Flutter : How to add more json data to existing Model Class? - flutter

Question

I have a scenario where the following function is called again and again whenever the user hits the "Load More" button.
The problem I'm facing is, that it replaces previously loaded data with a new one. Instead, it should add to the bottom of the Listview.Builder
Future fetchData() async{
var url = "url_goes_here";
final response = await http.get(url);
if (response.statusCode == 200) {
var resBody = jsonDecode(response.body);
var data = resBody['data'] as List;
if (data.isNotEmpty) {
setState(() {
listVariable = data
.map<ModelClass>((json) => ModelClass.fromJson(json))
.toList();
});
}
}
}

Answer 1

List<ModelClass> listVariable =List<ModelClass>(); //describe the object that way.
--------and---------
data.map<ModelClass>((json) {
listVariable.add(ModelClass.fromJson(jsonn));
} )).toList();

Answer 2

You should add received data to your listVariable, not assign a new value. Try this code:
final listVariable = <ModelClass>[];
...
Future fetchData() async {
var url = "url_goes_here";
final response = await http.get(url);
if (response.statusCode == 200) {
var resBody = jsonDecode(response.body);
var data = resBody['data'] as List;
if (data.isNotEmpty) {
final list = data.map<ModelClass>((json) => ModelClass.fromJson(json));
setState(() {
listVariable.addAll(list); // HERE: addAll() instead of assignment
});
}
}
}

Answer 3

I was able to figure out answer myself.
setState(() {
listVariable.addAll(data
.map<ModelClass>((json) => ModelClass.fromJson(json))
.toList();
}));
#Mol0ko and #hasan karaman both are right but #Mol0ko
Makes better sense when you have a set of data to addAll to existing data.