单例设计模式

static UserContext *segtonInstance = nil;

@implementation UserContext

+(id)shareUserContext{
    @synchronized(self){
        //线程安全
        if (segtonInstance == nil) {

            segtonInstance = [[[self class] alloc] init];
        }
    }
    return segtonInstance;
}

//重写 allocWithZone: 方法
+(id)allocWithZone:(NSZone *)zone{
    if (segtonInstance == nil) {
        segtonInstance = [super allocWithZone:zone];
    }
    return segtonInstance;
}

- (id)copyWithZone:(NSZone *)zone
{
    return segtonInstance;
}

//覆盖 release，autorelease，retain，retainCount 方法方法

//返回本身
-(id)retain
{
    return self;
}

-(NSInteger)retainCount
{
    return UINT_MAX;
}

-(id)autorelease{
    return self;
}
-(oneway void)release
{

}

//验证单例
  UserContext *user1 = [UserContext shareUserContext];
        UserContext *user2 = [UserContext shareUserContext];
        UserContext *user3 = [[UserContext alloc] init];
        UserContext *user4 = [[UserContext alloc] init];
        UserContext *user5 = [[UserContext copy];

        NSLog(@"%@",user1);
        NSLog(@"%@",user2);
        NSLog(@"%@",user3);
        NSLog(@"%@",user4);
        NSLog(@"%@",user5);