ios-IOS- “This class is not key value coding-compliant”

IOS- “This class is not key value coding-compliant”

在ios應用中聲明：

@interface UserRegistrationRequest : BaseServiceRequest
@property (nonatomic, retain) NSString *username;
@property (nonatomic, retain) NSString *password;
@property (nonatomic, retain) NSString *secretQuestionID;
@property (nonatomic, retain) NSString *secretQuestionAnswer;
@property (nonatomic, retain) UserProfile *profile;

@end

@interface UserProfile : NSObject
@property (nonatomic, retain) NSString *emailAddress;
@property (nonatomic, retain) NSString *firstName;
@property (nonatomic, retain) NSString *lastName;
@property (nonatomic, retain) NSData *profileImage;
@property (nonatomic, retain) NSNumber *dateOfBirth;
@end

我認為這些類應該是鍵值編碼兼容
運行下面的代碼：

NSString *propKey = @"profile.firstName";
NSString *propVal = [self.registrationRequest valueForKey:propKey];

報出異常：

[<UserRegistrationRequest 0xb6187f0> valueForUndefinedKey:]: this class is not key value coding-compliant for the key profile.firstName.

不知道應該怎麼解決？

最佳回答：

使用這個：

NSString *propVal = [self.registrationRequest valueForKeyPath:propKey];