Check if widget exists on desktop using appWidgetId

Question

I use AlarmManager to update my widgets. And I want to stop it if there is no widget on the desktop. But I had a problem with detecting the absence of a widget on the main screen.

As always, when I try to use AppWidgetId using this method:

 AppWidgetManager appWidgetManager = AppWidgetManager.getInstance(context); int[] appWidgetIDs = appWidgetManager .getAppWidgetIds(new ComponentName(context, Widget.class)); 

I get the length of appWidgetIDs while there is no widget on the main screen. Why?

So I would like to know if there is a way to detect that there is a widget id on the home screen.

Thanks in advance.

Answer 1

Congratulations, you are facing phantom appwidgets. It appears to be documented in tracking Android issues . Usually they occur when the configuration activity for the application is visibly canceled, although this seems to be due to the incorrect implementation of the configuration activity; developers neglect to add the appwidget identifier as an additional identifier when setting the result of an operation to RESULT_CANCELED . (even the Google ApiDemos sample application neglects this!)

The correct implementation is as follows:

 public class AppWidgetConfigActivity extends Activity { private int appWidgetId; private Intent resultValue; protected void onCreate(bundle saved) { super.onCreate(saved); // get the appwidget id from the intent Intent intent = getIntent(); appWidgetId = intent.getIntExtra(AppWidgetManager.EXTRA_APPWIDGET_ID, AppWidgetManager.INVALID_APPWIDGET_ID); // make the result intent and set the result to canceled resultValue = new Intent(); resultValue.putExtra(AppWidgetManager.EXTRA_APPWIDGET_ID, appWidgetId); setResult(RESULT_CANCELED, resultValue); // if we weren't started properly, finish here if (appwidgetId == AppWidgetManager.INVALID_APPWIDGET_ID) { finish(); } /* ... */ } /* ... */ private void finishConfigure() { /* finish configuring appwidget ... */ setResult(RESULT_OK, resultValue); } } 

So far, I do not know how to detect the presence of a phantom appwidget without your own accounting statements. I suggest storing a SharedPreferences value indicating that the configuration activity has not been canceled, and then request that value in your other code. You can also use this information to “uninstall” the phantom widget if you encounter it. In your appwidget configuration configuration:

 private void finishConfigure() { /* finish configuring appwidget ... */ setResult(RESULT_OK, resultValue); String key = String.format("appwidget%d_configured", appwidgetId); SharedPreferences prefs = getSharedPreferences("widget_prefs", 0); prefs.edit().putBoolean(key, true).commit; } 

You can then verify that you have at least one non-w603 appwidget:

 AppWidgetManager appWidgetManager = AppWidgetManager.getInstance(context); AppWidgetHost appWidgetHost = new AppWidgetHost(context, 1); // for removing phantoms SharedPreferences prefs = getSharedPreferences("widget_prefs", 0); boolean hasWidget = false; int[] appWidgetIDs = appWidgetManager.getAppWidgetIds(new ComponentName(context, Widget.class)); for (int i = 0; i < appWidgetIDs.length; i++) { int id = appWidgetIDs[i]; String key = String.format("appwidget%d_configured", id); if (prefs.getBoolean(key, false)) { hasWidget = true; } else { // delete the phantom appwidget appWidgetHost.deleteAppWidgetId(id); } } if (hasWidget) { // proceed } else { // turn off alarms }