错误： [NSNull length]: unrecognized selector sent to instance 0x110504af0‘
查看数据发现，读取registerDate时，registerDate 是null，如果直接读取就报上面的错误：
{"userId":"1","nickName":"test","description":"my test desc","registerDate":null,"userHead":"res/default.jpg","sex":0,"age":null,"qq":"2345","state":1,"province":"shang xi","city":"xi an","longitude":null,"latitude":null}}
解决办法：
NSString *registerDateStr = [[userDic objectForKey:@"registerDate"] class] == [NSNull class]?@"暂无资料":[userDic objectForKey:@"registerDate"];
[regDate setText:registerDateStr];
iOS 错误： [NSNull length]: unrecognized selector sent to instance 0x110504af0'
原文：http://www.cnblogs.com/yuyu-2012/p/4854411.html