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

I found this under a project named 24clock in goole code. It try Not update the widget while user is away from home:

    ActivityManager am = (ActivityManager)getSystemService(Context.ACTIVITY_SERVICE);

    List<RunningTaskInfo> runningTasks = am.getRunningTasks(2);
    for (RunningTaskInfo t : runningTasks) {
        if (t != null && t.numRunning > 0) {
            ComponentName cn = t.baseActivity;
            if (cn == null) continue;

            String clz = cn.getClassName();
            String pkg = cn.getPackageName();

            // TODO make this configurable
            if (pkg != null && pkg.startsWith("com.android.launcher")) {
                return true;
            }

            return false;
        }
    }

It might be an answer for you requirement #2. Although it might not work under other 3rd party launchers.