Search change state

search_change_state.dart

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      debugShowCheckedModeBanner: false,
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  String _pesquisa = '';
  bool _isLoading = false;

  _pesquisarPor(String textoPesquisa)  {
    setState(()  {
      _pesquisa = textoPesquisa;
    });
  }
  
  _setIsLoading(){
    setState(()  {
      _isLoading = !_isLoading;
    });    
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.start,
          children: <Widget>[
            _isLoading
                ? CircularProgressIndicator()
                : Text('Lista Carregada!'),
            Container(
              child: TextField(
                onChanged: (value) {
                  _setIsLoading();
                   _pesquisarPor(value);
                  Future.delayed(Duration(seconds: 2), () {
                    _setIsLoading();
                  });
                },
                decoration: InputDecoration(
                  enabledBorder: InputBorder.none,
                  focusedBorder: InputBorder.none,
                  hintText: "Search...",
                  prefixIcon: Icon(Icons.search),
                ),
              ),
            ),
            Text(
              'Pesquisando por:',
            ),
            Text(
              '$_pesquisa',
              style: Theme.of(context).textTheme.headline4,
            ),
          ],
        ),
      ),
    );
  }
}