How to Use PostMessage() with FOXTOOLS

• Microsoft Visual FoxPro for Windows, version 3.0
• Microsoft FoxPro Library Construction Kit, version 2.5
• Microsoft FoxPro for Windows, versions 2.5, 2.5a, 2.5b

SUMMARY

The code example below demonstrates how FOXTOOLS.FLL can be used to call the PostMessage() function from FoxPro for Windows.

NOTE: For backward compatibility, Visual FoxPro still supports FOXTOOLS.FLL (included in earlier FoxPro versions), the Visual FoxPro API library that allows calls to 16-bit .DLL functions. However, in Visual FoxPro, the DECLARE command is the preferred method for calling .DLL functions.

MORE INFORMATION

The FOXTOOLS.FLL file is a FoxPro application programming interface (API) library that allows FoxPro programs to call many Windows dynamic-link library (DLL) functions. The FOXTOOLS.WRI document explains how to use FOXTOOLS.FLL. Both files are located in the GOODIES\FOXTOOLS subdirectory of the main FoxPro for Windows directory.

The PostMessage() function posts (places) a message in a window's message queue and then returns without waiting for the corresponding window to process the message. This function is part of the Microsoft Windows API. This function accepts the following parameters:

   BOOL PostMessage(hwnd, uMsg, wParam, lParam)

   HWND hwnd;     /* handle of the destination window */
   UINT uMsg;     /* message to post */
   WPARAM wParam;     /* first message parameter */
   LPARAM lParam;     /* second message parameter */

By using the PostMessage() function to send this message to the FoxPro window, you can "trick" FoxPro for Windows into thinking that the user chose Maximize from the Control menu.

Both WM_SYSCOMMAND and SC_MAXIMIZE are constants. These constants are defined in the WINDOWS.H file, which is included with the Windows Software Development Kit (SDK). By finding the location in WINDOWS.H where WM_SYSCOMMAND and SC_MAXIMIZE are defined, you can to determine that WM_SYSCOMMAND has a hexadecimal value of "0x0112" and SC_MAXIMIZE has a hexadecimal value of "0xF030". These hexadecimal values can be converted to decimal values of 274 and 61,488 respectively.

   * Load the FOXTOOLS library

   SET LIBRARY TO SYS(2004)+"FOXTOOLS.FLL"

   * Call RegFn() to register the PostMessage() function.

   func_ref = regfn("PostMessage", "IIIL", "I")

   * If RegFn() returned a value that is greater than -1, it
   * can be assumed that the function was successfully
   * registered.

   IF func_ref > -1

        * The mainhwnd() function, found in FOXTOOLS, is used to
        * obtain a handle for the main FoxPro window.

        wnd_hndl = mainhwnd()

        * CallFn() is used to call the PostMessage() function with
        * the appropriate parameters. The parameters required
        * by PostMessage() are found in the Windows Software
        * Development Kit. This particular call will place
        * a Maximize (274,61488) message in the message queue
        * for the FoxPro window (wnd_hndl). FoxPro will
        * respond by maximizing its main window.

        = callfn(func_ref,wnd_hndl,274,61488,0)

   ENDIF

   * Unload the library

   SET LIBRARY TO

REFERENCES

Microsoft FoxPro for Windows FOXTOOLS.WRI document Microsoft Windows Software Development Kit Microsoft Visual C++