字典
报错Terminating app due to uncaught exception 'NSUnknownKeyException', reason: '[<__NSDictionaryI 0x7fdac26ea660> setValue:forUndefinedKey:]: this class is not key value coding-compliant for the key isDefault.
=> 只有可变的字典才能改变其中的值
报错Terminating app due to uncaught exception 'NSUnknownKeyException', reason: '[<__NSDictionaryI 0x7fdac26ea660> setValue:forUndefinedKey:]: this class is not key value coding-compliant for the key isDefault.
=> 只有可变的字典才能改变其中的值