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5
Application Management
AMS, MIDlet
pauseApp()
AMS
destroyApp()
MIDlet
notifyDestroy
ed()
On a device without a windowing system, only one application can have focus at a time.
When an application has focus, it receives keypad input, and has access to the display,
speakers, LED lights, vibrator, etc. The C370, C450, and C550 device can only run one
MIDlet at a time, but that MIDlet has to share focus with the system user interface. That
user interface is a higher priority than the MIDlet, so the MIDlet will immediately lose focus
when the system needs to handle a phone call or some other interrupt.
The concept of focus correlates directly with the MIDlet state. i.e. when a MIDlet loses
focus because of a phone call, the MIDlet is immediately paused. Conversely to the
example of starting the MIDlet, the MIDlet loses focus immediately, then its
pauseApp() method is called.
The paused state is not clearly defined by MIDP. The only requirement placed on the
device manufacturer is that a paused MIDlet must be able to respond to network events
and timer events. On Motorola devices, the paused state simply implies that the MIDlet is
in the background as mentioned above, but it doesn't force any of the threads to stop
execution. Essentially, a paused MIDlet is a MIDlet without focus whose pauseApp()
method has been called. It's up to the developer to control their threads, such as making
them sleep for longer periods, completely pausing game threads, or terminating threads
that can be restarted when the MIDlet is made active again.
Similarly, a MIDlet's focus is also lost immediately before its destroyApp() method
is called.
The MIDlet must be written properly (as described above) to implement all methods in the
javax.microedition.midlet package, especially startApp( ) and pauseApp( ). A
The pauseApp() method is called from either AMS or
from within the MIDlet.
The pauseApp() should pause active threads, and
prepare for startApp() to be called.
If the application is to be resumed with a screen other than
the present, then the Displayable should be set current in
the startApp() or the pauseApp().
The destroyApp() method is called from AMS and
signals the MIDlet to clean up any resources to prepare for
termination. For example, open RMS records should be
closed, threads should be stopped, and any other
housekeeping chores should be performed.
The MIDlet should not call destroyApp().
The notifyDestroyed() method is called by the
MIDlet to exit and terminate itself.
All housekeeping such as stopping active threads and
closing RMS records should be performed before calling
notifyDestroyed().
notifyDestroyed() notifies AMS to terminate the
calling MIDlet.
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