Flutter 有两种基本的 widget 类型:StatelessWidget(不可变,没有会改变的内部状态)和 StatefulWidget(可以持有和更新可变状态,当状态改变时重新构建)。选择正确的类型是构建 Flutter UI 的基础。
StatelessWidget — 没有变化的状态
// a StatelessWidget: just describes UI based on its inputs (immutable, no internal state)
class Greeting extends StatelessWidget {
final String name;
const Greeting(this.name);
@override
Widget build(BuildContext context) {
return Text('Hello, $name'); // UI depends only on inputs, never changes itself
}
}
// → use for UI that doesn't change on its own (static content, displays based on inputs)
