How to handle notifications with FCM when app is i

问题:

I used firebase to build My project.
It will also use the FCM (firebase cloud message).
But there is a problem.
I can't handle the FCM (create my custom notificaion) when app is in background.

The official site tutorial said that
case 1: App foreground -> override the "onMessageReceived()" to create your custom notification.
case 2: App background -> System will create the notification directly. We needn't and can't do anything. Because it doesn't trigger the "onMessageReceived()" in this case.

However if I can do nothing when app is background, I can't create my custom notification. (e.g. After Users click the notification and it will pop up a window to show detail information.)

So how do I handle notifications with FCM when app is in background?

回答1:

There is a bad news.
Google change the Firebase source code in version 'com.google.firebase:firebase-messaging:11.6.0'.
handelIntent is "public final void method" now. which means we can't override it .
If you want to use the solution, change the version to be "com.google.firebase:firebase-messaging:11.4.2"

Try my way. It can perfectly work on the project build version is Android 6.0 above(api level 23) and I have tried it already.

There is better way than official site tutorial

The official site said that the notification will be created by system when app is in background. So you can't handle it by overriding the "onMessageReceived()". Because the "onMessageReceived()" is only triggered when app is in foreground.

But the truth is not. Actually the notificaions (when app is in background) are created by Firebase Library.

After I traced the firebase library code. I find a better way.

Step 1. Override the "handleIntent()" instead of "onMessageReceived()" in FirebaseMessagingService
why:
Because the method will be trigger either app is in foreground or the background. So we can handle FCM message and create our custom notifications in both cases.

@Override
public void handleIntent(Intent intent) {
    Log.d( "FCM", "handleIntent ");
}

Step 2. Parse the message from FCM
how:
If you don't know the format of the message you set. Print it and try to parse it.
Here is the basic illustration

Bundle bundle = intent.getExtras();
if (bundle != null) {
    for (String key : bundle.keySet()) {
        Object value = bundle.get(key);
        Log.d("FCM", "Key: " + key + " Value: " + value);
    }
}

Step 2. Remove the notifications created by Firebase library when the app is in background
why:
We can create our custom notification. But the notification created by Firebase Library will still be there (Actually it created by ""super.handleIntent(intent)"". There is detail explaination below.). Then we'll have two notifcations. That is rather weird. So we have to remove the notificaion created by Firebase Library

how (project build level is Android 6.0 above):
Recognize the notifications which we want to remove and get the informaion. And use the "notificationManager.cancel()" to remove them.

private void removeFirebaseOrigianlNotificaitons() {

    //check notificationManager is available
    NotificationManager notificationManager = 
        (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);
    if (notificationManager == null )
        return;

    //check api level for getActiveNotifications()
    if (Build.VERSION.SDK_INT < Build.VERSION_CODES.M) {
        //if your Build version is less than android 6.0
        //we can remove all notifications instead. 
        //notificationManager.cancelAll();
        return;
    }


    //check there are notifications
    StatusBarNotification[] activeNotifications = 
        notificationManager.getActiveNotifications();
    if (activeNotifications == null)
        return;

    //remove all notification created by library(super.handleIntent(intent))
    for (StatusBarNotification tmp : activeNotifications) {
        Log.d("FCM StatusBarNotification", 
            "StatusBarNotification tag/id: " + tmp.getTag() + " / " + tmp.getId());
        String tag = tmp.getTag();
        int id = tmp.getId();

        //trace the library source code, follow the rule to remove it.
        if (tag != null && tag.contains("FCM-Notification"))
            notificationManager.cancel(tag, id);
    }
}

The my whole sample code:

public class MyFirebaseMessagingService extends FirebaseMessagingService {

private static int notificationCount=0;

@Override
public void handleIntent(Intent intent) {
    //add a log, and you'll see the method will be triggered all the time (both foreground and background).
    Log.d( "FCM", "handleIntent");

    //if you don't know the format of your FCM message,
    //just print it out, and you'll know how to parse it
    Bundle bundle = intent.getExtras();
    if (bundle != null) {
        for (String key : bundle.keySet()) {
            Object value = bundle.get(key);
            Log.d("FCM", "Key: " + key + " Value: " + value);
        }
    }

    //the background notification is created by super method
    //but you can't remove the super method. 
    //the super method do other things, not just creating the notification
    super.handleIntent(intent);

    //remove the Notificaitons
    removeFirebaseOrigianlNotificaitons();

    if (bundle ==null)
        return;

    //pares the message
    CloudMsg cloudMsg = parseCloudMsg(bundle);

    //if you want take the data to Activity, set it
    Bundle myBundle = new Bundle();
    myBundle.putSerializable(TYPE_FCM_PLATFORM, cloudMsg);
    Intent myIntent = new Intent(this, NotificationActivity.class);
    myIntent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
    myIntent.putExtras(myBundle);
    PendingIntent pendingIntent = PendingIntent.getActivity(this, notificationCount, myIntent, PendingIntent.FLAG_UPDATE_CURRENT);

