How to post JSON array in Flutter

Question

I want to send data to my API URL. How to post below JSON array?

The data I want to send is this:

  requests: [
            {
                OptionID: [
                {
                    ID: 'A1'
                }
                ],
                content: {
                img: 'image'
                }
            }
            ]

Here is my code:

var data = "requests: [{ OptionID: [ {ID: 'A1'}], content: { img: 'image'}}]";
http.Response response = await http.post("https://MY_API_URL", body: data);
print(response.body);

Now I have an error about Invalid Argument because I don't know how to send a JSON array.

Can anyone help me?

mkrieger1 · Accepted Answer · 2020-03-31 16:14:49Z

1

Your data string does not follow a JSON syntax.

JSON syntax is:

Data is in name/value pairs
Data is separated by commas
Curly braces hold objects
Square brackets hold arrays
field name must be in double quotes

For example:

var data = '{ "requests": [{"OptionID": [{ "ID": "A1"} ],"content": {"img": "image" }}]}';

You should compose your string in this way or you can create an object as well and then using json.encode(data) for creating the right string.

For example:

var data = {
     "requests": [
    {
        "OptionID": [
          {
            "ID": "A1"
          }
        ],
        "content": {
          "img": "image"
        }
    }
    ]
}

json.encode(data)

edited Mar 31, 2020 at 16:14

mkrieger1

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answered Mar 31, 2020 at 15:03

mraf4

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2 Comments

qing Over a year ago

thank you, it work. But why we sometime need to put json.encode(data) sometime no need?

mraf4 Over a year ago

json.encode(data) parse your object to a string value, so when you have an object you have to use it to convert object into a string. When you have already a string value as json syntax, you don't need to parse it using json.encode

SaltH2OFish · Accepted Answer · 2020-04-01 19:26:11Z

1

The body parameter should be a Map. Since you have your json data in a var (String) it needs to be converted to a Map. You can do this:

//you'll need jsonEncode and that is part of dart:convert

import 'dart:convert';


//Since you have data inside of "" it is a String.  If you defined this as a Map<String, dynamic> and created this as a map, you wont need to convert.

var data = "requests: [{ OptionID: [ {ID: 'A1'}], content: { img: 'image'}}]";


//use jsonEncode with your data here

http.Response response = await http.post("https://MY_API_URL", body: jsonEncode(data));

print(response.body);

edited Apr 1, 2020 at 19:26

answered Mar 31, 2020 at 15:00

SaltH2OFish

2202 silver badges8 bronze badges

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