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

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...
}

Answer 2

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)); 
    }
}