title: Issues with Dropdown button in flutter
body: <p>I am having issues getting a Dropdownbutton widget working in flutter (1.0), it is constantly throwing errors,</p>
  
  <p>following is my code:</p>
  
  <pre><code>import 'package:flutter/material.dart';
  
  void main() =&gt; runApp(new Myapp());
  
  class Myapp extends StatefulWidget {
    @override
    State&lt;StatefulWidget&gt; createState() {
      return new Myappstate();
    }
  }
  
  class Myappstate extends State&lt;Myapp&gt; {
    String value = '';
    List&lt;String&gt; values = [];
    void init() {
      values.addAll(['one', 'two']);
      value = values.elementAt(0);
    }
  
    Widget build(BuildContext context) {
      return new Scaffold(
        appBar: new AppBar(
          title: new Text("drop down demo"),
        ),
        body: new Container(
          child: new Column(
            children: &lt;Widget&gt;[
              new DropdownButton(
                items: values.map((String val) {
                  return new DropdownMenuItem(
                    value: val,
                    child: Text(val),
                  );
                }).toList(),
                onChanged: null,
              )
            ],
          ),
        ),
      );
    }
  }
  </code></pre>
  
  <p>I recieve following error :</p>
  
  <pre><code>Launching lib\main.dart on Android SDK built for x86 in debug mode...
  Built build\app\outputs\apk\debug\app-debug.apk.
  I/flutter ( 4352): ══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞═══════════════════════════════════════════════════════════
  I/flutter ( 4352): The following assertion was thrown building Myapp(state: Myappstate#1abe5):
  I/flutter ( 4352): MediaQuery.of() called with a context that does not contain a MediaQuery.
  I/flutter ( 4352): No MediaQuery ancestor could be found starting from the context that was passed to MediaQuery.of().
  I/flutter ( 4352): This can happen because you do not have a WidgetsApp or MaterialApp widget (those widgets introduce
  I/flutter ( 4352): a MediaQuery), or it can happen if the context you use comes from a widget above those widgets.
  I/flutter ( 4352): The context used was:
  I/flutter ( 4352):   Scaffold(dirty, state: ScaffoldState#cda06(lifecycle state: initialized, tickers: tracking 1
  I/flutter ( 4352):   ticker))
  </code></pre>
  
  <p>I am trying to add this very basic widget but for some reason i have not been able to find the problem.</p>
  
  <p>appreaciate any help i can find.</p>