I' m gettings items from JSON and displaying them in a dropdown. When the person select an item from the dropdown list, I get the selection but the selected item doesn't change.

For example we have (tokyo, paris, new york) in the list. By default selection is tokyo. When the person select paris, I get it but the selection doesn't change in the dropdown.

Here is my code:

```
new DropdownButton(
  value: cities.elementAt(0),
  hint: new Text("Ville"),
  items: cities.map((String value) {
    return new DropdownMenuItem(
      value: value,
      child: new Row(
        children: <Widget>[
          new Icon(
            Icons.location_city,
            color: Colors.deepOrange,
          ),
          new Text(value)
        ],
      ),
    );
  }).toList(),
  onChanged: (String value) {
    getTravelCity(value);
  },
),

```

When the person select an item, it still showing the default value.