Add pick random letter feature

lib/main.dart

 import 'package:flutter/material.dart';
+import 'dart:math';
 
 void main() {
   runApp(MyApp());
@@ -21,12 +22,21 @@ class MyHomePage extends StatefulWidget {
   MyHomePage({Key key, this.title}) : super(key: key);
 
   final String title;
+  final Random _rnd = Random();
+  final String _chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ';
 
   @override
   _MyHomePageState createState() => _MyHomePageState();
 }
 
 class _MyHomePageState extends State<MyHomePage> {
+  String _randomLetter = '';
+
+  void _pickRandomLetter() {
+    setState(() {
+      _randomLetter = widget._chars[widget._rnd.nextInt(widget._chars.length)];
+    });
+  }
 
   @override
   Widget build(BuildContext context) {
@@ -39,11 +49,19 @@ class _MyHomePageState extends State<MyHomePage> {
           mainAxisAlignment: MainAxisAlignment.center,
           children: <Widget>[
             Text(
-              'X',
+              'Lettre aléatoire :',
+            ),
+            Text(
+              '$_randomLetter',
+              style: Theme.of(context).textTheme.headline4,
             ),
           ],
         ),
       ),
+      floatingActionButton: FloatingActionButton(
+        onPressed: _pickRandomLetter,
+        child: Icon(Icons.shuffle),
+      ),
     );
   }
 }