Main.m

/*
 创建单例类
 */

int main(int argc, const char * argv[])
{

//    NSBundle *bundle = [NSBundle mainBundle];
//    NSFileManager *fileManager = [NSFileManager defaultManager];
    
    SingletonClass *single1 = [SingletonClass defaultClass];
    SingletonClass *single2 = [SingletonClass defaultClass];
    NSLog(@"single1:%@",single1);
    NSLog(@"single2:%@",single2);
    
    [single1 copy];
    
    //使用alloc方法创建
    SingletonClass *single3 = [[SingletonClass alloc] init];
    NSLog(@"single3:%@",single3);
    
    return 0;
}

+ (SingletonClass *)defaultClass;

//定义静态单例对象
static SingletonClass *single = nil;

@implementation SingletonClass

+ (SingletonClass *)defaultClass {

    if (single == nil) {
        single = [[SingletonClass alloc] init];
    }
    
    return single;
}

//alloc调用的方法
//zone是用来分配和释放内存的
+ (id)allocWithZone:(struct _NSZone *)zone {

    if (single == nil) {
        single = [super allocWithZone:zone];
    }
    
    return single;
}

- (id)copy {

    return self;
}

- (id)retain {

    return self;
}

- (oneway void)release {
    //什么都不做
}

//返回最大值，不让用户查阅引用计数
- (NSUInteger)retainCount {

    return UINT_MAX;
    
}

- (id)autorelease {

    return self;
}

创建单例类