Cant receive Notifications from FCM while the app is in Foreground state

Question

I am new to Android and programming and I am creating an app that receives messages from FCM and its work normally while the app in the Background, so I have added a FirebaseMessagingService class that receives the notifications in onMessageReceived method and followed out google docs but still the notification does not work while the app in the foreground state, I have followed every step and can't figure out where is the problem in my code as the Logs does not help me and I don't receive any bug expect this one which I don't know if its the source if the problem: Error while parsing timestamp in GCM event java.lang.NumberFormatException: s == null

Here is my MyFirebaseMessagingService class

import android.app.NotificationManager;
import android.app.PendingIntent;
import android.content.BroadcastReceiver;
import android.content.Intent;
import android.support.v4.app.NotificationCompat;
import android.support.v4.app.NotificationManagerCompat;

import com.app.muhammadgamal.swapy.R;
import com.google.firebase.messaging.RemoteMessage;

public class MyFirebaseMessagingService extends com.google.firebase.messaging.FirebaseMessagingService {

    @Override
    public void onMessageReceived(RemoteMessage remoteMessage) {
        super.onMessageReceived(remoteMessage);

        String click_Action = remoteMessage.getNotification().getClickAction();


        String messageTitle = remoteMessage.getNotification().getTitle();
        String messageBody = remoteMessage.getNotification().getBody();


        NotificationCompat.Builder mBuilder = new NotificationCompat.Builder(this, getString(R.string.default_notification_channel_id))
                .setSmallIcon(R.drawable.ic_main_logo)
                .setContentTitle(messageTitle)
                .setContentText(messageBody)
                .setPriority(NotificationCompat.PRIORITY_DEFAULT);


        Intent intent = new Intent(click_Action);
        PendingIntent pendingIntent = PendingIntent.getActivity(this, 0, intent, PendingIntent.FLAG_UPDATE_CURRENT);
        mBuilder.setContentIntent(pendingIntent);


        int mNotificationID = (int)System.currentTimeMillis();
        NotificationManager manager = (NotificationManager)getSystemService(NOTIFICATION_SERVICE);
        manager.notify(mNotificationID,mBuilder.build());

    }
}

and my Manifest File

    <?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.app.muhammadgamal.swapy">

    <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
    <uses-permission android:name="android.permission.INTERNET" />
    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
    <uses-permission android:name="android.permission.ACCESS_WIFI_STATE" />

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_main_logo"
        android:label="@string/app_name"
        android:roundIcon="@drawable/ic_main_logo"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity
            android:name=".Activities.SignInActivity"
            android:theme="@style/AppTheme.NoActionBar">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity
            android:name=".Activities.SignUpActivity"
            android:theme="@style/AppTheme.NoActionBar" />
        <activity
            android:name=".Activities.ProfileActivity"
            android:theme="@style/AppTheme.NoActionBar" />
        <activity
            android:name=".Activities.NavDrawerActivity"
            android:theme="@style/AppTheme.NoActionBar" />
        <activity
            android:name=".Activities.SwapCreationActivity"
            android:theme="@style/AppTheme.NoActionBar" />

        <activity android:name=".Activities.ReceivedSwapRequest">
            <intent-filter>
                <action android:name="com.app.muhammadgamal.swapy.Activities.ReceivedSwapRequest_NOTIFICATION_TASK"></action>
                <category android:name="android.intent.category.DEFAULT"></category>
            </intent-filter>
        </activity>

        <service
            android:name=".Notifications.MyFirebaseMessagingService">
            <intent-filter>
                <action android:name="com.google.firebase.MESSAGING_EVENT"/>
            </intent-filter>
        </service>

    </application>

</manifest>

and my index function

   'use strict'


const functions = require('firebase-functions');
const admin = require('firebase-admin');
admin.initializeApp(functions.config().firebase);


exports.sendNotification = functions.database.ref('/Notifications/{receiver_user_id}/{notification_id}')
.onWrite((data, context) =>
{
    const receiver_user_id = context.params.receiver_user_id;
    const notification_id = context.params.notification_id;


    console.log('We have a notification to send to :' , receiver_user_id);


    if (!data.after.val()) 
    {
        console.log('A notification has been deleted :' , notification_id);
        return null;
    }

    const DeviceToken = admin.database().ref(`/Users/${receiver_user_id}/device_token`).once('value');

    return DeviceToken.then(result => 
    {
        const token_id = result.val();

        const payload = 
        {
            notification:
            {
                title: "New Swap Request",
                body: `you have a new Swap Request, Please Check.`,
                click_action: "com.app.muhammadgamal.swapy.Activities.ReceivedSwapRequest_NOTIFICATION_TASK"
            }
        };

        return admin.messaging().sendToDevice(token_id, payload)
        .then(response => 
            {
                return console.log('This was a notification feature.');
            });
    });
});

Answer 1

I discovered the problem, It was that I am using Android O and didn't set the Channel ID for the notification which is a must if you want to receive it on Android 8.0 or higher

so here is the solution code

 private void createNotificationChannel() {
    // Create the NotificationChannel, but only on API 26+ because
    // the NotificationChannel class is new and not in the support library
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
        CharSequence name = getString(R.string.channel_name);
        String description = getString(R.string.channel_description);
        int importance = NotificationManager.IMPORTANCE_DEFAULT;
        NotificationChannel channel = new NotificationChannel(CHANNEL_ID, name, importance);
        channel.setDescription(description);
        // Register the channel with the system; you can't change the importance
        // or other notification behaviors after this
        NotificationManager notificationManager = getSystemService(NotificationManager.class);
        notificationManager.createNotificationChannel(channel);
    }
}