How to cast context into listener in BroadcastReceiver's onReceive which is registering from Fragment?

Question

This is the BroadcastReceiver in which context is cast into listener interface:

public class StatusChangeReceiver extends BroadcastReceiver {
    private IStatusChangeListener listener;

    @Override
    public void onReceive(Context context, Intent intent) {
        listener = (IStatusChangeListener) context; // getting error in this line when using LocalBroadcastManager

        if (NetworkUtil.isNetworkConnected()) {
            listener.onConnected();
        } else {
            listener.onDisconnected();
        }
    }
}

This is the interface:

public interface IStatusChangeListener {
    void onConnected(String status);
    void onDisonnected(String status);
}

Now I'm implementing the IStatusChangeListener interface in a Fragment like below:

public class MainFragment extends Fragment implements IStatusChangeListener {
    //some codes

    @Override
    public void onViewCreated(View view, Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);
        StatusChangeReceiver r = new StatusChangeReceiver();
        LocalBroadcastManager.getInstance(getContext()).registerReceiver(r, new IntentFilter("connectionStatus"));
        //getContext().registerReceiver(r, new IntentFilter("connectionStatus"));
    }

    @Override
    void onConnected(String status) {
        //some log here
    }

    @Override
    void onDisonnected(String status) {
        //some log here
    }
}

When I use getContext().registerReceiver(r, new IntentFilter("connectionStatus")); then I get no error but I get no call in the implemented listener's methods in the Fragment.

When I use LocalBroadcastManager.getInstance(getContext()).registerReceiver(r, new IntentFilter("connectionStatus")); then I get java.lang.ClassCastException error:

<ContextName> cannot be cast to IStatusChangeListener

So what is the solution to overcome this problem? Is there any standard way to implement BroadcastReceiver which casts context into listener?

Answer 1

You have to check if the context is instance of IStatusChangeListener or not.

public class StatusChangeReceiver extends BroadcastReceiver {
    private IStatusChangeListener listener;

    @Override
    public void onReceive(Context context, Intent intent) {
        if(context instanceof IStatusChangeListener){
           
        listener = (IStatusChangeListener) context; // getting error in this line //when using LocalBroadcastManager

        if (NetworkUtil.isNetworkConnected()) {
            listener.onConnected();
        } else {
            listener.onDisconnected();
        }
        }
    }
}

In your activity

public class YourActivity extends AppCompatActivity implements IStatusChangeListener {

    MainFragment mainFragment;
    
    @Override
    public void onConnected(String status) {
        if (mainFragment!=null){
            mainFragment.onConnected();
        }
    }

    @Override
    public void onDisonnected(String status) {
        if (mainFragment!=null) {
            mainFragment.onDisonnected();
        }
    }

 @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_home);
        mainFragment = MainFragment();
        //do fragment trasaction
        //get transaction
       transaction.replace(R.id.fragment_container, mainFragment ); transaction.commit();

}
}

Answer 2

You can try the following,

public class SomeClass implements IStatusChangeListener,Parcelable {
  // implement the required methods
}

Activity class

SomeClass someclass = new SomeClass();

intent.putExtra("someclass",someclass)

Reciever Class

    @Override
    public void onReceive(Context context, Intent intent) {
        Bundel b = intent..getExtras()

        if(b != null){
         SomeClass someclass = b.getParcelable("someclass");

        //rest of your logic
       }
    }

Edit:

just put the instance of the SomeClass in the intent which you will be wrapping with a PendingIntent and you can use the intent and the rest of the logic remains same and by this way your MainActivity need not to implement IStatusChangeListener

Answer 3

After searching for hours for the appropriate way to implement such a solution to this problem, I've found a way finally.

In this way, a setListener() method is exposed so that Fragment or Activity can set the listener by sending an instance of IStatusChangeListener .

public class StatusChangeReceiver extends BroadcastReceiver {
    private IStatusChangeListener listener;

    public void setListener(IStatusChangeListener listener) {
        this.listener = listener;
    }

    @Override
    public void onReceive(Context context, Intent intent) {
        if (NetworkUtil.isNetworkConnected()) {
            listener.onConnected();
        } else {
            listener.onDisconnected();
        }
    }
}

This is the interface:

public interface IStatusChangeListener {
    void onConnected(String status);
    void onDisonnected(String status);
}

Now, it is required to have an instance of IStatusChangeListener interface instead of implementing the IStatusChangeListener interface. And then, pass this instance of IStatusChangeListener to setListener() method.

public class MainFragment extends Fragment { //Not implementing the interface

    private IStatusChangeListener listener = new IStatusChangeListener() {
        @Override
        void onConnected(String status) {
            //some log here
        }

        @Override
        void onDisonnected(String status) {
            //some log here
        }
    }

    @Override
    public void onViewCreated(View view, Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);

        StatusChangeReceiver r = new StatusChangeReceiver();
        r.setListener(listener); // pass the IStatusChangeListener instance
        LocalBroadcastManager.getInstance(getContext()).registerReceiver(r, new IntentFilter("connectionStatus"));
    }
}

Note: Always use LocalBroadcastManager if you register BroadcastReceiver from Fragment .