How to Use Isolates in Flutter with Back4app to Handle Heavy Data Processing

introduction flutter is a powerful framework for building cross platform applications, but like many mobile frameworks, it runs all code on a single thread by default this thread, known as the ui thread, is responsible for rendering your app's ui when heavy tasks like data processing or file handling occur on the ui thread, they can cause the app to lag or "jank," leading to a poor user experience to address this, dart provides a feature called isolates isolates allow you to run expensive computations on a separate thread, keeping your ui responsive in this tutorial, we’ll explore how to use isolates in a flutter application to handle heavy data processing tasks, such as deserializing large json files fetched from a back4app backend prerequisites to complete this tutorial, you will need a back4app account sign up for a free account at back4app com https //www back4app com a flutter development environment set up on your local machine follow the flutter installation guide https //flutter dev/docs/get started/install if you haven't set it up yet basic knowledge of dart, flutter widgets, and asynchronous programming step 1 – setting up your back4app backend create a back4app project log in to your back4app account https //www back4app com/ and create a new project create parse classes for this tutorial, create a parse class named record that stores large amounts of data title (string) the title of the record description (string) a description of the record metadata (json) large metadata content associated with the record populate the class with sample data add several records to the record class with large json objects in the metadata field this will simulate the kind of data processing that could cause jank in a real app get your back4app credentials navigate to your project settings to retrieve your application id and client key, which you’ll need to connect your flutter app to back4app step 2 – setting up your flutter project create a new flutter project open your terminal or command prompt and run flutter create isolate example add dependencies open pubspec yaml and add the following dependencies dependencies flutter sdk flutter parse server sdk flutter latest version run flutter pub get to install these dependencies initialize parse in your app in lib/main dart , import the parse sdk and initialize it in the main function import 'package\ flutter/material dart'; import 'package\ parse server sdk flutter/parse server sdk flutter dart'; void main() async { widgetsflutterbinding ensureinitialized(); const keyapplicationid = 'your back4app app id'; const keyclientkey = 'your back4app client key'; const keyparseserverurl = 'https //parseapi back4app com'; await parse() initialize(keyapplicationid, keyparseserverurl, clientkey keyclientkey, autosendsessionid true); runapp(myapp()); } class myapp extends statelesswidget { @override widget build(buildcontext context) { return materialapp( home recordscreen(), ); } } replace 'your back4app app id' and 'your back4app client key' with your actual back4app credentials step 3 – fetching data from back4app create the recordscreen widget in lib/main dart , create a new screen that fetches data from back4app class recordscreen extends statefulwidget { @override recordscreenstate createstate() => recordscreenstate(); } class recordscreenstate extends state\<recordscreen> { list\<parseobject>? records; bool isloading = true; @override void initstate() { super initstate(); fetchrecords(); } future\<void> fetchrecords() async { final query = querybuilder\<parseobject>(parseobject('record')); final response = await query query(); if (response success && response results != null) { setstate(() { records = response results as list\<parseobject>; isloading = false; }); } } @override widget build(buildcontext context) { return scaffold( appbar appbar(title text('records')), body isloading ? center(child circularprogressindicator()) listview\ builder( itemcount records! length, itembuilder (context, index) { final record = records!\[index]; return listtile( title text(record get\<string>('title') ?? 'no title'), subtitle text(record get\<string>('description') ?? 'no description'), ); }, ), ); } } this code fetches all records from the record class in back4app and displays them in a list step 4 – offloading heavy data processing to an isolate using isolate to deserialize large json suppose the metadata field in each record contains a large json object that needs to be deserialized to avoid blocking the ui thread, we'll use an isolate to perform this task import 'dart\ isolate'; import 'dart\ convert'; future\<map\<string, dynamic>> deserializejsoninisolate(string jsonstring) async { // spawning an isolate to perform json decoding final result = await isolate run(() { return jsondecode(jsonstring) as map\<string, dynamic>; }); return result; } future\<void> processrecord(parseobject record) async { string metadata = record get\<string>('metadata') ?? '{}'; // offload json deserialization to an isolate map\<string, dynamic> decodeddata = await deserializejsoninisolate(metadata); // do something with the decoded data print('processed metadata for ${record get\<string>('title')}'); } integrate isolate processing into the app update the recordscreen widget to process each record's metadata using the isolate class recordscreenstate extends state\<recordscreen> { list\<parseobject>? records; bool isloading = true; @override void initstate() { super initstate(); fetchandprocessrecords(); } future\<void> fetchandprocessrecords() async { final query = querybuilder\<parseobject>(parseobject('record')); final response = await query query(); if (response success && response results != null) { list\<parseobject> fetchedrecords = response results as list\<parseobject>; // process each record's metadata using an isolate for (var record in fetchedrecords) { await processrecord(record); } setstate(() { records = fetchedrecords; isloading = false; }); } } @override widget build(buildcontext context) { return scaffold( appbar appbar(title text('records')), body isloading ? center(child circularprogressindicator()) listview\ builder( itemcount records! length, itembuilder (context, index) { final record = records!\[index]; return listtile( title text(record get\<string>('title') ?? 'no title'), subtitle text(record get\<string>('description') ?? 'no description'), ); }, ), ); } } this implementation fetches records from back4app, offloads the heavy json deserialization task to an isolate, and updates the ui once processing is complete step 5 – testing and running your app run your app using flutter run you should see a list of records fetched from back4app the metadata for each record is processed on a separate isolate, ensuring the ui remains smooth and responsive verify performance by testing with large json files in the metadata field observe how the use of isolates prevents jank and keeps the ui responsive conclusion in this tutorial, you learned how to use isolates in flutter to handle heavy data processing tasks, such as deserializing large json files by offloading these tasks to an isolate, you keep the ui thread free to handle rendering, resulting in a smoother and more responsive app integrating back4app as the backend allows you to efficiently manage and retrieve data, while dart’s isolate model ensures that your app remains performant even when handling complex operations for more information on using flutter with back4app, check out the back4app documentation https //www back4app com/docs and flutter documentation https //flutter dev/docs happy coding!