CWAC Wakeful: Staying Awake At Work
The recommended pattern for Android's equivalent to cron
jobs and Windows scheduled tasks is to use
This works well when coupled with an
IntentService, as the
service will do its work on a background thread and shut down
when there is no more work to do.
There's one small problem:
IntentService does nothing to keep
the device awake. If the alarm was a
WAKEUP variant, the phone
will only stay awake on its own while the
handling the alarm is in its
onReceive() method. Otherwise,
the phone may fall back asleep.
WakefulIntentService attempts to combat this by combining
the ease of
IntentService with a partial
This is available as a JAR file from the downloads area of this GitHub repo. The project itself is set up as an Android library project, in case you wish to use the source code in that fashion.
WakefulIntentService v0.4.0 and newer requires Android 2.0+, so it
can take advantage of
onStartCommand() for better handling of
crashed services. Use earlier versions of
you wish to try to use it on older versions of Android, though this
is not supported.
Any component that wants to send work to a
WakefulIntentService subclass needs to call either:
MyService.class is the
intentOfWork is an
Intent that will be used to call
startService() on your
WakefulIntentService must override
doWakefulWork() instead of
will be processed within the bounds of a
the semantics of
doWakefulWork() are identical to
doWakefulWork() will be passed the
Intent supplied to
sendWakefulWork() (or an
Intent created by the
method, depending on which flavor of that method you use).
And that's it.
WakefulIntentService handles the rest.
NOTE: this only works with local services. You have no means
of accessing the static
WakeLock of a remote service.
NOTE #2: Your application must hold the
NOTE #3: If you get an "
WakeLock under-locked" exception, make sure
that you are not starting your service by some means other than
If you want to slightly simplify your use of
in conjunction with
AlarmManager, you can do the following:
First, implement your
as described above.
Next, create a class implementing the
interface. This class needs to have a no-argument public constructor
in addition to the interface method implementations. One method
scheduleAlarms(), where you are passed in an
PendingIntent, and a
Context, and your mission is to schedule
your alarms using the supplied
PendingIntent. You also implement
sendWakefulWork(), which is passed a
Context, and is where
sendWakefulWork() upon your
implementation. And, you need to implement
should return the time in milliseconds after which, if we have
not seen an alarm go off, we should assume that the alarms were
canceled (e.g., application was force-stopped by the user), and
should reschedule them.
Then, create an XML metadata file where you identify the class
WakefulIntentService.AlarmListener from the
previous step, akin to:
<WakefulIntentService listener="com.commonsware.cwac.wakeful.demo.AppListener" />
<receiver> in your manifest, set to respond to
ACTION_BOOT_COMPLETED broadcasts, and with a
<meta-data> element pointing to the XML resource from
the previous step, akin to:
<receiver android:name="com.commonsware.cwac.wakeful.AlarmReceiver"> <intent-filter> <action android:name="android.intent.action.BOOT_COMPLETED"/> </intent-filter> <meta-data android:name="com.commonsware.cwac.wakeful" android:resource="@xml/wakeful"/> </receiver>
Also, add the
RECEIVE_BOOT_COMPLETED permission to your manifest.
Finally, when you wish to manually set up the alarms (e.g., on
first run of your app), create an instance of your
scheduleAlarms() on the
class, passing in the
AlarmListener and a
the activity that is trying to set up the alarms).
Over time, this portion of the framework will be expanded further to help consolidate a good usage pattern for managing alarms.
Additional documentation can be found in the "AlarmManager: Making the Services Run On Time" section of this free excerpt from The Busy Coder's Guide to Advanced Android Development.
This is version v0.5.1 of this module, meaning it is proving to be surprisingly popular.
demo/ project directory and
com.commonsware.cwac.wakeful.demo package you will find
AppListener, which is an implementation of
AppService pretends to do some work in a background
thread. All of this is set up via a
to move the application out of the "stopped" state on Android 3.1+),
and if needed on a reboot.
Note that when you build the JAR via
ant jar, the sample
activity is not included, nor any resources -- only the
compiled classes for the actual library are put into the JAR.
The code in this project is licensed under the Apache Software License 2.0, per the terms of the included LICENSE file.
If you have questions regarding the use of this code, please post a question
on StackOverflow tagged with
android. Be sure to indicate
what CWAC module you are having issues with, and be sure to include source code
and stack traces if you are encountering crashes.
- v0.5.1: semi-automatically handle canceled alarms (e.g., app force-stopped)
- v0.5.0: added the
AlarmListenerportion of the framework
- v0.4.5: completed switch to
- v0.4.4: switched to
- v0.4.3: added better recovery from an
- v0.4.2: added
volatilekeyword to static
WakeLockfor better double-checked locking implementation
- v0.4.1: added
setIntentRedelivery()call, nuked extraneous permissions check
- v0.4.0: switched to
onStartCommand(), requiring Android 2.0+ (API level 5 or higher)
- v0.3.0: converted to Android library project, added test for