title: setState resets Datepicker and do not change the text
body: <p>I am trying to change the value of a text with a button, but I got 2 problems:
  1- setState resets the date 
  2- The text do not change </p>
  
  <p><em>Edited</em>
  Here I post the code:</p>
  
  <pre><code>class MyHomePage extends StatefulWidget {
    MyHomePage({Key key, this.title}) : super(key: key);
    final String title;
    @override
    _MyHomePageState createState() =&gt; _MyHomePageState();}
  
  class _MyHomePageState extends State&lt;MyHomePage&gt; {
    @override
    Widget build(BuildContext context) {
  
  TextEditingController dateCtl = TextEditingController();
  String operad = "Operador";
  DateTime date;
  var formatter = new DateFormat('dd-MM-yyyy');
  
      return Scaffold(appBar: AppBar(title: Text(widget.title),),
        body: Center(child: Column(mainAxisAlignment: MainAxisAlignment.start,
            children: &lt;Widget&gt;[
            Row(mainAxisAlignment: MainAxisAlignment.center,children: &lt;Widget&gt;[
            SizedBox(height: 35,width: 100,
            child:Text('Fecha:',style: TextStyle(fontSize: 18.0),textAlign: TextAlign.end,)),
            SizedBox(height: 35,width: 250,
            child:
            TextFormField(
              readOnly: true,
              textAlign: TextAlign.center,
              controller: dateCtl,
              onTap: () async{date = await showDatePicker(
                                         context: context,
                                        initialDate: DateTime.now(),
                                        firstDate: DateTime.now().subtract(Duration(days: 2)),
                                        lastDate: DateTime.now().add(Duration(days: 2)));
                  if (date == null) {
                    date = DateTime.now();
                  } else {
                    dateCtl.text = formatter.format(date);}}))]),
  Row(mainAxisAlignment: MainAxisAlignment.center,
  children: &lt;Widget&gt;[
  SizedBox(width: 95, height: 40,
  child: RaisedButton(
  
            child: Text("A. Pacho",style: TextStyle(color:Color.fromRGBO(255, 255, 255, 5),fontSize: 16, fontStyle: FontStyle.italic),textAlign: TextAlign.center),
            color: Color.fromRGBO(16, 172, 40,80),
            padding: EdgeInsets.only(left:2, right:1.5),
            highlightColor: Color.fromRGBO(230, 17, 17, 10),
            elevation: 5.0,
            shape: RoundedRectangleBorder(
                   borderRadius: new BorderRadius.circular(15.0)),
            onPressed: () {
                  setState(() {
                    operad = "Adolfo Pacho";
                  });},)),]),
  
  Row(mainAxisAlignment: MainAxisAlignment.center,
    children: &lt;Widget&gt;[
  SizedBox(width: 160, height: 30,child:Text('$operad')),
  SizedBox(width: 15,),
  ],),
  </code></pre>
  
  <p>What I need to do is:
  When I pressed the RaisedButton, the text inside the Sizedbox must change.</p>
  
  <p>What it does:
  When I pressed the RaisedButton, the text inside the Sizedbox does not change and the Datepicker resets.</p>
  
  <p>:(</p>