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