Develop Reference

About send notification to other app through FCM [duplicate]

I have an Android app, and I want it be able to receive push notifications from two different Firebase projects.
I read the blog "Working with multiple Firebase projects in an Android app" https://firebase.googleblog.com/2016/12/working-with-multiple-firebase-projects-in-an-android-app.html which talks about "Accessing the Databases from two different Firebase projects".
However, there is no info about receiving notifications from multiple Firebase projects.
So, how to integrate my app with multiple Firebase projects and receive push notifications from them?

There is actually a part in the documentation about this topic:
Receiving messages from multiple senders
FCM allows multiple parties to send messages to the same client app. For example, suppose the client app is an article aggregator with multiple contributors, and each of them should be able to send a message when they publish a new article. This message might contain a URL so that the client app can download the article. Instead of having to centralize all sending activity in one location, FCM gives you the ability to let each of these contributors send its own messages.
To make this possible, make sure each sender generates its own sender ID. See the client documentation for your platform for information on on how to obtain the FCM sender ID. When requesting registration, the client app fetches the token multiple times, each time with a different sender ID in audience field.
Finally, share the registration token with the corresponding app servers (to complete the FCM registration client/server handshake), and they'll be able to send messages to the client app using their own authentication keys.
Note that there is limit of 100 multiple senders.
I think the confusing but important part here is:
When requesting registration, the client app fetches the token multiple times, each time with a different sender ID in audience field.
In other terms, you'll have to call getToken() passing the Sender ID and simply "FCM" (e.g. getToken("2xxxxx3344", "FCM")) as the parameters. You'll have to make sure that you call this for each sender (project) that you need.
Also, note from the getToken() docs:
This is a blocking function so do not call it on the main thread.
Some additional good-to-knows:
It does not auto retry if it fails like the default one.
It returns an IOException when it fails.

I had some issues when implementing the accepted answer and hence went ahead and tried to do it on my own when I came to find a robust solution. I have shared in detail there solution here.

Should I store Android device tokens for sending push notifications?

I am working on an app, which requires Android push notifications to be implemented.
I have decided to use Firebase Cloud Messaging directly; without using any other abstraction such as AWS SNS or Pusher.
I would like to avoid storing and managing device tokens in the backend, by using the following approach.
In the android app.
When the user logs into the android application, obtain device token but not send it to the server.
Subscribe to a topic that is based on a agreed convention, such that the topic is unique to that user.
On logout unsubscribe from the topic.
In the Server.
Whenever a situation arises to send a notification to particular user, send push notification to the topic, that is based on the convention.
I would like to know if this is a viable strategy to avoid managing device tokens ?
Case against using topics.
From the official docs.
Based on the publish/subscribe model, FCM topic messaging allows you to send a message to multiple devices that have opted in to a particular topic. You compose topic messages as needed, and FCM handles routing and delivering the message reliably to the right devices.
For example, users of a local weather forecasting app could opt in to a "severe weather alerts" topic and receive notifications of storms threatening specified areas. Users of a sports app could subscribe to automatic updates in live game scores for their favorite teams.
I see that topics are recommended, when multiple devices are to be notified. But I have decided to create a topic per user, this would mean most topics would end up getting subscribed by only one device; Is this approach ok ?

I see that topics are recommended, when multiple devices are to be notified
Yes, multiple devices that have something common to listen to, which is the topic. Topics are used for messages that could be received by the general clients since it is public -- i.e. anyone could subscribe and receive messages sent to it.
What is advised to use for multiple devices, but for the same user is to use Device Groups (see my answer here for tips on Managing Device Groups). However, if you don't mind the "topics being public" part, then your approach should be fine.

Yes, Here required device tokens if we want to send push notification whoever installed your app.
My research we can save device tokens in back end at first time installation of your app that is better according to my understanding so that we can easy to send push notification across all devices.

Correct way to address messages

Let's say I have an Android app with 100 users that I don't know personally. Is it right to make each one of them subscribe to topics like FirebaseMessaging.getInstance().subscribeToTopic("<company_id>_<user_id>"); so I can address them and send notifications for one or two specifically or there is a better way to do that?

If you intend to send a message to specific users only, you could simply go ahead and use to or registration_ids when targeting the specific users. registration_ids has a limit of 1000 tokens per request.
As per the topics, it was designed to easily send messages to its subscribers. Depending on your use-case, it could be fine to subscribe them. However, you should still keep the registration tokens for each user in case you need to send specific messages.

