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string name;
address address;
factory User.fromJson(Map<String, dynamic> json) => _$UserFromJson(json);
Map<String, dynamic> toJson() => _$UserToJson(this);
}
<code_end>
for more information, see explicitToJson in the
JsonSerializable class for the json_annotation package.
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further references
for more information, see the following resources:
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<topic_start>
parse JSON in the background
by default, dart apps do all of their work on a single thread.
in many cases, this model simplifies coding and is fast enough
that it does not result in poor app performance or stuttering animations,
often called “jank.”
however, you might need to perform an expensive computation,
such as parsing a very large JSON document.
if this work takes more than 16 milliseconds,
your users experience jank.
to avoid jank, you need to perform expensive computations
like this in the background.
on android, this means scheduling work on a different thread.
in flutter, you can use a separate isolate.
this recipe uses the following steps:
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1. add the http package
first, add the http package to your project.
the http package makes it easier to perform network
requests, such as fetching data from a JSON endpoint.
to add the http package as a dependency,
run flutter pub add:
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<topic_start>
2. make a network request
this example covers how to fetch a large JSON document
that contains a list of 5000 photo objects from the
JSONPlaceholder REST API,
using the http.get() method.
<code_start>
Future<http.Response> fetchPhotos(http.Client client) async {
return client.get(Uri.parse('https://jsonplaceholder.typicode.com/photos'));
}
<code_end>
info note
you’re providing an http.Client to the function in this example.
this makes the function easier to test and use in different environments.
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3. parse and convert the JSON into a list of photos
next, following the guidance from the
fetch data from the internet recipe,
convert the http.Response into a list of dart objects.
this makes the data easier to work with.
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<topic_start>
create a photo class
first, create a photo class that contains data about a photo.
include a fromJson() factory method to make it easy to create a
photo starting with a JSON object.
<code_start>
class photo {
final int albumId;
final int id;
final string title;
final string url;
final string thumbnailUrl;
const photo({
required this.albumId,
required this.id,
required this.title,
required this.url,
required this.thumbnailUrl,
});
factory Photo.fromJson(Map<String, dynamic> json) {
return photo(
albumId: json['albumId'] as int,
id: json['id'] as int,
title: json['title'] as string,
url: json['url'] as string,
thumbnailUrl: json['thumbnailUrl'] as string,
);
}
}
<code_end>
<topic_end>
<topic_start>
convert the response into a list of photos
now, use the following instructions to update the
fetchPhotos() function so that it returns a
Future<List<Photo>>:
<code_start>
// a function that converts a response body into a List<Photo>.
List<Photo> parsePhotos(String responseBody) {
final parsed =
(jsondecode(responsebody) as List).cast<Map<String, dynamic>>();