exemplo_flutter_drawer_mediaquery.dart

import 'package:flutter/material.dart';

import 'fragment.dart';

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

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

class MyHomePage extends StatefulWidget {
  final String title;

  const MyHomePage({Key key, this.title}) : super(key: key);

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

class _MyHomePageState extends State<MyHomePage> {
  int _selectedIndex = 0;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: new AppBar(
        title: new Text(widget.title),
      ),
      drawer: Container(
        width: MediaQuery.of(context).size.width*0.65, //Largura de 65% da tela
        child: Drawer(
          child: ListView(
            padding: EdgeInsets.zero,
            children: <Widget>[
              DrawerHeader(
                child: Text('Cabeçalho'),
                decoration: BoxDecoration(
                  color: Colors.blue,
                ),
              ),
              ListTile(
                title: Text('Item 1'),
                selected: 0 == _selectedIndex,
                onTap: () {
                  _onSelectItem(0);
                },
              ),
              ListTile(
                title: Text('Item 2'),
                selected: 1 == _selectedIndex,
                onTap: () {
                  _onSelectItem(1);
                },
              ),
            ],
          ),
        ),
      ),
      body: _getDrawerItem(_selectedIndex),
    );
  }

  _getDrawerItem(int pos) {
    switch (pos) {
      case 0:
        return Fragment("Tela 1");
      case 1:
        return Fragment("Tela 2");
    }
  }

  _onSelectItem(int index) {
    setState(() => _selectedIndex = index);
    Navigator.of(context).pop();
  }
}