JSON (JavaScript Object Notation) is a lightweight data-interchange format that is easy for humans to read and write and easy for machines to parse and generate. In Flutter, the dart:convert library provides the JsonDecoder and JsonEncoder classes, which can be used to convert between JSON strings and Dart objects.
By default, the JsonDecoder class is strict when parsing JSON strings. This means that it will throw a FormatException if the JSON string is malformed or contains syntax errors. However, there may be situations where you want to parse a JSON string even if it is malformed or contains syntax errors. For example, you may be working with a third-party API that occasionally returns malformed JSON.
The JsonDecoder class provides a lenient property that can be set to true to allow the decoder to parse malformed JSON. When lenient is set to true, the decoder will ignore any syntax errors and return the best representation of the JSON that it can. Here is an example of how to use the JsonDecoder class with lenient set to true:
import 'dart:convert';
String jsonString = '{"name":"John", "age":30, "city":"New York"}';
var jsonDecoder = JsonDecoder(lenient: true);
var jsonMap = jsonDecoder.convert(jsonString);
print(jsonMap);
In this example, the jsonDecoder variable is an instance of the JsonDecoder class with lenient set to true. The convert method is called on the jsonDecoder variable with the jsonString variable as its argument. The convert method returns a Map<String, dynamic> object that contains the key-value pairs of the JSON string.
If the jsonString is malformed or contains syntax errors, the decoder will return the best representation of the JSON that it can and print it
You should also be aware that when using lenient mode, the decoder may return unexpected results when parsing malformed JSON. It is recommended to use lenient mode only as a last resort, when you have no other option but to parse a malformed JSON string.
In a nutshell, if you want to accept malformed JSON in Flutter, you can use the JsonDecoder class with the lenient property set to true. This allows you to parse a JSON string even if it is malformed or contains syntax errors.
Another important aspect of working with JSON in Flutter is encoding and decoding JSON strings. The JsonEncoder class provides a convert method that can be used to convert a Dart object to a JSON string. Here's an example of how to use the JsonEncoder class:
import 'dart:convert';
Map<String, dynamic> jsonMap = {
"name": "John",
"age": 30,
"city": "New York"
};
var jsonEncoder = JsonEncoder.withIndent(' ');
String jsonString = jsonEncoder.convert(jsonMap);
print(jsonString);
In this example, the jsonEncoder variable is an instance of the JsonEncoder class. The convert method is called on the jsonEncoder variable with the jsonMap variable as its argument. The convert method returns a JSON string that represents the key-value pairs of the jsonMap object.
Additionally, it's also possible to use the jsonEncode function as a shorthand to encode a dart object to json string.
import 'dart:convert';
Map<String, dynamic> jsonMap = {
"name": "John",
"age": 30,
"city": "New York"
};
String jsonString = jsonEncode(jsonMap);
print(jsonString);
It's also possible to customize the encoding process by passing an instance of JsonEncoder to the jsonEncode function.
Another related topic is handling JSON null values. By default, the JsonDecoder class will convert JSON null values to null in Dart. But, if you want to handle null values differently, you can use the JsonDecoder.withReviver method. The withReviver method takes a function that is called for every key-value pair in the JSON string. The function can then decide how to handle the value. For example, you can use the withReviver method to convert JSON null values to an empty string:
import 'dart:convert';
String jsonString = '{"name":"John", "age":null, "city":"New York"}';
var jsonDecoder = JsonDecoder.withReviver((key, value) {
if (value == null) {
return '';
}
return value;
});
var jsonMap = jsonDecoder.convert(jsonString);
print(jsonMap);
In this example, the jsonDecoder variable is an instance of the JsonDecoder class with a custom withReviver function. The function checks if the value is null and returns an empty string if it is. The convert method is called on the jsonDecoder variable with the jsonString variable as its argument. The convert method returns a Map<String, dynamic> object that contains the key-value pairs of the JSON string, with all null values replaced with empty strings.
In conclusion, working with JSON in Flutter can be done using the dart:convert library's JsonDecoder, JsonEncoder classes and jsonEncode function. It
Popular questions
Q: What is JSON?
A: JSON (JavaScript Object Notation) is a lightweight data-interchange format that is easy for humans to read and write and easy for machines to parse and generate.
Q: How can I parse a malformed JSON string in Flutter?
A: In Flutter, you can use the JsonDecoder class with the lenient property set to true to parse a malformed JSON string. This allows the decoder to ignore any syntax errors and return the best representation of the JSON that it can.
Q: How can I encode a Dart object to a JSON string in Flutter?
A: You can use the JsonEncoder class's convert method or the jsonEncode function to encode a Dart object to a JSON string.
Q: How can I handle JSON null values in Flutter?
A: You can use the JsonDecoder.withReviver method to handle JSON null values differently. The withReviver method takes a function that is called for every key-value pair in the JSON string, and you can use this function to decide how to handle the value.
Q: What should I keep in mind when using the lenient property in JsonDecoder?
A: When using the lenient property in JsonDecoder to parse malformed JSON, the decoder may return unexpected results. It is recommended to use lenient mode only as a last resort, when you have no other option but to parse a malformed JSON string.
Tag
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