Register BroadcastReceiver in non-activity class

Question

I have to use a BroadcastReceiver in a class that I will have to call in an Activity. Obviously, I have to necessarily register the BroadcastReceiver and then I wrote this code:

    public class MyClassName {

        Context context;
        BroadcastReceiver batteryInfoReceiverLevel;

        public void CheckBatteryLevel() {

        Log.d("App", "I'm in the CheckBatteryLevel");

        context.registerReceiver(batteryInfoReceiverLevel, new IntentFilter(Intent.ACTION_BATTERY_CHANGED));

        batteryInfoReceiverLevel = new BroadcastReceiver() {

            @Override
            public void onReceive(Context context, Intent intent) {

            Log.d("Apps", "I'm in the onReceive");

            int level= intent.getIntExtra(BatteryManager.EXTRA_LEVEL,0);

            if(level <=100) {
//Do something

            }

            else if(level >=100) {
//Do something
            }

            }

            };

        }

    }

When I run the code the application crashes giving "Error receiving broadcast Intent { act=android.intent.action.BATTERY_CHANGED flg=0x60000010 (has extras) } and the crash line is

context.registerReceiver(batteryInfoReceiverLevel, new IntentFilter(Intent.ACTION_BATTERY_CHANGED));

How can i fix?

Answer 1

There are two problems here:

ρяσѕρєя K has pointed out the first one:

Initialize your context by adding a parameter to the method CheckBatteryLevel() or to the constructor of MyClass

public class MyClass(Context ctx) {
    context = ctx;
}

Second, you have to call registerReceiver(..) AFTER you have initialized the BroadcastReceiver. Or it will be null and not registered.

All in all this should do it:

public class MyClassName {

    BroadcastReceiver batteryInfoReceiverLevel;

    public void CheckBatteryLevel(Context ctx) {

        Log.d("App", "I'm in the CheckBatteryLevel");

        batteryInfoReceiverLevel = new BroadcastReceiver() { // init your Receiver

            @Override
            public void onReceive(Context context, Intent intent) {

                Log.d("Apps", "I'm in the onReceive");
                int level= intent.getIntExtra(BatteryManager.EXTRA_LEVEL,0);
                if(level <=100) {
                    //Do something
                } else if(level >=100) {
                    //Do something
                }
            }
        };
        // register your Receiver after initialization 
        ctx.registerReceiver(batteryInfoReceiverLevel,
                  new IntentFilter(Intent.ACTION_BATTERY_CHANGED)); 
    }
}

Answer 2

application crashes giving "Error receiving broadcast Intent

Because context is null you should need to initialize context before calling registerReceiver. for initialization use Class constructor or pass to CheckBatteryLevel method from calling Activity. :

public void CheckBatteryLevel(Context aContext) {

context =aContext;
//....your code here...
}