• StatelessWidget : 不可变，比例一旦定义了宽高，一旦定义就不可改变
• StatefulWidget :==需要两个类去管理==
• 描述UI
• 记录状态的State (w,h)不销毁,界面消失才会被干掉 : State属性改变时会根据宽高重新渲染UI

1.StatelessWidget(界面本身不发生变化)

UI 界面一旦创建就不会发生变化,定义属性值可以变化,但不会重新渲染UI,

所有的界面都是不可变的(无状态的)

//Chip 悬浮小图标
class StateManagerDemo extends StatelessWidget {
  int count = 0;//提示你去用final 修饰
  void func(){
    count += 1;
    print('count = $count');
    /*
    输出结果
    flutter: count = 1
    flutter: count = 2
    flutter: count = 3
    flutter: count = 4
    flutter: count = 5
    */
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("StateManagerDemo"),
      ),
      body: Center(
        child: Chip(label: Text('$count')),
      ),
      floatingActionButton: FloatingActionButton(
        child: Icon(Icons.add),
        onPressed: func,
      ),
    );
  }
}

2.StatefulWidget(界面本身发生变化)

• State发生变化时会重新渲染UI，类似于Hot Reload
• 更新/刷新操作：setState(() {});
• createState 此方法返回状态管理类，进行关联

所有的界面都是不可变的(无状态的)

//RXDart
//1.定义UI类
class StateManagerDemo extends StatefulWidget {
  //构造方法-初始化数据，传参数
  @override
  State<StatefulWidget> createState() {
    // TODO: implement createState
    return _SMDState();
  }
}
//2.定义状态管理类
class _SMDState extends State<StateManagerDemo> {
  //状态->>管理数据
  int count = 0;
  void func(){
    count += 1;
    setState(() {});//重新刷新
    print('count = $count');
  }
  @override
  Widget build(BuildContext context) {
    // TODO: implement build
    return Scaffold(
      appBar: AppBar(
        title: Text("StateManagerDemo"),
      ),
      body: Center(
        child: Chip(label: Text('$count')),
      ),
      floatingActionButton: FloatingActionButton(
        child: Icon(Icons.add),
        onPressed: func,
      ),
    );
  }
}

效果图

image