Dart语言单例模式的各种写法

骑猪看日落 2023-10-09 13:35 8阅读 0赞

#### 方式一 ####

class Singleton {
        
      factory Singleton() =>
          const Singleton._internal_();
      const Singleton._internal_();
    }

这种方式和普通new没有区别，但是实例确是同一个

void main(){
        
        var result = new Singleton();
        var result2 = Singleton();
        print(result == result2);
    }

#### 方法二 ####

class Singleton {
        
      Singleton._privateConstructor();
    
      static final Singleton _instance = Singleton._privateConstructor();
    
      factory Singleton(){
        
        return _instance;
      }
    }

这种方式不需要调用`.instance`，但是实例确是同一个

var instance1 = Singleton();
        var instance2 = Singleton();
        print(result == result2);

#### 方式三 ####

class Singleton {
        
      Singleton._internal();
    
      static final Singleton _instance = Singleton._internal();
    
      static Singleton getInstance() {
        
        return _instance;
      }
    }

使用

void main() {
        
    	var instance = Singleton.getInstance();
    	var instance2 = Singleton.getInstance();
        print(result == result2);
    }

#### 方式四 ####

class Singleton {
        
    	// 私有化构造方法
    	Singleton._privateConstructor();
    	
    	static final Singleton _instance = Singleton._privateConstructor();
    	
    	//同下 : static Singleton get instance => _instance;
    	static Singleton get instance {
         return _instance;}
    }

使用

void main() {
        
    	var instance = Singleton.instance;
        var instance2 = Singleton.instance;
        print(instance == instance2);
    }

#### 方式五 ####

class Singleton {
        
    	Singleton._privateConstructor();
    	static final Singleton instance = Singleton._privateConstructor();
    }

使用

void mian(){
        
    	var instance = Singleton.instance;
        var instance2 = Singleton.instance;
        print(instance == instance2);
    }

##### 其他 #####

> 参考 [https://www.wodecun.com/blog/8088.html][https_www.wodecun.com_blog_8088.html]

[https_www.wodecun.com_blog_8088.html]: https://www.wodecun.com/blog/8088.html