Android - how update widget often but only when it is visible?

Question

I'm going to create widget which needs to update its content every minute (it shows time-related data).

However, there is no need to update widget if it is currently invisible, which means:

• screen is turned off
• another app is running
• widget is placed on another (invisible) home screen tab

What is the best way to update only visible widget every minute - without waking up device nor doing unnecessary computations? After widget becomes visible, small lag before update is acceptable.

Answer 1

To keep from updating when the screen is off, use the AlarmManager to schedule a recurring alarm that doesn't wakeup the phone.

The other two bullet points you have in your question aren't possible. There is no way to detect if your widget is on a home screen that isn't currently visible, and there is no way to determine if an app is running that is hiding the home screen. I have filed a ticket on http://b.android.com requesting this functionality be added to Android. If you feel like starring it, it will help it gain priority: http://code.google.com/p/android/issues/detail?id=5529&q=reporter:mark.r.baird&colspec=ID%20Type%20Status%20Owner%20Summary%20Stars

Answer 2

1. You can ask the PowerManager about isScreenOn()
2. You can register for Intent ACTION_SCREEN_OFF/ACTION_SCREEN_ON and turn you timer on/off accordingly.

Allthough the answer above concerning the AlarmManager is correct it may not be sufficient since I observed many phones also delivering alarms even if they are not of type *_WAKEUP. This may happen if there are other applications installed that are waking up the device. And if it is once awake, it delivers all pending alarms.