implemented: dropdown_button example

dropdown_button/lib/main.dart

@@ -2,7 +2,40 @@ import 'package:flutter/material.dart';
 
 void main() => runApp(new MyApp());
 
-class MyApp extends StatelessWidget {
+class MyApp extends StatefulWidget {
+  @override
+  State<StatefulWidget> createState() {
+    return new MyAppState();
+  }
+}
+
+class MyAppState extends State<MyApp> {
+  List _fruits = ["Apple", "Banana", "Pineapple", "Mango", "Grapes"];
+
+  List<DropdownMenuItem<String>> _dropDownMenuItems;
+  String _selectedFruit;
+
+  @override
+  void initState() {
+    _dropDownMenuItems = buildAndGetDropDownMenuItems(_fruits);
+    _selectedFruit = _dropDownMenuItems[0].value;
+    super.initState();
+  }
+
+  List<DropdownMenuItem<String>> buildAndGetDropDownMenuItems(List fruits) {
+    List<DropdownMenuItem<String>> items = new List();
+    for (String fruit in fruits) {
+      items.add(new DropdownMenuItem(value: fruit, child: new Text(fruit)));
+    }
+    return items;
+  }
+
+  void changedDropDownItem(String selectedFruit) {
+    setState(() {
+      _selectedFruit = selectedFruit;
+    });
+  }
+
   @override
   Widget build(BuildContext context) {
     return new MaterialApp(
@@ -11,7 +44,19 @@ class MyApp extends StatelessWidget {
           title: new Text("DropDown Button Example"),
         ),
         body: new Container(
-          child: new Center(child: new Text("Hello World")),
+          child: new Center(
+              child: new Column(
+            crossAxisAlignment: CrossAxisAlignment.center,
+            mainAxisAlignment: MainAxisAlignment.center,
+            children: <Widget>[
+              new Text("Please choose a fruit: "),
+              new DropdownButton(
+                value: _selectedFruit,
+                items: _dropDownMenuItems,
+                onChanged: changedDropDownItem,
+              )
+            ],
+          )),
         ),
       ),
     );