FutureBuilder

main.dart

// Copyright 2015 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

import 'dart:async';

import 'package:flutter/material.dart';
import 'package:flutter/widgets.dart';

void main() {
  runApp(new MaterialApp(home: new NewTransactionPage()));
}

class NewTransactionPage extends StatefulWidget {
  @override
  State createState() => new _NewTransactionPageState();
}

class _NewTransactionPageState extends State<NewTransactionPage> {
  @override
  Widget build(BuildContext context) {
    final Future<Null> futureParticipants = new Future<Null>.delayed(new Duration(seconds: 2));

    return new Scaffold(
      appBar: new AppBar(
        title: const Text('Add transaction'),
      ),
      body: new FutureBuilder<Null>(
        future: futureParticipants,
        builder: (BuildContext context, AsyncSnapshot<List<Map>> snapshot) {
          if (snapshot.connectionState != ConnectionState.done)
            return const Text('Loading...');

          return
            new DropdownButton<int>(
              items: [1, 2, 3]
                  .map((int row) => new DropdownMenuItem<int>(
                  value: row,
                  child: const Text('lol')))
                  .toList(),
              onChanged: (int value) {
                print('selected $value');
              },
            );
        },
      ),
    );
  }
}