Flutter 单例的实现

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前言

回顾iOS，单例的写法如下：

static JXWaitingView *shared;

+(JXWaitingView*)sharedInstance{
  static dispatch_once_t onceToken;
  dispatch_once(&onceToken, ^{
      shared=[[JXWaitingView alloc]initWithTitle:nil];
  });
  return shared;
}

其目的是通过dispatch_once来控制【初始化方法】只会执行一次，然后用static修饰的对象来接收并返回它。所以核心是只会执行一次初始化。

创建单例

创建单例的案例

class Student {
  String? name;
  int? age;
  //构造方法
  Student({this.name, this.age});

  // 单例方法
  static Student? _dioInstance;
  static Student instanceSingleStudent() {
    if (_dioInstance == null) {
      _dioInstance = Student();
    }
    return _dioInstance!;
  }
}

测试单例效果

测试一

import 'package:flutter_async_programming/Student.dart';

void main() {
  Student studentA = Student.instanceSingleStudent();
  studentA.name = "张三";
  Student studentB = Student.instanceSingleStudent();
  print('studentA姓名是${studentA.name}');
  print('studentB姓名是${studentB.name}');
}

运行效果

测试二

import 'package:flutter_async_programming/Student.dart';

void main() {
  Student studentA = Student.instanceSingleStudent();
  studentA.name = "张三";
  Student studentB = Student.instanceSingleStudent();
  studentB.name = "李四";
  print('studentA姓名是${studentA.name}');
  print('studentB姓名是${studentB.name}');
}

运行效果