报错：
*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[NSURLError isEqualToString:]: unrecognized selector sent to instance 0x10b34e810'
*** First throw call stack:
*** First throw call stack:
(lldb) po 0x10b34e810
Error Domain=NSURLErrorDomain Code=-1004 "Could not connect to the server." UserInfo=0x10a582670 {NSUnderlyingError=0x10a664e90 "Could not connect to the server.", NSErrorFailingURLStringKey= , NSLocalizedDescription=Could not connect to the server.}
Error Domain=NSURLErrorDomain Code=-1004 "Could not connect to the server." UserInfo=0x10a582670 {NSUnderlyingError=0x10a664e90 "Could not connect to the server.", NSErrorFailingURLStringKey= , NSLocalizedDescription=Could not connect to the server.}
打印了 0x10b34e810对象，怀疑 NSError *error 强制转成string类型的不成功
在这里挂掉了。。。
(lldb) po (NSString*)error
Error Domain=NSURLErrorDomain Code=-1004 "Could not connect to the server." UserInfo=0x10a5223a0 {NSUnderlyingError=0x10b181140 "Could not connect to the server.", NSErrorFailingURLStringKey=, NSLocalizedDescription=Could not connect to the server.}
Error Domain=NSURLErrorDomain Code=-1004 "Could not connect to the server." UserInfo=0x10a5223a0 {NSUnderlyingError=0x10b181140 "Could not connect to the server.", NSErrorFailingURLStringKey=, NSLocalizedDescription=Could not connect to the server.}
总结：数值基本类型的可以转，nsobject类型的不能够强制转（一般普通的基本类型可以强制转化。int，float可以转成string 。对象类型的是不是不可以转化啊。。比如nsurl的不可以转成string。。nserror也不可以转成string）多么基本的常识丫，还总是忘了。
