title: how to change showDatePicker input format flutter
body: <p>I'm using showDatePicker function to pick a date from the dialog Calendar. It shows an edit icon at the top right (see img 1) to change to input mode  where the user can enter the date as a text (see img 2)
  The problem is with the input format, I want that text editor input follow this format yyyy-mm-dd. The problem is that in the begning it show me the date like yyyy-mm-dd, but when the I try to remove the first number it changes automaticly to this format mm/dd/yyyy. </p>
  
  <p>How to set the input format to  yyyy-mm-dd. If showDatePicker dont support that with the swedish language, so how to hide the edit icon for ever from the top right. Help me thanks</p>
  
  <p><a href="https://i.stack.imgur.com/xEfBM.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/xEfBM.png" alt="img 1"></a>
  img 1</p>
  
  <p><a href="https://i.stack.imgur.com/HPiBO.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/HPiBO.png" alt="img 2"></a>
  img 2</p>
  
  <p>Here is my code     </p>
  
  <pre><code>  DateTime selectedDate = DateTime.now();
    String date = DateFormat("yyyy-MM-dd").format(DateTime.now()); 
  ...
  FlatButton(
           onPressed: ()async {
  
             final DateTime picked = await showDatePicker(
                 locale: const Locale('sv'), // Swedish calander
                 context: context,
                 initialDate: selectedDate,
                 firstDate: DateTime(1970, 8),
                 lastDate: DateTime(2101));
  
             if (picked != null &amp;&amp; picked != selectedDate) {
               setState(() {
                 selectedDate = picked;
                 String Onlydate = new DateFormat("yyyy-MM-dd").format(picked); 
  
                 date = '$Onlydate';
  
  
               });
             }
           },
           child: Row(
             children: &lt;Widget&gt;[
               Text(' * $date'),
             ],
           ),
         );`
  </code></pre>