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Pro đang tìm kiếm từ khóa Convert List Object to JSON java được Update vào lúc : 2022-12-05 00:55:06 . Với phương châm chia sẻ Bí quyết về trong nội dung bài viết một cách Chi Tiết 2022. Nếu sau khi đọc tài liệu vẫn ko hiểu thì hoàn toàn có thể lại Comments ở cuối bài để Mình lý giải và hướng dẫn lại nha.

In this Dart/Flutter JSON encode tutorial, I will show you ways to convert Object, Nested Object, List, List of JSON objects into JSON string. Finally, you can convert a complex Nested Object (that contains some fields and a List of objects field) into JSON string.

Nội dung chính

Dart/Flutter convert simple Object to JSON stringDart/Flutter convert Nested Object to JSON stringDart/Flutter convert List to JSON stringDart/Flutter convert List of objects to JSON stringDart/Flutter convert complex Nested Object to JSON stringFurther ReadingVideo liên quan

Related Posts:
Dart/Flutter Convert/Parse JSON string, array into Object, List
Dart/Flutter Constructors tutorial with examples
Dart/Flutter String Methods & Operators tutorial with examples
Dart/Flutter Future Tutorial with Examples
Dart/Flutter List Tutorial with Examples
Dart/Flutter Map Tutorial with Examples

Contents

OverviewDart/Flutter convert simple Object to JSON stringDart/Flutter convert Nested Object to JSON stringDart/Flutter convert List to JSON stringDart/Flutter convert List of objects to JSON stringDart/Flutter convert complex Nested Object to JSON stringConclusionFurther Reading

Overview

dart:convert library provides a built-in top-level function called jsonEncode that can convert many types of Object to JSON string.

We have 3 steps to convert an Object/List to JSON string:

create the classcreate toJson() method which returns a JSON object that has key/value pairs corresponding to all fields of the classget JSON string from JSON object/List using jsonEncode() function

For every type of Object, Nested Object, simple List, List of Objects, or Nested Object containing List, we will implement toJson() method with some little difference.

Dart/Flutter convert simple Object to JSON string

Assume that we have a User class with fields: name & age.

class User

String name;

int age;

User(this.name, this.age);

If you call jsonEncode() function without creating toJson() method. You will get an error:

Unhandled exception:

Converting object to an encodable object failed: Instance of ‘User’

…

Lets create toJson() method like the following code:

class User

String name;

int age;

User(this.name, this.age);

Map toJson() =>

‘name’: name,

‘age’: age,

;

Now we can use dart:convert librarys built-in jsonEncode() function to convert the User object to JSON string:

import ‘dart:convert’;

main()

User user = User(‘bezkoder’, 21);

String jsonUser = jsonEncode(user);

print(jsonUser);

The result will show a string like this.

“name”:”bezkoder”,”age”:21

Dart/Flutter convert Nested Object to JSON string

If we have a Tutorial class and author is a field that has User class type.
Were gonna create toJson() method with the author is the result when calling Users toJson() method.

class User

String name;

int age;

…

class Tutorial

String title;

String description;

User author;

Tutorial(this.title, this.description, [this.author]);

Map toJson()

Map author =

this.author != null ? this.author.toJson() : null;

return ‘title’: title, ‘description’: description, ‘author’: author;

Remember to check if author property is null or not.
Now we can easily call jsonEncode() like this.

import ‘dart:convert’;

main()

User user = User(‘bezkoder’, 21);

Tutorial tutorial = Tutorial(‘Dart Tut#1’, ‘Tut#1 Description’, user);

String jsonTutorial = jsonEncode(tutorial);

print(jsonTutorial);

Check the result, you can see our JSON string:

“title”:”Dart Tut#1″,”description”:”Tut#1 Description”,”author”:”name”:”bezkoder”,”age”:21

Dart/Flutter convert List to JSON string

We can easily do JSON encode a List without the need of creating any class.

import ‘dart:convert’;

main()

List<String> tags = [‘tagA’, ‘tagB’, ‘tagC’];

