Update android widget on condition

Question

I'm just starting with android development and have written an application to show details about the battery status. Now I wanted to put the whole thing into an widget - and here's the question: Do I really need a update service in the background to listen for ACTION_BATTERY_CHANGED intents? My first thought was to put just a line into the intet-filter tag of the widget in the AndroidManifest.xml - but obviously it's not that simple. If the UpdateService is the right way I'll do so - but I just wanted to make sure what the proper solution is

Answer 1

Do I really need a update service in the background to listen for ACTION_BATTERY_CHANGED intents?

You cannot use a manifest-registered BroadcastReceiver for ACTION_BATTERY_CHANGED. It can only be registered by an activity or service via registerReceiver().

If you do not have a service in memory for other reasons, a better approach is to poll. Set up an AlarmManager to check the battery level every so often (configurable, please!). To check the battery level, call registerReceiver() for an ACTION_BATTERY_CHANGED IntentFilter without a BroadcastReceiver (null for the first parameter). This will return the last-broadcast ACTION_BATTERY_CHANGED Intent, from which you can get the most-recent charge level.

Answer 2

I suggest you poll the battery status periodically, e.g. every 30 min. To do that you can simply specify a value for updatePeriodMillis in your AppWidgetProviderInfo

<appwidget-provider
   xmlns:android="http://schemas.android.com/apk/res/android"
   android:updatePeriodMillis="1800000" />

..and update your widget by overriding the onUpdate method of your AppWidgetProvider.

edit: As pointed out by Martin, 30 min is actually the shortest interval in which you can receive updates this way.

Answer 3

Believe it or not, the following works:

cont.getApplicationContext().registerReceiver(rec, filter);