一个错误：
*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[NSURLError isEqualToString:]: unrecognized selector sent to instance
0x10b34e810'
*** First throw call stack:
0x10b34e810'
*** 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：数值基本类型的能够转，nsobject类型的不能够强制转（一般普通的基本类型能够强制转化。
int，float能够转成string 。
对象类型的是不是不能够转化啊。。
比方nsurl的不能够转成string。。nserror也不能够转成string）多么主要的常识丫，还总是忘了。
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