UnHook子类的安全方法(Unhook Subclassing When Windows is Ready)

Unhook Subclassing When Windows is Ready

Don’t unhook your Windows procedures from Form_Unload when
subclassing forms. When you subclass forms, the hook is often set
during Form_Load with code like this:
    OriginalProc = SetWindowLong Me.hWnd, _
                   GWL_WNDPROC, AddressOf MyWindowProc

A common mistake is forgetting to put the corresponding unhook
call in your Form_Unload event:(很容易忘了在Form_Unload 事件写如下代码)

      SetWindowLong Me.hWnd, GWL_WNDPROC, _
              AddressOf OriginalProc

If you forget to reinstate the old procedure in your Form_Unload
event, it’s bye-bye VB. Instead, add this code within your

subclassing procedure:(其实可以在安装子类时就写上如下窗口过程代码,就可以了，而且不怕进入调试模式!!!!)
Select Case Msg
Case WM_NCDESTROY
    If OriginalProc <> 0 Then
         Call SetWindowLong(hWnd, _
            GWL_WNDPROC, OriginalProc)
        OriginalProc=0
    End If
Case ...

This code restores the original procedure automatically when the
window is destroyed. To make it even safer, place all your
subclassing code in a separate DLL and debug your subclassed
forms without worrying about the Integrated Development Environment
(IDE) crashing. You can always move the code back to
your EXE when it’s fully debugged.