Chapter 1

Figure 4.4
After NewApplication(), you'll see all the other initialization functions in the application,
document, app UI, and app view classes called in the correct sequence. Eventually, you'll
see CHelloGuiAppView::\Draw() being called, and after that the emulator window is
displayed.
4.8 Command and Event Handling
When you look at the code for HandleCommandL(), you might not think it's worth
debugging – after all, it's just a simple switch statement, and all the case handlers are
one-liners. In fact, it's worthwhile for a number of reasons:
� There are several ways of getting commands to HandleCommandL(), and it's
informative to look at the call stack in the debugger to see how commands that come
from different starting points arrive in the same place.
� Most of the case handlers display an info-message, and when that disappears your
application view has to redraw itself. Because of this, your Draw() function gets called,
with some surprises that we'll return to in Chapter 11.
� Most calls to HandleCommandL() are generated as a result of some user-initiated
event (an exception for UIQ is a system-generated Exit command). As we saw in
Chapter 2, this means active objects are involved in handling them. We can easily
observe this by debugging through HandleCommandL().
� You begin to get a feel for many of the relationships between the window server,
controls, and your application. These relationships are the stuff of life for GUI
programming, and I'll be explaining them in later chapters.
In the next few sections, we'll invoke commands from the menu and shortcut keys, and I'll
point out some of the interesting things revealed by the debugger.
4.8.1 Pointer-generated Commands from the Menu Bar
Starting with the first of these, use the pointer to select and press a menu option, say Edit |
Item 2.
You'll see the debugger stop at the HandleCommandL() breakpoint, where the Variables
window reveals the value of the aCommand parameter to be 4098, or 0x1002, which is
EHelloGuiCmd2. The Call Stack window reveals what is happening:
CCoeEnv::RunL()