How to add dynamically items to the table in flutter?

You can use

listOfColumns.map(((element) => DataRow(...))).toList()

This is your code using this method.

class DataTableWidget extends StatelessWidget {
  final List<Map<String, String>> listOfColumns = [
    {"Name": "AAAAAA", "Number": "1", "State": "Yes"},
    {"Name": "BBBBBB", "Number": "2", "State": "no"},
    {"Name": "CCCCCC", "Number": "3", "State": "Yes"}
  ];
//  DataTableWidget(this.listOfColumns);     // Getting the data from outside, on initialization
  @override
  Widget build(BuildContext context) {
    return DataTable(
      columns: [
        DataColumn(label: Text('Patch')),
        DataColumn(label: Text('Version')),
        DataColumn(label: Text('Ready')),
      ],
      rows:
          listOfColumns // Loops through dataColumnText, each iteration assigning the value to element
              .map(
                ((element) => DataRow(
                      cells: <DataCell>[
                        DataCell(Text(element["Name"])), //Extracting from Map element the value
                        DataCell(Text(element["Number"])),
                        DataCell(Text(element["State"])),
                      ],
                    )),
              )
              .toList(),
    );
  }
}

You could do something like this:**

class DataTableWidget extends StatelessWidget {

      List results=[] ;
       intState((){
         super.iniState();
            this.getSale();
 })
Future<String> getData () async {

var response = await http.get(
  "$saleUrl/?format=json",

);
setState(() {
  var dataConvertedToJson = 
json.decode(utf8.decode(response.bodyBytes));
  results = dataConvertedToJson['results'];
});
 print('${results.length}');
  return "successful";
 }
  DataRow _getDataRow(result) {
    return DataRow(
      cells: <DataCell>[
        DataCell(Text(data["text1"])),
        DataCell(Text(data["text2"])),
        DataCell(Text(data["text3"])),
      ],
    );
  }

  @override
  Widget build(BuildContext context) {
    return DataTable(
      columns: [
        DataColumn(label: Text('Patch')),
        DataColumn(label: Text('Version')),
        DataColumn(label: Text('Ready')),
      ],
      rows: List.generate(
          results.length, (index) => _getDataRow(results[index])),
    );
  }
}

The underlying data structure, probably a list, is what you want to worry about changing. UI elements like the table just observe. The setState() function notifies the UI to take a fresh look after you've updated your list.

Here's a working example hacked from a flutter doc example. Click the button to add rows.

import 'package:flutter/material.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Add Rows',
      home: MyHomePage(title: 'Add Rows'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);
  final String title;
  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  List<DataRow> _rowList = [
    DataRow(cells: <DataCell>[
      DataCell(Text('AAAAAA')),
      DataCell(Text('1')),
      DataCell(Text('Yes')),
    ]),
  ];

  void _addRow() {
    // Built in Flutter Method.
    setState(() {
      // This call to setState tells the Flutter framework that something has
      // changed in this State, which causes it to rerun the build method below.
      _rowList.add(DataRow(cells: <DataCell>[
        DataCell(Text('BBBBBB')),
        DataCell(Text('2')),
        DataCell(Text('No')),
      ]));
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: DataTable(columns: [
          DataColumn(label: Text('Patch')),
          DataColumn(label: Text('Version')),
          DataColumn(label: Text('Ready')),
        ], rows: _rowList),
      ),
      floatingActionButton: FloatingActionButton.extended(
        onPressed: _addRow,
        label: Text('Add Row'),
        backgroundColor: Colors.green,
      ),
    );
  }
}

This builds for me with

flutter build web

then run with

flutter run -d chrome