Question

I will make it simple. I have my widget code. My widget layout contains a linear layout with one button in it. In my widget code, I initialize a String List with some values in it.
When I click the button in my widget, I have to update my List with some more values.

So, this is my code,

List<String> myList = null;
public void onUpdate(Context context, AppWidgetManager appWidgetManager,
        int[] appWidgetIds) {
myList = new List<String>();
myList.add("1");
myList.add("2");
...
Intent intent = new Intent(context, getClass());
intent.setAction("CALL_UPDATE");
PendingIntent pendingIntent = PendingIntent.getBroadcast(context, 0, intent, 0);
views.setOnClickPendingIntent(R.id.button, pendingIntent);
....
}

@Override
public void onReceive(Context context, Intent intent) {
    if (intent.getAction().equals("CALL_UPDATE")) {
        Toast.makeText(context, "Intent received"+myList , 2000).show();
    }
}

When the button is clicked, the broadcast is properly received by onReceive(). The problem is, on onReceive(), I see my list as null instead of some values in it as some string objects were added earlier.

Can anyone help?

Thx!
Rahul.

Answer 1

Documentation says:

This has important repercussions to what you can do in an
onReceive(Context, Intent) implementation: anything that requires
asynchronous operation is not available, because you will need to
return from the function to handle the asynchronous operation, but at
that point the BroadcastReceiver is no longer active and thus the
system is free to kill its process before the asynchronous operation
completes.

In particular, you may not show a dialog or bind to a service from
within a BroadcastReceiver. For the former, you should instead use the
NotificationManager API. For the latter, you can use
Context.startService() to send a command to the service.

And:

onReceive() is normally called within the main thread of its process,
so you should never perform long-running operations in it (there is a
timeout of 10 seconds that the system allows before considering the
receiver to be blocked and a candidate to be killed). You cannot
launch a popup dialog in your implementation of onReceive().

Edit:
AppWidgetProvider is a BroadcastReceiver and it’s instance (and so it’s fields) will be deleted after it’s lifcycle.When you create a new instance of widget in HomeScreen,onUpdate and onReceive of AppWidgetProvider invoke and list of this instance of AppWidgetProvider is not null.But after invoking onReceive (for example 10 seconds)this instance will delete.When you click on button ,second instance of AppWidgetProvider will be create and it’s list is null.
You can save your list public static field of a class and retrieve it when you need.