SetState example not rerendering after each statement

main.dart

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      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();
}

enum MyState { initial, loading, success, error }

class _MyHomePageState extends State<MyHomePage> {
  MyState _currentState = MyState.initial;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(child: _buildBody()),
      floatingActionButton: FloatingActionButton(
        onPressed: _updateState,
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }

  void _updateState() {
    setState(() {
      _currentState = MyState.initial;
    });

    setState(() {
      _currentState = MyState.loading;
    });

    setState(() {
      _currentState = MyState.success;
    });
  }

  Widget _buildBody() {
    switch (_currentState) {
      case MyState.loading:
        return CircularProgressIndicator();
      case MyState.error:
        return Text("error");
      case MyState.success:
        return Text("success");
      case MyState.initial:
      default:
        return Text("Initial State");
    }
  }
}