Книга: Microsoft Windows Embedded CE 6.0 Exam Preparation Kit

Implementing Control Panel Applets

Implementing Control Panel Applets

As mentioned, a Control Panel applet is a configuration tool for a system component or user application implemented in form of a .cpl file and located in the Windows folder on the target device. Essentially, a .cpl file is a DLL that implements the CPlApplet API. A single .cpl file can contain multiple Control Panel applications, yet a single applet cannot span multiple .cpl files. Because all .cpl files implement the CPlApplet API, it is a straightforward process for Control.exe to obtain detailed info about the implemented applets at startup in order to display the set of available applets in the user interface. Control.exe only needs to enumerate all .cpl files in the Windows folder and to call the CPlApplet function in each file.

According to the DLL nature and CPlApplet API requirements, .cpl files must implement the following two public entry points:

? BOOL APIENTRY DllMain(HANDLE hModule, DWORD ul_reason_for_call, LPVOID lpReserved) Used to initialize the DLL. The system calls DllMain to load the DLL. The DLL returns true if initialization succeeded or false if initialization failed.

? LONG CALLBACK CPlApplet(HWND hwndCPL, UINT message, LPARAM lParam1, LPARAM lParam2) A callback function that serves as the entry point for the Control Panel to perform actions on the applet.

The Control Panel calls the CPlApplet function to initialize the applet, obtain information, provide information about user actions, and to unload the applet. The applet must support several Control Panel messages, listed in Table 3-6, to implement a fully functional CPlApplet interface:

Table 3-6 Control Panel messages

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