title: Flutter: TextFormField, change text
body: <p>I have this future builder that returns a TextFormField:</p>
  
  <pre><code>new FutureBuilder(
                      future: _controller.load(),
                      builder: (BuildContext context, AsyncSnapshot&lt;String&gt; snapshot) {
                      String content;
                      if (snapshot.hasData) {
                      Map data = _controller.decode(snapshot.data);
                      content = data['x'];
                      }
  return TextFormField(controller: 
  textController = new TextEditingController(text: content == null ? "" : content),
  </code></pre>
  
  <p>So, at the beginning, I want that an initial value is shown in the field if the snapshot is not empty. But how can I change this text later? (because, if the user changes this field and then press "ok" on the keyboard, the old value will replace the new one)
  I tried something like:</p>
  
  <pre><code>onFieldSubmitted: (val){
                        setState(() {
                          content = val;
                        });
  </code></pre>
  
  <p>but doesn't work, as soon as I press on "ok", the old value will appear again</p>