iOS 创建单例

创建 SingleModel 类，第一种是用Grand Central Dispatch创建比较常用

//GCD创建

+(instancetype)shareSingleModel
{
   
   
    static SingleModel *single =nil;
   
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
       
        single = [[SingleModelalloc]init];
       
    });
   
   
    return single;
   
   
}

 

 第二种是简单的加锁
//加锁加锁
+(instancetype)shareSingleTwo
{
    static SingleModel *single =nil;
   
    @synchronized(self)  {
       
        if(single == nil)  {
           
            single = [[SingleModelalloc]init];
           
        }
       
    }
   
    return single;

}