title: Drop down button in flutter not switching values to the selected value
body: <p>I've recently started programming using dart and flutter and everything has been going smoothly for my app, although recently i wanted to add drop down menu to provide the user with multiple options to pick from. everything worked as planned however when i pick a value from the list it doesn't change the value in the box, it goes back to the hint or an empty box. any help would be appreciated!</p>
  
  <p>here is my code for the dropdownbutton:</p>
  
  <pre><code>Widget buildDropdownButton() {
  String newValue;
  
  return new Padding(
    padding: const EdgeInsets.all(24.0),
    child: new Column(
      mainAxisAlignment: MainAxisAlignment.start,
      children: &lt;Widget&gt;[
        new ListTile(
          title: const Text('Frosting'),
          trailing: new DropdownButton&lt;String&gt;(
              hint: Text('Choose'),
              onChanged: (String changedValue) {
                newValue=changedValue;
                setState(() {
                  newValue;
                  print(newValue);
                });
              },
              value: newValue,
              items: &lt;String&gt;['None', 'Chocolate', 'Vanilla', 'ButterCream']
                  .map((String value) {
                return new DropdownMenuItem&lt;String&gt;(
                  value: value,
                  child: new Text(value),
                );
              }).toList()),
        ),
      ],
    ),
  );
  }
  </code></pre>