title: Prevent dialog from closing on outside touch in Flutter
body: <p>In Flutter i write simple dialog for loader during async task. when i touch outside dialog dismissed, How can I stop this behaviour ?</p>
  
  <p><strong>Code</strong></p>
  
  <pre><code>  showDialog(
      context: context,
      builder: (_) =&gt; new Dialog(
            child: new Container(
              alignment: FractionalOffset.center,
              height: 80.0,
              padding: const EdgeInsets.all(20.0),
              child: new Row(
                mainAxisSize: MainAxisSize.min,
                children: [
                  new CircularProgressIndicator(),
                  new Padding(
                    padding: new EdgeInsets.only(left: 10.0),
                    child: new Text("Loading"),
                  ),
                ],
              ),
            ),
          ));
  </code></pre>
  
  <p>Any help will be appreciated, thank you in advance.</p>