常量

相同点

类型声明可以省略

final String a = 'ducafecat';
final a = 'ducafecat';

const String a = 'ducafecat';
const a = 'ducafecat';

初始后不能再赋值

final a = 'ducafecat';
a = 'abc';

const a = 'ducafecat';
a = 'abc';

不能和 var 同时使用

final var a = 'ducafecat';
const var a = 'ducafecat';

不同点

需要确定的值

final dt = DateTime.now();

const dt = const DateTime.now();

不可变性可传递

final List ls = [11, 22, 33];
ls[1] = 44;

const List ls = [11, 22, 33];
ls[1] = 44;

内存中重复创建

final a1 = [11 , 22];
final a2 = [11 , 22];
print(identical(a1, a2));

const a1 = [11 , 22];
const a2 = [11 , 22];
print(identical(a1, a2));

identical 通过比较两个引用的是否是同一个对象判断是否相等

使用场景

final 成员变量初始

class PlaceholdWidget extends StatelessWidget {

  final String? assetImagePath;

  const PlaceholdWidget({
    Key? key,
    this.assetImagePath,
  }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    ...
  }
}

const 全局参数

  // 本地存储key
  static const storageFirstOpen = 'first_open';
  static const storageLanguageCode = 'language_code';
  static const storageThemeCode = 'theme_code';
  static const storageToken = 'token';
  static const storageProfile = 'profile';