Get battery level before broadcast receiver responds for Intent.ACTION_BATTERY_CHANGED

Question

I have a broadcast receiver in my program to get react to the battery level like so:

private BroadcastReceiver mBatInfoReceiver = new BroadcastReceiver(){
    @Override
    public void onReceive(Context arg0, Intent intent) {
        int level = intent.getIntExtra("level", 0);
        // do something...
    }
}

    registerReceiver(this.mBatInfoReceiver, 
            new IntentFilter(Intent.ACTION_BATTERY_CHANGED));

However this code has to wait for the battery status to be updated so if you have a GUI element that needs to be set based on the battery level it must wait for a battery event to occur. Is there a way to nudge this to get it working or simply run some code to see what the battery level was on the last broadcast?

Answer 1

Is there a way to nudge this to get it working or simply run some code to see what the battery level was on the last broadcast?

You can call registerReceiver() with your IntentFilter and a null BroadcastReceiver to get the last-broadcast Intent. This works because ACTION_BATTERY_CHANGED is a so-called "sticky broadcast", which I describe a bit more in this StackOverflow question-and-answer.

Answer 2

This is how to get the battery level without registering a receiver:

Intent batteryIntent = context.getApplicationContext().registerReceiver(null,
                    new IntentFilter(Intent.ACTION_BATTERY_CHANGED));
int rawlevel = batteryIntent.getIntExtra("level", -1);
double scale = batteryIntent.getIntExtra("scale", -1);
double level = -1;
if (rawlevel >= 0 && scale > 0) {
    level = rawlevel / scale;
}

It can use a null BroadcastReceiver because of the sticky nature of the broadcast.

It uses the getApplicationContext() trick in case you are in a intent receiver and get the exception:

android.content.ReceiverCallNotAllowedException: IntentReceiver components are not allowed to register to receive intents