Introduction
Visual C++ revolves around messages. Messages are sent to controls
from windows giving them information and instructing them to do things. Messages
are also sent from controls to windows, and to other controls. Being able to
send messages to controls allows you to do much more than using Visual Basic
procedures. Messages can be sent using the SendMessage function in the user32.dll.
To use it, simply enter the following declaration into a form. If you want to
enter it into a module, and use it throughout the project, change the Private
to Public.
Private Declare Function SendMessage
Lib "user32" Alias "SendMessageA" (ByVal hwnd As Long, ByVal
wMsg As Long, ByVal wParam As Long, lParam As Any) As Long
All you need to know to send a message to a control is its hWnd
property and the command you want to send to it. To find the command you want
to use, load up the API Text Viewer, and select Constants from the API Type
list box. Constants that begin with WM_ tell the control to do something, EM_
to return a value.
The advantage of being able to send these commands is that you
are using the controls code, which you presume is bug free, rather than your
own. This will save space as well as time. Of course if you want to do something
the control can't do you have to write your own code still.