    //set the Notification
    NotificationCompat.Builder notificationBuilder = new NotificationCompat.Builder(this)
            .setSmallIcon(R.mipmap.icon)
            .setContentTitle(cloudMsg.getTitle())
            .setContentText(cloudMsg.getMessage())
            .setAutoCancel(true)
            .setContentIntent(pendingIntent);

    NotificationManager notificationManager = (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);
    notificationManager.notify(notificationCount++, notificationBuilder.build());
}



/**
 * parse the message which is from FCM
 * @param bundle
 */
private CloudMsg parseCloudMsg(Bundle bundle) {
    String title = null, msg=null;

    //if the message is sent from Firebase platform, the key will be that
    msg = (String) bundle.get("gcm.notification.body");

    if(bundle.containsKey("gcm.notification.title"))
    title = (String) bundle.get("gcm.notification.title");

    //parse your custom message
    String testValue=null;
    testValue =  (String) bundle.get("testKey");

    //package them into a object(CloudMsg is your own structure), it is easy to send to Activity.
    CloudMsg cloudMsg = new CloudMsg(title, msg, testValue);
    return cloudMsg;
}


/**
 * remove the notification created by "super.handleIntent(intent)"
 */
    private void removeFirebaseOrigianlNotificaitons() {

    //check notificationManager is available
    NotificationManager notificationManager = 
        (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);
    if (notificationManager == null )
        return;

    //check api level for getActiveNotifications()
    if (Build.VERSION.SDK_INT < Build.VERSION_CODES.M) {
        //if your Build version is less than android 6.0
        //we can remove all notifications instead. 
        //notificationManager.cancelAll();
        return;
     }

    //check there are notifications
    StatusBarNotification[] activeNotifications = 
        notificationManager.getActiveNotifications();
    if (activeNotifications == null)
        return;

    //remove all notification created by library(super.handleIntent(intent))
    for (StatusBarNotification tmp : activeNotifications) {
        Log.d("FCM StatusBarNotification", 
            "tag/id: " + tmp.getTag() + " / " + tmp.getId());
        String tag = tmp.getTag();
        int id = tmp.getId();

        //trace the library source code, follow the rule to remove it.
        if (tag != null && tag.contains("FCM-Notification"))
            notificationManager.cancel(tag, id);
    }
}
}

回答2:

However if I can do nothing when app is background, I can't create my custom notification. (e.g. After Users click the notification and it will pop up a window to show detail information.)

So how do I handle notifications with FCM when app is in background?

First, you need to create correct message payload that you send to fcm server. Example:

{
  "to": "topic_name",
  "priority": "high",
  "data": {
    "field1": "field1 value" 
    "field2": "field2 value" 
  }

  "notification" : {
      "body" : "Lorem ipsum",
      "title" : "sampke title" 
      "click_action": "SHOW_DETAILS" 
    }
}

data payload is actual data you want to show as message details after user clicks on notification, notification payload represents how generated notification should look (there are much more attributes possible to set), you don't need to build notification by yourself, you only need to set it properties here.

To show your activity after user taps on notication, you need to set intent filter corresponding to click_action:

<intent-filter>
     <action android:name="SHOW_DETAILS"/>
     <category android:name="android.intent.category.DEFAULT"/>
 </intent-filter>

so activity that have above intent filter will be launched automatically when user taps to notification. Last step is to retrieve data when activity is launched after notification tap. It's pretty easy. Custom data is passed to activity via bundle. Inside onCreate method for your activity do something like that:

Bundle bundle = getIntent().getExtras();
if(bundle.getString("action").equals("SHOW_DETAILS")) /*This indicates activity is launched from notification, not directly*/
{
 //Data retrieved from notification payload send 
 String filed1 = bundle.getString("field1");
 String filed2 = bundle.getString("field2");
}

All of above is valid if app is not running or it's in background. If your app is foreground, no notification will be created. Instead, you will receive onMessageReceived() event so you can handle the same data there (I guess you know how).

Reference:

https://firebase.google.com/docs/cloud-messaging/http-server-ref https://github.com/firebase/quickstart-android/tree/master/messaging

回答3:

You need to use FCM data messages in order to create custom notification in a android app.Even your app is in background, onMessageReceived will be called, so you can process the data and show the custom notification.

https://firebase.google.com/docs/cloud-messaging/android/receive

Data message format which has to be sent from server:

{"message":{
"token":"Your Device Token",
"data":{
  "Nick" : "Mario",
  "body" : "great match!",
  "Room" : "PortugalVSDenmark"
}
}
}

回答4:

FCM Won't send a background notification if your app is killed any more, and as you described in your answer about the handleIntent() solution It may work for some devices and for some old version of the FCM, also if you @override method that doesn't described in the official doc's of firebase you may struggle some problems here, and you use it on your own risk!.

What is the solution?

You need to use your own push-notification-service beside FCM like Telegram.

OR using SyncAdapter beside GCM like Gmail.

So if you need it to work successfully like those apps, you have to use your own hack.