title: Flutter Text will not update further after Textfield input
body: <blockquote>
    <p>I have arrow buttons to increase or decrease a variable <code>age</code> which work fine to update the <code>hintText</code>, but if I use the <code>TextField</code> widget to input a new value, it updates just fine, but after that the arrow buttons no longer function to further alter the age value in the <code>hintText</code>. </p>
  </blockquote>
  
  <p>However, the value is still being updated behind the scenes and can be viewed with a <code>print</code> function.</p>
  
  <p>Here's a simplified version of the code used:</p>
  
  <pre><code>TextField(
      onChanged: (val) {
            setState(() {
              age = int.parse(val);
            });,
      keyboardType: TextInputType.number,
      decoration: InputDecoration(
      border: InputBorder.none,
      hintText: age.toString(),
      hintStyle: TextStyle(
          color: Color(0xFF999999), fontWeight: FontWeight.bold),
    ),
  )
  
  
  Container(
        child: RawMaterialButton(
          onPressed: chngAge,
  )
  
  
  void chngAge() {
      setState(() {
        age++;
      });
    }
  </code></pre>
  
  <p>I'm wondering if after some text has been input into a text field that it is not longer <code>hintText</code> and thus cannot be updated in this way?</p>