String jsonTags = jsonEncode(tags);

print(jsonTags);

The result shows a JSON string array:

[“tagA”,”tagB”,”tagC”]

Dart/Flutter convert List of objects to JSON string

How about more complicated List? For example, every item in the List is a Tag object.
The Tag class has 2 fields: name & quantity. So we also need to create toJson() method that return a Map.

class Tag

String name;

int quantity;

Tag(this.name, this.quantity);

Map toJson() =>

‘name’: name,

‘quantity’: quantity,

;

Now everything becomes simple with jsonEncode() function.

import ‘dart:convert’;

main()

List<Tag> tags = [Tag(‘tagA’, 3), Tag(‘tagB’, 6), Tag(‘tagC’, 8)];

String jsonTags = jsonEncode(tags);

print(jsonTags);

JSON string looks like an array:

[“name”:”tagA”,”quantity”:3,”name”:”tagB”,”quantity”:6,”name”:”tagC”,”quantity”:8]

Dart/Flutter convert complex Nested Object to JSON string

Yeah! Youre in the last section of this tutorial.
We will convert a complex Nested Object that contains some fields and a List of objects field into JSON string.

For example, Tutorial class has title, description, author (User class), tags (List<Tag>):

class Tutorial

String title;

String description;

User author;

List<Tag> tags;

Tutorial(this.title, this.description, [this.author, this.tags]);

Were gonna define the toJson() method like this:

class Tutorial

…

Map toJson()

Map author =

this.author != null ? this.author.toJson() : null;

List<Map> tags =

this.tags != null ? this.tags.map((i) => i.toJson()).toList() : null;

return

‘title’: title,

‘description’: description,

‘author’: author,

‘tags’: tags

;

In the constructor method, we set author and tags optional.
So when initializing a Tutorial, we dont need to pass these fields as parameters.

We use map on tags property to return the JSON object. Then, convert the map result to a List of JSON object using toList() method.

Our main() function will be like this.

import ‘dart:convert’;

main()

User user = User(‘bezkoder’, 21);

String jsonUser = jsonEncode(user);

print(jsonUser);

List<Tag> tags = [Tag(‘tagA’, 3), Tag(‘tagB’, 6), Tag(‘tagC’, 8)];

String jsonTags = jsonEncode(tags);

print(jsonTags);

Tutorial tutorial = Tutorial(‘Dart Tut#2’, ‘Tut#2 Description’, user, tags);

String jsonTutorial = jsonEncode(tutorial);

print(jsonTutorial);

Lets check the result in console, you will see the JSON string.

“title”:”Dart Tut#2″,”description”:”Tut#2 Description”,”author”:”name”:”bezkoder”,”age”:21,”tags”:[“name”:”tagA”,”quantity”:3,”name”:”tagB”,”quantity”:6,”name”:”tagC”,”quantity”:8]

If we dont initialize Tutorial with author and tags as the following code.

import ‘dart:convert’;

main()

Tutorial tutorial = Tutorial(‘Dart Tut#3’, ‘Tut#3 Description’);

String jsonTutorial = jsonEncode(tutorial);

print(jsonTutorial);

This is the result:

“title”:”Dart Tut#3″,”description”:”Tut#3 Description”,”author”:null,”tags”:null

Conclusion

Thats how we convert many kind of Objects and List to JSON string in Dart/Flutter. One of the most important part to make our work simple is the dart:convert librarys built-in jsonEncode() function.

You can find way to convert in the opposite way :
Dart/Flutter Convert/Parse JSON string, array into Object, List

Happy Learning! See you again.

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Table of Content

Convert List Object to JSON java Mới nhất

Mẹo về Convert List Object to JSON java Mới Nhất

Overview

Dart/Flutter convert simple Object to JSON string

Dart/Flutter convert Nested Object to JSON string

Dart/Flutter convert List to JSON string

Dart/Flutter convert List of objects to JSON string

Dart/Flutter convert complex Nested Object to JSON string

Conclusion

Further Reading

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