A Task Tray Applet Framework

When I implemented CJBControlPanelApplet I placed multiple applets in a single DLL. After writing much of the same "base class has a static list" code again for the task tray applet I decided to try and create a common base class that incorporated and hid all of the "I'm a class whos instances are in a static list" functionality. It seemed simple enough until I realised that to be type-safe and remove heaps of casts in the derived class the base class needed to know about the derived class. Without a second thought I templatised the base class and had the derived class inherit from it thus:

class CTaskBarApplet : public CLinkedClass<CTaskBarApplet>

Then I thought about it and it seemed like a really odd thing to do. It worked great and gave no warnings but was it nice? Since then I've spoken to several people and read Stroustrup 3e (and he thinks it's a "Good Thing") and now I like the idea. It did seem very odd at first though...

Once I had a standard way to link instances of a class together I needed a way to navigate this list at run-time. After several aborted attempts I ended up with an STL-style iterator. This lets you do things like:

for (Iterator addIt = Begin(); addIt != End(); addIt++)
{
   addIt->AddIcon();   // call any derived class method here
}

Of course, having moved the common functionality out into a base class I never got around to using the base class in CJBControlPanelApplet, but I've used it in plenty of other places.

The CPlTrayApplet and CPlAppletClient classes

By this stage I had a task tray framework but I still needed to somehow reuse the code in my control panel applet. Since a .cpl is just a DLL, and since I'd worked out how CPlApplets worked when I wrote CJBControlPanelApplet I decided to write a wrapper class that could load a control panel applet, send it all the right messages to initialise it and then run the applet. Once I had CJBCPlAppletClient I derived a CJBCPlTrayApplet from CJBTaskTrayApplet and wired the two together. The end result was a collaboration something like this:

CJBCPlAppletClient isn't linked in any way to the task tray classes. It's just used by CJBCPlTrayApplet . It can be used anywhere you want to access a control panel applet programmatically.

Using MFC with the framework

When I started looking at task tray applets I tried to write one with MFC. I've seen it done but you have to do a fair bit of work to get it to work right. Message map entries for the callback message, preventing the CWinApp's main window from popping up briefly, etc, etc. I didn't need MFC so I wrote the straight Win32 solution. Then I wanted a single complex dialog in a task tray applet and I wanted to use MFC for the dialog and my framework for the applet... It all went well until I ran it and the dialog died with assertion failures, I didn't have a CWinApp derived class and it was a serious requirement... Since I didn't have time to convert my applet framework to a CWinApp derived framework I cheated. Since all that is required is that a CWinApp object exists so that the dialog has a message pump to use I stuck a vanilla CWinApp object inside WinMain and called AfxWinInit() directly and everything worked fine... An #ifdef around this version of WinMain() means that at the flick of a #define you can have either MFC enabled or lean and mean versions of your task tray applets.

I really keep meaning to sit down and make CJBTaskTrayApplet a real CWinApp derivative, but, this works...

See article on Len's homepage for the latest updates.