单例的两种创建方法

1.线程保护

static MyClass instance = nil;

+(MyClass *)shareInstance{

@synchornized(self){

if(instance == nil) {

instance = [[MyClass alloc] init];

}

}

return instance;

}

2. GDC创建

static MyClass instance = nil;

+(MyClass *)shareInstance {

static dispatch_one_t  onceToke;

dispatch_one(&onceToke, ^{

instance = [[MyClass alloc] init];

});

return instance;

}