callbackFlow with Firebase — convert RealtimeDatabase callbacks to callbackFlow | by Saqib | April 2023

A Information to When/Why/How you can Create callbackFlow . It explains find out how to convert Firebase RealtimeDatabase name again callbackFlow.

This story will take Firebase RealtimeDatabasefor instance to point out the usage of callbackFlow with an actual information stream. On the finish of the story, we are able to apply this information to transform any library callbacks into Kotlin Flows utilizing callbackFlow.

Permits to see an outline of the web page content material

Content material

• overview Move And channelFlow
• callbackFlow featured
• Why/When to make use of callbackFlow ?
• callbackFlow Below the hood
• Firebase Setup and Dependencies — (this step is simply in case if you wish to attempt Firebase realtime database your self utilizing the offered github venture, In any other case you possibly can skip this step and transfer on to the subsequent one)
• firebase RealtimeDatabase name again
• convert RealtimeDatabase name again callbackFlow
• How you can accumulate callbackFlow ?
• Github venture

Overview of Move and channelFlow

The story expects a fundamental understanding of Move, channelFlow And callbackFlow.

Fast overview of Move And channelFlow to know clearly callbackFlow and its utilization.

• Move is the underlying stream of information emitted then collected and many others in sequence. After lambda play is full Move would not emit any extra worth and it is closed
• channelFlow just like Move however with a buffer and buffer measurement of 64, it permits a number of values ​​to be emitted earlier than every emitted worth is collected. It additionally behaves in the identical method as Move in its default utilization i.e. it stops emitting values ​​after going out of the scope of the lambda, however in channelFlow we are able to nonetheless cease closing lambda utilizing awaitClose api inside lambda and ship following worth with predefined methodology. However this isn’t best selection for circumstances the place we need to accumulate information from any callback holding Move alive and might ship information later.

callbackFlow Options

callbackFlow guarantee that awaitClose known as inside lambda(awaitClose is necessary in callbackFlow Not like channelFlow ) preserve Move alive, to ship the info at any later time, and to have the ability to unsubscribe any listener when it’s destroyed.

Why/When to make use of callbackFlow?

If you wish to learn the info as soon as, you in all probability do not want it callbackFlow one shot you possibly can nonetheless get the conventional phrase Move or coroutines and don’t have to do callbackFlow suppose, I feel.

callbackFlow is a perfect selection once we need to learn information periodically from any callback. For instance, the next are functions (however should not restricted to) of callbackFlow

• Learn community standing on system — (take a number of photographs)
• Learn system location information — (a number of seize)
• Deal with any Third Occasion library callbacks which can be offering real-time information e.g. Firebase callbacks – (a number of occasions)

callbackFlow UnderTheHood

Let’s examine how callbackFlow be executed.

public enjoyable  callbackFlow(@BuilderInference block: droop ProducerScope.() -> Unit): Move = CallbackFlowBuilder(block)

Undergo the details beneath.

1. callbackFlow use CallbackFlowBuilder class to create
2. CallbackFlowBuilder class is overriding ChannelFlowBuildermeaning it is constructed on channelFlow .
3. callbackFlow request for offering awaitClose inside block to verify the stream continues to be lively and might unregister the inside listener awaitClose code block to verify callbackFlow unregister the listener when it’s canceled/closed in any other case the listener might leak.
4. callbackFlow will elevate IllegalStateException if we is not going to ship awaitClose so it ensures awaitClose Existence block just isn’t like channelFlow.

Firebase Setup and Dependencies

To attempt it out for your self it is advisable arrange a Firebase account, when you do not need to attempt it now you possibly can transfer on to the subsequent part to see code examples, if not, do the next.

1. go to Firebase Dashboard and Create a Firebase venture
2. Register your Android app with Firebase venture utilizing instruct.
3. After registering your Android app with the Firebase venture, it is possible for you to to obtain the configuration file google-services.json Add that file to your application-level root listing
4. To allow Google providers, add the next Google providers plugin root-level construct.gradle file as construct script dependency

5. On the utility degree construct.gradle add google providers plugin

6. Add the Firebase SDK to your app degree construct.gradle

7. Create RealtimeDatabase in your Firebase console venture. After creating you’ll get the database path, We’ll want that path to create reference to RealtimeDatabase

Firebase Realtime Database Callback

firebase RealtimeDatabase present listener callbacks to offer information in actual time. We’ll subscribe to actual time information updates as proven within the code beneath.

Take a look at the callbacks RealtimeDatabase offered to learn information from the database.

Within the above code, we’re creating FirebaseDatabase instance after which subscribe ValueEventListener to learn up to date information from the database in onDataChange provide callback dataSnapShot of time. It provides the primary information as quickly as we enroll ValueEventListener after which it supplies updates as quickly as information is up to date/added/eliminated. So the callbacks might be known as at any time in actual circumstances.

convert RealtimeDatabase name again callbackFlow

We need to convert these callbacks to Kotlin callbackFlow. Check out the code beneath that does that and undergo it afterwards. To make use of coroutine Streams it is advisable add the next dependency.

implementation 'org.jetbrains.kotlinx:kotlinx-coroutines-core:1.7.0-RC'

And the code seems like beneath

Take a look at the adjustments we made to transform callbacks to callbackFlow

• Use a return perform like Move .
• callbackFlow the return block, the inside block creates the database reference and subscribes it to the database reference to hear for updates within the callbacks.
• trySend(worth?.toString().orEmpty()) inside assertion onDataChange the callback will ship the worth to the collector callbackFlow .
• awaitClose get a block of code to unregister the occasion listener when callbackFlow Canceled.

How you can accumulate callbackFlow?

Assortment about callbackFlow should be executed in life-cycle-aware however as a result of we are able to nonetheless get information in these callbacks when the app is within the background or if the consumer strikes away from the display screen and we’re nonetheless listening to these streams unknowingly.

IN generally, all threads ought to be collected in a lifecycle-aware method, which is the really useful strategy.

The code beneath exhibits accumulate callbackFlow when the view is included Resumed state in any other case it can cease gathering.

supply

Github venture

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