Flutter HTTP Client example with ListView – Fetch data and parse JSON in background

In this tutorial, we’re gonna build a Flutter App that use http package to fetch data from the internet, then parse JSON to a Dart List of Objects and display that List in ListView widget.

Related Post: Flutter ListView example with ListView.builder

Flutter App Overview

We will build a Flutter App that can display a List of Post objects gotten from JSONPlaceholder REST API. We are parsing JSON document that performs an expensive computation in the background.

flutter-http-example-listview-fetch-data-json-background

HTTP Fetch Data in background and Display in ListView

Add http package

Add this package to the dependencies section of our pubspec.yaml:

Create DataModel class

Parse JSON into a List of Objects

We will convert our HTTP Response into a list of Dart objects.

Fetch Data in a separate isolate

This is how we fetch data using the get method:

If we run the fetchPosts() function on a slower phone, the App may freeze for a moment when it parses and converts the JSON.

>> So we are moving the parsing and conversion to a background isolate using Flutter compute() function. This function runs parsePosts() in a background isolate and return the result.

Display the data

In order to display fetched data on screen, we can use the FutureBuilder widget with two parameters:
– The Future to work with. In our case, the return of fetchPosts() function.
– A builder function that tells Flutter what to render, depending on the state of the Future: loading, success, or error.

ListView widget uses ListView.builder:

Practice

Add http package

Add this package to the dependencies section of our pubspec.yaml:

Create DataModel Class

lib/post.dart

Create Main App Widget

lib/main.dart

Create Widget for fetching and parsing data

lib/home.dart

Create ListView Widget

lib/listpost.dart

Source Code

http_example

By grokonez | July 8, 2018.



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5 thoughts on “Flutter HTTP Client example with ListView – Fetch data and parse JSON in background”

  1. thanks for this article, helped me get started with my project.
    One think that I ran into and could not figure out was how to add http client timeout and show message for it.
    Is that something you have an example of ?

    1. Hi Peder,

      We have 2 ways to set Timeout for HTTP Request:
      – use Future.timeout() method:

      – use HttpClient.connectionTimeout() method => apply to all requests made by the same client. When a request exceeds this timeout, a SocketException is thrown:

      Regards,
      grokonez.

  2. First of all your tutorials are great learning source. Specially flutter.

    Regarding this tutorial, how can we add pagination call in this code with scrollcontroller so that when scroll reach to end then we can pass next url.

    You are doing great work.

    Thanks

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