苏州Flutter Widget 树与热重载

Widget 思想

UI 由嵌套 Widget 树描述。StatelessWidget 静态；StatefulWidget 持状态，状态变调 setState 重建。热重载（R 键）保留状态秒级刷新，开发体验极佳。

计数器示例

经典计数器展示 StatefulWidget + setState。

class Counter extends StatefulWidget {
  @override
  _CounterState createState() => _CounterState();
}
class _CounterState extends State<Counter> {
  int n = 0;
  @override
  Widget build(BuildContext c) => ElevatedButton(
    onPressed: () => setState(() => n++),
    child: Text('$n'),
  );
}