An additional framework to support DSM
was made to handle application start, exit, and navigation.
In addition to basic start and exit code, this domain framework included a
dispatcher that started the application by calling the ?¬?rst function and looping until the
application exit was reached. This code was generated as part of the main function of
the application code, as already shown in detail with the application code in
Listing 8.5. A bigger part of the framework code was made to handle the navigation
stack, which enables getting back to the previously accessed function without starting
a new one. Here, basic stack handling operations were designed so that application
objects (functions in generated code) that could be targets for cancel navigation are
pushed onto the stack after accessing the next element in the ?¬‚ow. Correspondingly,
they are popped from the stack when they are the target of a cancel. Not all concepts in
the navigation ?¬‚ow were put on the stack as they were not suitable for canceling. For
example, a canceling operation that would trigger an already closed stand-alone
application outside the Python application scope would not make sense.
The last piece of the framework code was made to take care of concurrency control
in the UI application code. Python for S60 requires that execution paths be blocked
when certain phone services are used: the concept of an active object in the underlying
Symbian OS needs to be recognized.
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