Broadcast Receiver not being called

Question

I am trying to build a simple app that will wait until a new SMS arrives, extract and process the data from it. The application should run in the background. The GUI has a single switch element to start/stop the broadcast receiver. Even if the app is destroyed and the screen is locked, the app should still be working unless the user manually turns it off. I searched every resource on stackoverflow, and most of them did it this way, yet, it still does not work for me, and I can't seem to know why. I know because Log.d(...) is not returning anything. Any help would be appreciated.

Broadcast SMS Receiver

public class SMSReceiver extends BroadcastReceiver {
    @Override
    public void onReceive(Context context, Intent intent) {
        Log.d("RECEIVER", "ENTERED");

        if(intent.getAction().equals("android.provider.Telephony.SMS_RECEIVED")){
            Log.d("RECEIVER", "SMS RECEIVED");

            SmsMessage[] messages = Telephony.Sms.Intents.getMessagesFromIntent(intent);
            for(int i = 0; i < 4; i++){
                SmsMessage sms = messages[i];
                Log.d("Message " + i + 1 + " from: ", sms.getOriginatingAddress());
                Toast.makeText(context,"SMS from " + sms.getOriginatingAddress(), Toast.LENGTH_SHORT).show();
            }
        }

    }
}

Main Activity

public class MainActivity extends AppCompatActivity {
    IntentFilter filter;
    SMSReceiver receiver;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        filter = new IntentFilter();
        filter.addAction("android.provider.Telephony.SMS_RECEIVED");
        receiver = new SMSReceiver();

        Switch startSwitch = (Switch) findViewById(R.id.startSwitch);
        startSwitch.setChecked(false);

        startSwitch.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
            @Override
            public void onCheckedChanged(CompoundButton compoundButton, boolean isChecked) {
                if(isChecked){
                    getApplication().registerReceiver(new SMSReceiver(), filter);
                } else {
                    getApplication().unregisterReceiver(receiver);
                }
            }
        });

    }
}

Manifest

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.ahmad.smsforwarder">

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>

    </application>

    <uses-permission android:name="android.permission.RECEIVE_SMS" />
    <uses-permission android:name="android.permission.READ_SMS" />

</manifest>

Answer 1

You have to register your receiver in AndroidManifest.xml with specific intent in intent filter.

    <receiver
        android:name=".SMSReceiver"
        android:enabled="true"
        android:exported="true">
        <intent-filter>
            <action android:name="android.provider.Telephony.SMS_RECEIVED" />
        </intent-filter>
    </receiver>

Answer 2

I suffered too long to find out that as of Android 6.0 (API 23), you will have to register permissions in the main activity java class as well. I fixed the problem by adding the following lines to the main activity's class onCreate() Method:

ActivityCompat.requestPermissions(this,new String[]{Manifest.permission.READ_SMS},1);
ActivityCompat.requestPermissions(this,new String[]{Manifest.permission.RECEIVE_SMS},1);