Showing Error (The operator '+' isn't defined for the type 'Uri'. Try defining the operator '+'.dart (undefined_operator))

Question

THIS IS MY CODE this is the app for storing data into google spreadsheets.
// showing red line under plus OPERATOR '+' in LINE

import 'dart:convert' as convert;
import 'package:store_data/models/update.dart';
import 'package:http/http.dart' as http;


class FormController {
  // Callback function to give response of status of current request.
  final void Function(String) callback;

  var url = Uri.parse('https://script.google.com/macros/s/AKfycbzFd5Cw0itASDzFgIrdr97j8PbfWHw1iVcoJWhbChPKfO2c2sA/exec');
  static const STATUS_SUCCESS = "SUCCESS";

  FormController(this.callback);

  void submitForm(Update update) async{
    try{
      await http.get(
        url + update.toParams()).then(
          (response){
            callback(convert.jsonDecode(response.body)['status']);
          });
    } catch(e){
      print(e);
    }
  }
}'

Answer 1

I'm not sure.Try

var url ='...';

then

void submitForm(Update update) async{
url+=update.toParams();
Uri uri = Uri.paste(url);
try{
  await http.get(
    uri).then(
      (response){
        callback(convert.jsonDecode(response.body)['status']);
      });
} catch(e){
  print(e);
}

Answer 2

You can try

var url =
  'https://script.google.com/macros/s/AKfycbzFd5Cw0itASDzFgIrdr97j8PbfWHw1iVcoJWhbChPKfO2c2sA/exec';

static const STATUS_SUCCESS = "SUCCESS";

void submitForm(Update update) async {
try {
  await http.get(Uri.parse(url + update.toParams()).then((response) {
    callback(convert.jsonDecode(response.body)['status']);
  }));
} catch (e) {
  print(e);
}

}