How and when does the Android system send the ACTION_BATTERY_CHANGED sticky broadcast?

Question

My goal is : when I call some function, I want to get the exact current battery status(level,voltage and etc..).

First I tried to do it in my application as shown on the website. Then I have found actually the ACTION_BATTERY_CHANGED broadcast is sticky which means what I got is from last broadcast, not the exact current value.

Actually, I have looked into the android source code. For the battery interface, the driver has functions to read the registers inside the battery which contain the current soc(state of charge), voltage and etc..

So I am just wondering how and when the system sends the sticky broadcast ACTION_BATTERY_CHANGED? Does it send it periodically(e.g.,every 10 seconds it will read the registers in battery and send the broadcast)? Or does it send based on other criteria(e.g, change of soc, voltage? But voltage will change so frequently in terms of mV)?

To realize my goal, one troublesome way is to implement a system call to call the driver functions and then recompile the NDK to make it usable in my application code. But I just want to know whether I can do this directly through the ACTION_BATTERY_CHANGED broadcast considering what I have mentioned above? Does registering the broadcast again have any effect?

Answer 1

Simply register the Broadcast receiver for the battery level. You will get the result of battery level in onReceive.

private void batteryLevel() {
         BroadcastReceiver batteryLevelReceiver = new BroadcastReceiver() {
                   public void onReceive(Context context, Intent intent) {
                                context.unregisterReceiver(this);
                                int rawlevel = intent.getIntExtra("level", -1);
                                int scale = intent.getIntExtra("scale", -1);
                                int level = -1;
                                if (rawlevel >= 0 && scale > 0) {
                                                   level = (rawlevel * 100) / scale;
                                }
         batterLevel.setText("Battery Level Remaining: " + level + "%");
     }
    };
IntentFilter batteryLevelFilter = new IntentFilter(Intent.ACTION_BATTERY_CHANGED);
registerReceiver(batteryLevelReceiver, batteryLevelFilter);
}

Hope this will help you.