cllocation子类化错误

我正在尝试创建一个新的cllocation子类。这是骨架:

#import <UIKit/UIKit.h>
#import <CoreLocation/CoreLocation.h>

@interface JFLocation : CLLocation {

}

@end


#import "JFLocation.h"


@implementation JFLocation

@end

当我构建类时,会收到以下错误:

Undefined symbols:
  ".objc_class_name_CLLocation", referenced from:
      .objc_class_name_JFLocation in JFLocation.o
ld: symbol(s) not found

有什么想法吗?谢谢!!