It all depends on your goal.
Anyone can subscribe to a topic, so you should only use those for sending messages targeted-but-public messages. While you can counter this a bit by making the topic names hard to guess, the inherent behavior of topics is that you lose control over precisely what devices are targeted in return for having to write less code.
If you send to a token in your own code, you determine precisely who receives the message. But you will have to run the code that maps the message to the tokens yourself.

I think the answers are pretty clear, I would only like to add that, this method of subscription it can be easily combined with the Firebase web console. If you want to quickly send a message to any topic, the topic is created on registration, so you only have to know the topic name.
In the Firebase Web Console, you can find the target, an application, a token for a device or a topic. If you choose a topic, just write the topic name. There is an error which always says there is no topic, disregard it, and click send, the push will be sent and the subscribers will get their notifications.

Limit of Bulk Firebase Cloud Messaging

We are trying to sending promotional push messages to 8k different devices. We are getting success in response to the push notification URL https://fcm.googleapis.com/fcm/send
But only some of the users are getting this notification and not all. So is there any limitation in Firebase Cloud Messaging to send bulk push as i tried to find on Firebase documentation, but it is not written anywhere.
I tried to get the exact limit suggested by Google, but could not locate to a specific page where in Google has mentioned the limit.
However I have found one link of quora send more than 1000 push messages

According to this answer, the FCM limitations are similar to GCM.
From the GCM documentation:
...It must contain at least 1 and at most 1000 registration tokens.
So you're presumably able to send each message to 1000 devices. Since you're not limited in number of messages, you can send the same message 8 times, to 8 different lists.

#NeriaNachum's answer is referring to sending messages to multiple recipients limit when using the registration_ids parameter. From the FCM docs (which I think is what you were looking for):
This parameter specifies the recipient of a multicast message, a message sent to more than one registration token.
The value should be an array of registration tokens to which to send the multicast message. The array must contain at least 1 and at most 1000 registration tokens. To send a message to a single device, use the to parameter.
Multicast messages are only allowed using the HTTP JSON format.
However, if you use Topics Messaging instead, there is no limit. Just make sure that each of the user you intend to send a message to is properly subscribed. If you have your own App Server, you can subscribe multiple tokens using the Instance ID API (see my answer here).

You can only send it to 500 users in one go.
Better implement batching at your end.
https://firebase.google.com/docs/reference/admin/java/reference/com/google/firebase/messaging/MulticastMessage

Receive push notifications on one android app from two Firebase projects

I have an Android app, and I want it be able to receive push notifications from two different Firebase projects.
I read the blog "Working with multiple Firebase projects in an Android app" https://firebase.googleblog.com/2016/12/working-with-multiple-firebase-projects-in-an-android-app.html which talks about "Accessing the Databases from two different Firebase projects".
However, there is no info about receiving notifications from multiple Firebase projects.
So, how to integrate my app with multiple Firebase projects and receive push notifications from them?

There is actually a part in the documentation about this topic:
Receiving messages from multiple senders
FCM allows multiple parties to send messages to the same client app. For example, suppose the client app is an article aggregator with multiple contributors, and each of them should be able to send a message when they publish a new article. This message might contain a URL so that the client app can download the article. Instead of having to centralize all sending activity in one location, FCM gives you the ability to let each of these contributors send its own messages.
To make this possible, make sure each sender generates its own sender ID. See the client documentation for your platform for information on on how to obtain the FCM sender ID. When requesting registration, the client app fetches the token multiple times, each time with a different sender ID in audience field.
Finally, share the registration token with the corresponding app servers (to complete the FCM registration client/server handshake), and they'll be able to send messages to the client app using their own authentication keys.
Note that there is limit of 100 multiple senders.
I think the confusing but important part here is:
When requesting registration, the client app fetches the token multiple times, each time with a different sender ID in audience field.
In other terms, you'll have to call getToken() passing the Sender ID and simply "FCM" (e.g. getToken("2xxxxx3344", "FCM")) as the parameters. You'll have to make sure that you call this for each sender (project) that you need.
Also, note from the getToken() docs:
This is a blocking function so do not call it on the main thread.
Some additional good-to-knows:
It does not auto retry if it fails like the default one.
It returns an IOException when it fails.

I had some issues when implementing the accepted answer and hence went ahead and tried to do it on my own when I came to find a robust solution. I have shared in detail there solution here.