Android - Ayuda con notificaciones Firebase

package com.example.ricardo.sansano;

import android.util.Log;

import com.google.firebase.iid.FirebaseInstanceId;

import com.google.firebase.iid.FirebaseInstanceIdService;

public class FirebaseService extends FirebaseInstanceIdService {

    @Override

    public void onTokenRefresh() {

        super.onTokenRefresh();

        // Get updated InstanceID token.

        String refreshedToken = FirebaseInstanceId.getInstance().getToken();

        Log.e("Refreshed token: ", refreshedToken);

        // If you want to send messages to this application instance or

        // manage this apps subscriptions on the server side, send the

        // Instance ID token to your app server.

        //sendRegistrationToServer(refreshedToken);

    }

}

package com.example.ricardo.sansano;

import android.app.NotificationManager;

import android.app.PendingIntent;

import android.app.Service;

import android.content.Context;

import android.content.Intent;

import android.media.RingtoneManager;

import android.net.Uri;

import android.os.IBinder;

import android.support.v4.app.NotificationCompat;

import android.util.Log;

import com.google.firebase.iid.FirebaseInstanceId;

import com.google.firebase.iid.FirebaseInstanceIdService;

import com.google.firebase.messaging.FirebaseMessagingService;

import com.google.firebase.messaging.RemoteMessage;

public class Receive extends FirebaseMessagingService {

    @Override

    public void onMessageReceived(RemoteMessage remoteMessage) {

        // ...

        super.onMessageReceived(remoteMessage);

        //String cuerpo = remoteMessage.getNotification().getBody();

        // TODO(developer): Handle FCM messages here.

        // Not getting messages here? See why this may be: https://goo.gl/39bRNJ

        //Log.e("From: ", remoteMessage.getFrom());

        //Log.e("Message: " , cuerpo);

        if (remoteMessage.getNotification() != null) {

            mostrarNotificacion(remoteMessage.getNotification().getBody(), remoteMessage.getNotification().getTitle());

        }

        // Check if message contains a data payload.

        //

        // Check if message contains a notification payload.

        //if (remoteMessage.getNotification() != null) {

        //}

        // Also if you intend on generating your own notifications as a result of a received FCM

        // message, here is where that should be initiated. See sendNotification method below.

    }

    private void mostrarNotificacion(String body, String title) {

        Intent i = new Intent(this, MainActivity.class);

        i.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);

        PendingIntent pendingIntent = PendingIntent.getActivity(this, 0, i, PendingIntent.FLAG_ONE_SHOT);

        Uri sonido = RingtoneManager.getDefaultUri(RingtoneManager.TYPE_NOTIFICATION);

        NotificationCompat.Builder notificacion = new NotificationCompat.Builder(this)

                .setContentTitle(title)

                .setContentText(body)

                .setAutoCancel(true)

                .setSound(sonido)

                .setContentIntent(pendingIntent);

        NotificationManager manager = (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);

        manager.notify(0, notificacion.build());

    }

}

<?xml version="1.0" encoding="utf-8"?>

<manifest xmlns:android="http://schemas.android.com/apk/res/android"

    package="com.example.ricardo.sansano">

    <application

        android:allowBackup="true"

        android:icon="@mipmap/ic_launcher"

        android:label="@string/app_name"

        android:roundIcon="@mipmap/ic_launcher_round"

        android:supportsRtl="true"

        android:theme="@style/AppTheme">

        <activity

            android:name=".MainActivity"

            android:label="@string/app_name"

            android:theme="@style/AppTheme.NoActionBar">

            <intent-filter>

                <action android:name="android.intent.action.MAIN" />

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

            </intent-filter>

        </activity>

        <service android:name=".FirebaseService">

            <intent-filter>

                <action android:name="com.google.firebase.INSTANCE_ID_EVENT" />

            </intent-filter>

        </service>

        <service

            android:name=".Receive">

            <intent-filter>

                <action android:name="com.google.firebase.MESSAGING_EVENT"/>

            </intent-filter>

        </service>

    </application>

</manifest>

// Top-level build file where you can add configuration options common to all sub-projects/modules.

buildscript {

    repositories {

        google()

        jcenter()

    }

    dependencies {

        classpath 'com.google.gms:google-services:4.0.0'

        classpath 'com.android.tools.build:gradle:3.1.3'

        // NOTE: Do not place your application dependencies here; they belong

        // in the individual module build.gradle files

    }

}

allprojects {

    repositories {

        google()

        jcenter()

    }

}

task clean(type: Delete) {

    delete rootProject.buildDir

}

apply plugin: 'com.android.application'

android {

    compileSdkVersion 27

    defaultConfig {

        applicationId "com.example.ricardo.sansano"

        minSdkVersion 15

        targetSdkVersion 27

        versionCode 1

        versionName "1.0"

        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"

    }

    buildTypes {

        release {

            minifyEnabled false

            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'

        }

    }

}

dependencies {

    implementation fileTree(dir: 'libs', include: ['*.jar'])

    implementation 'com.android.support:appcompat-v7:27.1.1'

    implementation 'com.android.support:design:27.1.1'

    implementation 'com.android.support.constraint:constraint-layout:1.1.2'

    implementation 'com.google.firebase:firebase-messaging:11.8.0'

    testImplementation 'junit:junit:4.12'

    androidTestImplementation 'com.android.support.test:runner:1.0.2'

    androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.2'

    implementation 'com.google.firebase:firebase-core:11.8.0'

}

apply plugin: 'com.google.gms.google-services'