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Visual Basic 6 definition

Declare Function DefWindowProc Lib "user32.dll" Alias "DefWindowProcA" (ByVal hWnd As Long, ByVal Msg As Long, ByVal wParam As Long, ByVal lParam As Long) As Long

Visual Basic .NET definition

Declare Function DefWindowProc Lib "user32" Alias "DefWindowProcA" (ByVal hwnd As Integer, ByVal wMsg As Integer, ByVal wParam As Integer, ByVal lParam As Integer) As Integer

C# definition

[DllImport("user32", EntryPoint="DefWindowProc")] public static extern int DefWindowProcA(int hwnd, int wMsg, int wParam, int lParam)

Description

DefWindowProc explicitly calls the operating system's default window procedure to process a message for a window. This default window procedure provides the minimal functionality necessary for a window procedure function and should be used to provide the default implementation of window messages. DefWindowProc Calls the default window procedure to provide default processing for any window messages that an application does not process. Any of the following:System.Windows.Forms.Form.DefWndProcSystem.Windows.Forms.Control.DefWndProcSystem.Windows.Forms.NativeWindow.DefWndProc

Return Value

The function returns the return value of whatever message was processed.

Parameters

hWnd A handle to the window to process a message for. Msg The message to process. wParam Additional information about the message. lParam Additional information about the message.

Further Information:

For further information on Windows API functions such as these, and how to use these API's in your C# and VB.NET applications, please refer to the book 'Network programming in .NET' (Buy at Amazon UK) (Buy at Amazon US)

Visual Basic 6 example source code
' Demonstrate how Visual Basic provides a more robust window ' procedure for windows it creates for the programmer when compared ' to Windows's default window procedure. Do this by "toggling" between ' the default and the Visual Basic provided one. ' *** Place the following code in a module. *** Public pVBProc As Long ' pointer to Visual Basic's window procedure ' (The above variable defaults to 0 automatically.) ' The following function acts as a wrapper. All it ' does is call the default window procedure. Public Function WindowProc (ByVal hWnd As Long, ByVal uMsg As Long, ByVal wParam As Long, ByVal lParam As Long) As Long ' Call the default window procedure and return its result. WindowProc = DefWindowProc(hWnd, uMsg, wParam, lParam) End Function ' *** Place the following code wherever you wish. *** Dim retval As Long ' return value If pVBProc = 0 Then ' Window Form1 is using the VB-provided procedure. Switch to using ' the default one and save the pointer to the VB one. pVBProc = SetWindowLong(Form1.hWnd, GWL_WNDPROC, AddressOf WindowProc) Else ' Window Form1 is using the default procedure (via the wrapper ' function). Switch to using the VB one. retval = SetWindowLong(Form1.hWnd, GWL_WNDPROC, pVBProc) ' Set pVBProc to 0 so we know which one is being used. pVBProc = 0 End If ' By allowing the user to switch back and forth, the differences will ' become apparent.
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