3
OS, arrays are handled by either the RArray classes or one of the classes inherited from these
base classes. Maps are handled by the
RHashMap and RHashSet classes, and lists are handled by
the
TSglQue class. Both platforms now support the Standard Template Library to provide a
common library of data structures.
A key problem when moving from the Windows environment to Symbian OS is the handling of
strings. The C API uses the Standard C library for handling strings (
string.h), and MFC uses its
own string class called
CString. Symbian OS, however, has its own hierarchy of string objects and
interfaces called descriptors. Descriptors are one of the most fundamental classes in Symbian OS
and emphasis needs to be placed on learning them in depth, especially how they are used in place
of
CString. Due to their complex, inheritance-based nature, a full description of these classes and
their usage is beyond the scope of this paper; there are additional links to descriptor tutorials in the
‘Technical Resources’ section.
It is standard to use a client-server model for interaction with system services on Symbian OS. This
allows for controlled access to the service. Normally in Symbian OS, a connection is made to a
service and the connection is used to create other objects based on that session. Whilst in MFC a
CFile object would be created, in Symbian OS this requires a connection to the file server (RFs)
and then a file object (
RFile) to be opened on the file server session.
2.3 Application Structure
Most native code developers on Windows Mobile will be familiar with the Windows message
architecture. In Windows, there is a main message loop that waits for a message and, when one is
received, dispatches it to the correct window via
GetMessage()/DispatchMessage() and a
WndProc() handler for each type of registered window. This allows for asynchronous and
synchronous processing using the
PostMessage() and SendMessage() functions.
The equivalent on Symbian OS uses the active object framework, with the active scheduler
performing the same role as the message pump.
2
The active scheduler waits for an active object to
be signaled and when this happens the active scheduler calls the
RunL() method of the
appropriate active object. It is important to note that the active object framework is, by definition,
non-pre-emptive and requires the developer to break long running tasks into a number of states,
otherwise the thread may become unresponsive whilst processing a request. This should be very
familiar to most Windows developers and the same rule applies during the processing in the
WndProc() function of the window class instance.
MFC provides for a full application framework, with a model/view/controller type framework for the
user interface. This translates easily on to the Symbian OS UIKON UI framework which has
classes that are very similar in design to the MFC classes. There is a document object, an
Application UI (frame window) object, view and container (
CWnd) support. The MFC framework
itself is responsible for routing commands in the framework; much like the Application UI does for
Symbian OS and its licensees’ derivatives.
A list of MFC classes with their corresponding Symbian C++ and S60 APIs is shown in Table 1.
2
Fibers on the Microsoft Windows platform is similar to active objects. However, unlike Symbian OS, the
scheduling of the fibers is left to the application developer.
