ios - [NSConcreteValue rangeOfString :]: unrecognized selector sent to instance

Question

我尝试从字符串中获取范围，例如:

NSString *str  = change[@"new"];
NSLog(@"%@",str);// it will be printed

NSRange range = [str rangeOfString:@"NSPoint"];//the exception uncaughted
NSLog(@"%lu",range.location);  

但后来我遇到了一个异常(exception):

Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[NSConcreteValue rangeOfString:]: unrecognized selector sent to instance 0x7fc258c4f8f0'

令我困惑的是，如果我将 str 更改为 @"NSPoint: {0, 0}"会有效果吗？!天哪，为什么？

Answer 1

尝试

NSString *str  = [NSString stringWithFormat:@"%@",change[@"new"]];

代替

NSString *str  = change[@"new"];