Chapter 1

private: // from CEikDocument
CEikAppUi* CreateAppUiL();
};
Again, because the application is intended to run on a P800, I'm deriving from a UIQ class.
The implementation is as follows:
CHelloGuiDocument::CHelloGuiDocument(CEikApplication& aApp)
: CQikDocument(aApp)
{
}
CEikAppUi* CHelloGuiDocument::CreateAppUiL()
{
return new(ELeave) CHelloGuiAppUi;
}
We start with a C++ constructor that simply calls CQikDocument's constructor, passing in
the application as an argument. Next, there's the virtual CreateAppUiL() function which,
to nobody's surprise, returns a new app UI. An application that is not UI-specific would
simply replace the references to CQikDocument with ones to CEikDocument.
Note carefully that CreateAppUiL() is responsible only for first- phase construction (which
excludes any initialization that might fail). We'll see the second phase, to perform the
possibly failure-prone initialization, shortly.
The application UI
The GUI action proper starts with the app UI, which has two main roles:
� to get commands to the application,
� to distribute keystrokes to controls, including the application's main view, which is
owned by the app UI.
A command is simply an instruction without any parameters, or any information about where
it came from, which the program must execute. In any practical GUI program, you implement
HandleCommandL(TIntaCommandId) in your derived app UI class. The command ID is
simply a 32-bit integer.
The definition is deliberately vague, since commands can originate from a variety of places.
In UIQ applications, commands usually originate from an application's menu or – at least, in
the emulator – from a shortcut key. (Applications may assign a shortcut key to any command
ID – regardless of whether it is shown on the menus. The conventional shortcut key for the
Close command, for instance, is Ctrl+E.)
In other customized UIs, commands may originate from other sources. In the Series 80
(Crystal) UI application, for example, which shows commonly used commands on a toolbar,
commands may come from a toolbar button.
A command may be available from any or all of these sources. It doesn't matter where it
comes from, the app UI receives it as a 32-bit command ID in HandleCommandL() and
simply executes the appropriate code to handle the command.