Convert List into json in flutter

Question

I have a list of option when the attribute is selected of a particular option then I save attribute object at the selected position of option in the list. now I have an option list with their selected attribute object. My aim is to convert the options list into JSON object but when the attribute is not null. The Attribute object can be null in that case when a person has not chosen an attribute of an option.

class OptionAttribute{
 String _grouprowid;
 String _groupname;
 Attribute _selectedAttrObject

   Map<String, dynamic> toJson() => {
    'attribute': _selectedAttrObject,
  };
}

class Attribute{

  String _attributerowid;
  String _grouprowid;
  String _attributename;
  String _weight;

   Map<String, dynamic> toJsonAttr() => {
    'attrid': _attributerowid,
    'groupid': _grouprowid,
    'attrname': _attributename
  };

}

I want to convert below list into JSON object when the list does not have any null attribute.

List<OptionAttribute> opAtrrList=new List<OptionAttribute>();

Günter Zöchbauer · Accepted Answer · 2019-03-08T07:29:44.183

59

You need to convert each item individually

var json = jsonEncode(opAttrList.map((e) => e.toJson()).toList());

or pass an toEncodable function

var json = jsonEncode(opAttrList, toEncodable: (e) => e.toJsonAttr());

edited Mar 08 '19 at 07:29

answered Mar 08 '19 at 06:55

Günter Zöchbauer

623,577
216
2,003
1,567

1

showing error of `Instance of 'MappedListIterable>` where I'm doing wrong – Farhana Naaz Ansari Mar 08 '19 at 07:25
`'attribute': _selectedAttrObject,` should be `'attribute': _selectedAttrObject.toJsonAttr(),` – Günter Zöchbauer Mar 08 '19 at 07:29
now it is showing error `Converting object to an encodable object failed: Instance of 'Attribute'` – Farhana Naaz Ansari Mar 08 '19 at 07:29
(unrelated to the errors you mentioned) You should name `toJson()` the same on all classes. For example there is no point in adding `Attr` to `toJson()`. – Günter Zöchbauer Mar 08 '19 at 07:30
Gunter almost done, but how can i handle if `attribute` is not selected in that case it is showing error **The method 'toJson' was called on null.** – Farhana Naaz Ansari Mar 08 '19 at 07:36
1

Adding `?` might do `'attribute': _selectedAttrObject?.toJson(),` or if you want `'attribute': null` removed as well, use `Map toJson() => _selectedAttrObject != null ? { 'attribute': _selectedAttrObject, } : {};` – Günter Zöchbauer Mar 08 '19 at 07:38
1

Glad to hear :) – Günter Zöchbauer Mar 08 '19 at 07:45

Convert List into json in flutter

1 Answers1

Linked