当前所在地址
gButOldProc& = GetWindowLong(gButtonHwnd&, GWL_WNDPROC)

''Set default window procedure of button to ButtonWndProc. Different
''settings of windows is listed in the MSDN Library. We are using GWL_WNDPROC
''to set the address of the window procedure.
指向新的处理过程地址
Call SetWindowLong(gButtonHwnd&, GWL_WNDPROC, GetAddress(AddressOf ButtonWndProc))
CreateWindows = (gHwnd& <> 0)

End Function
'窗体运行的主函数，在注册这个窗体时已经指定的
Public Function WndProc(ByVal hwnd As Long, ByVal uMsg As Long, ByVal wParam As Long, ByVal lParam As Long) As Long
Dim strTemp As String
处理消息，这里指处理了WM_DESTROY消息
Select Case uMsg&
Case WM_DESTROY:
''Since DefWindowProc doesn't automatically call
''PostQuitMessage (WM_QUIT). We need to do it ourselves.
''You can use DestroyWindow to get rid of the window manually.
Call PostQuitMessage(0&)
End Select

''Let windows call the default window procedure since we're done.
WndProc = DefWindowProc(hwnd&, uMsg&, wParam&, lParam&)
End Function
又添加了一个Button的处理过程
Public Function ButtonWndProc(ByVal hwnd As Long, ByVal uMsg As Long, ByVal wParam As Long, ByVal lParam As Long) As Long
Select Case uMsg&
Case WM_LBUTTONUP:
Call MessageBox(gHwnd&, "You clicked the button!", App.Title, MB_OK Or MB_ICONEXCLAMATION)
End Select

ButtonWndProc = CallWindowProc(gButOldProc&, hwnd&, uMsg&, wParam&, lParam&)

End Function

Public Function GetAddress(ByVal lngAddr As Long) As Long
GetAddress = lngAddr&
End Function
以上一个完整的简单的应用程序就产生了。我们不需要IDE环境也可以创建我们想要的风格的窗体。通过这个例子对于VB程序员是不是对系统的机制有了一些了解。
虽然这个例子实际意义并不大，但是我们认为很有用，让我们能了解一些封装背后隐藏的事实，使我们的思路很自由。
最后要声明这个想法并不是我一人想出来的，我参考一段代码（具体出处不祥）说想到，想与VB程序员共同分享一下，其实只要用活VB并没有我们所说的那么多限制，关键在使用者能否跳出这个范畴。