SAMPLE: Appending Menu Items to Other Applications

• Microsoft Windows Software Development Kit (SDK) for Windows versions 3.0 and 3.1

SUMMARY

To enhance the functionality of an existing Windows-based application, new menu items can be added to the target application. The source application that adds the new menu items can also respond to these menu items when they are selected by a user. This article discusses the development of such a source application and the pitfalls associated with using this type of application.

There is sample code in the Software Library, in a file called SUBAPP, that demonstrates the feature of adding menu items to another Windows-based application.

Download SUBAPP.EXE, a self-extracting file, from the Microsoft Software Library (MSL) on the following services:

• Microsoft Download Service (MSDL)

        Dial (206) 936-6735 to connect to MSDL
        Download SUBAPP.EXE (size: 18261 bytes) 
  

• Internet (anonymous FTP)

        ftp ftp.microsoft.com
        Change to the \SOFTLIB\MSLFILES directory
        Get SUBAPP.EXE (size: 18261 bytes) 
  

MORE INFORMATION

To monitor the menu items of another application, the main window of that application is subclassed using the SetWindowLong() function. In the new window function, WM_SYSCOMMAND messages should be processed to handle the system menu items. If the menu items belong to a pop-up menu, WM_COMMAND should be processed. All the other messages and unrelated menu messages should be passed to the previous window function to maintain the integrity of the target application.

After subclassing the target application, new menu items or new pop-up menus can be added to it. To add menu items to the system menu or an existing pop-up menu, AppendMenu() is called, and to add new pop-up menus, InsertMenu() is called.

To make this process work in all three modes of Windows, a fixed code dynamic-link library (DLL) should be used. The DLL should contain the function that adds menu items and the new window function for the target application. This is because the code associated with such a mechanism must be available at all times. Certain EMS (expanded memory specification) memory configurations place all code except fixed library code segments in application-specific EMS memory. This makes the code availability limited to the application that owns the EMS memory. If that code is not available to the target application, it will crash under those EMS configurations.

NOTE: For future compatibility, the subclass procedure must be in a DLL for all modes.

Care should be taken when assigning ID (identification) values to the new menu items. The new ID values should not conflict with the values of the existing menu items; otherwise, the old menu items will be disabled. To determine the existing ID values of the target application, use SPY.EXE (included with the Windows SDK) to monitor WM_MENUSELECT messages when selecting menu items. The wParam parameter of WM_MENUSELECT message contains the ID value of the menu item selected.

Some applications, such as Microsoft Excel and Microsoft Word for Windows, use more than one menu; that is, each application has an option to use a long menu or a short one. These applications also allow their users to customize the menus. These features could become a problem when subclassing this type of application and monitoring new pop-up menus or new menu items.

For example, when subclassing Word for Windows, a new menu item is added under the pop-up menu "Utility". Suppose that, when appending the new item, the long version of the menu was selected. Later on, if the user changes to the short version of the menu, the new added menu item will be lost because Word for Windows would load the short version of its menus. To avoid this problem, add menu items to the system menu of Word for Windows -- changing the menu version does not effect the system menu.

Microsoft Excel and Microsoft Word for Windows can also display the menu items selected in a status window at the bottom. For this purpose, these applications use the WM_MENUSELECT message. If these applications receive a WM_MENUSELECT for a menu item that was not originally a part of their menu, they could crash when they refresh the status window. For this reason, in the new window function, WM_MENUSELECT messages related to all the new menu items should not be passed to the target application's old window function.

If there are a lot of new menu items to be added to an application, cascading menus should be used. Such a menu structure can help minimize the number of commands on an original pop-up menu of the target application.

As previously stated, there is a sample in the Software Library called SUBAPP that demonstrates the feature of adding menu items to another Windows-based application. In WinMain of SUBAPP.EXE, FindWindow() is called to get the handle of the desired application. If the application is present in the system, its main-window is subclassed with a new function and two new menu items are appended to its system menu. The new function monitors the messages of the target application. If any of those messages relate to the newly added menu items, the messages are handled accordingly; otherwise, they are sent to the target application's original function.

If, on the other hand, the application is not present, a message hook is installed to monitor the execution of the desired application. The message hook waits for the WM_PAINT message to arrive for the desired window class.

Upon receiving a WM_PAINT for the desired application, the callback hook function subclasses the other application and appends menu items to its system menu. The hook function then posts a message to the calling application (SUBAPP.EXE) to unhook the message filter, since there is no longer a need for a system message hook.

If the other application quits before the termination of SUBAPP.EXE, a message hook is set that again waits for the activation of the desired application to append the menu items. If SUBAPP.EXE is closed before the target application, the added menu items are removed and the application is no longer subclassed.

The message hook, the subclassing function for the application, and all of the menu appending and removing calls are placed in a fixed code DLL, called LIBSUBAP.DLL. This guarantees that SUBAPP.EXE will work properly in all of the three modes of Windows.

SUBAPP.EXE can be used to subclass any Windows-based application as long as the class name of the target application's main window is known. In the application's header file (SUBAPP.H), the constant OTHER_CLASS_NAME can be initialized to the desired application's main-window class name.