Chapter 1

eturn KErrNone;
}
Important
You must code the prototype of NewApplication() exactly as
shown, otherwise the C++ name mangling will be different from that
expected by the build tools' first ordinal export specification, and your
application won't link correctly.
My NewApplication() function returns my own application class, after first-phase
construction. In the rather unlikely event that there isn't enough memory to allocate and C++construct
a CHelloGuiApplication object, NewApplication() will return a null pointer
and the application architecture loader will handle cleanup.
Note in passing that all Symbian OS DLLs must also code an E32Dll()function that ought
to do nothing, as mine does above.
Note
If it exists to do nothing, why is the function there and why does it take a
parameter? In Windows terminology, this function is the DLL entry point, and
it's called when the DLL is attached to or detached from a process or thread
– at least, that's the theory, and we thought that would be useful for
allocating DLL-specific data in the early days of Symbian OS development.
The application
In practice, however, it isn't called symmetrically in Windows, so it doesn't
work under the emulator, and therefore, is pretty useless for Symbian OS
development. Furthermore, different versions of Symbian OS call E32Dll() a
differing number of times and in slightly different circumstances, which are
further reasons not to use this function to do any real work in your
application. Calls to this function are likely to be withdrawn in future versions
of Symbian OS.
If you need to allocate DLL-specific memory, use the thread- local storage
functions Dll::Tls() and Dll::SetTls(): call them from your main
class' C++ constructor and destructor, and point to your class rather than
some other ad hoc global variable structure. See Chapter 8 and
\release\generic\app-framework\cone\src\coemain.cpp (along with
\release\ generic\app-framework\cone\src\coetls.h) in the SDK for
an example.
Assuming that NewApplication() returned an application, the architecture then calls
AppDllUid() to provide another check on the identity of the application DLL. That's all it
needs to know about the application. It then calls CreateDocumentL(), which the
application uses to create a default document. Both of these are virtual functions that I
implement in my derived application class.
The definition of CHelloGuiApplication in HelloGui_Application.h is as follows:
class CHelloGuiApplication : public CQikApplication
{
private: // Inherited from class CApaApplication
CApaDocument* CreateDocumentL();
TUid AppDllUid() const;
};