title: Flutter - Radio Animation is not showing up on showDialog
body: <p>I'm trying to create a <code>Radio</code> in a <code>showDialog</code>, however the animation that occurs on <code>Radio</code> does not appear in <code>showDialog</code>.</p>
  
  <p>For example: when tapped in <code>foo2</code> nothing happens, and when you exit in <code>showDialog</code> and go back to it, <code>foo2</code> is selected.</p>
  
  <p>Below is the code and a gif showing what is happening:</p>
  
  <p><a href="https://i.stack.imgur.com/o8CaD.gif" rel="noreferrer"><img src="https://i.stack.imgur.com/o8CaD.gif" alt="enter image description here"></a></p>
  
  <pre><code>import "package:flutter/material.dart";
  
  void main() {
    runApp(new ControlleApp());
  }
  
  class ControlleApp extends StatelessWidget {  
    @override
    Widget build(BuildContext context) {
      return new MaterialApp(
        title: "My App",
        home: new HomePage(),
      );
    }
  }
  
  class HomePage extends StatefulWidget {
    @override
    HomePageState createState() =&gt; new HomePageState();
  }
  
  enum _RadioGroup {
    foo1,
    foo2
  }
  
  class HomePageState extends State&lt;HomePage&gt; {
    _RadioGroup _itemType = _RadioGroup.foo1;
  
    void changeItemType(_RadioGroup type) {
      setState(() {
        _itemType = type;
      });
    }
  
    void showDemoDialog&lt;T&gt;({ BuildContext context, Widget child }) {
      showDialog&lt;T&gt;(
        context: context,
        child: child,
      );
    }
  
    @override
    Widget build(BuildContext context){
      return new Scaffold( 
        appBar: new AppBar(backgroundColor: new Color(0xFF26C6DA)),
        body: new Container(
          child: new Row(
            mainAxisAlignment: MainAxisAlignment.center,
            children: &lt;Widget&gt;[
              new InkWell(
                onTap: (){
                  showDemoDialog&lt;String&gt;(
                    context: context,
                    child: new SimpleDialog(
                      title: const Text("show"),
                      children: &lt;Widget&gt;[
                        new Row(
                          mainAxisAlignment: MainAxisAlignment.center,
                          children: &lt;Widget&gt;[
                            new Radio&lt;_RadioGroup&gt;(
                              groupValue: _itemType,
                              value: _RadioGroup.foo1,
                              onChanged: changeItemType
                            ),
                            const Text("foo1"),
  
                            new Radio&lt;_RadioGroup&gt;(
                              groupValue: _itemType,
                              value: _RadioGroup.foo2,
                              onChanged: changeItemType
                            ),
                            const Text("foo2"),
                          ],
                        )
                      ],
                    )
                  );
                },
                child: new Container(
                  margin: new EdgeInsets.only(top: 16.0, bottom: 8.0),
                  child: new Text("Show"),
                ),
              )
            ],
          ),
        )
      );
    }
  }
  </code></pre>