S60 devices are Symbian OS devices and support multitasks. When switching
a MIDlet to the background, audio stream playback does not stop. Developers
should implement stopping playback at the moment the MIDlet loses foreground.
With a low-level UI, such as Canvas and GameCanvas,
stopping playback can be implemented in the Canvas.hideNotify() method,
which is called just after the MIDlet loses the foreground. Restarting playback
can be implemented in the Canvas.showNotify() method,
which is called just before the MIDlet returns to the foreground. With a high-level
UI, such as List and Form, Displayable.isShown() can
be used to check whether the calling Displayable is actually
visible on the display. Developers can implement checking isShown() in
a proper frequency to stop or restart playback.