Question

我似乎无法解决这个错误;使用未声明的标识符'ageBy'。我不明白为什么我得到它，因为我在我的代码中有导入Person.h。感谢您的时间和任何帮助。

Person.h

@interface Person : NSObject
{
 int _age;
 int _years;
 NSString *_name;
 NSString *_job;

} 

-(void)setAge:(int)age;
-(int)age;

-(void)setName:(NSString *)name;
-(NSString *)name;

-(void)setJob:(NSString *)job;
-(NSString *)job;

-(NSString *)summaryString;

-(void)ageBy:(int)years;


@end

Person.m

#import "Person.h"
@implementation Person

-(void)setAge:(int)age{
  _age = age;
}
-(int)age{
  return _age;
}
-(void)setName:(NSString *)name{
  _name = name;
}
-(NSString *)name{
  return _name; }

-(void)setJob:(NSString *)job{
  _job = job;
}
-(NSString *)job{
  return _job;
}

-(NSString *)summaryString{
  return [NSString stringWithFormat:@"The Person %@ is %d years old and is a  %@",_name,_age,_job];

-(void)ageBy:(int)years{
  _years = years;
  _age = years + _age;

 }

 } 
 @end

Answer 1

您的ageBy:在summaryString内定义。您可能希望在@end之前移动大括号，使其高于-(void)ageBy:(int)years。所以：

-(NSString *)summaryString{
  return [NSString stringWithFormat:@"The Person %@ is %d years old and is a  %@",_name,_age,_job];
 } 

-(void)ageBy:(int)years{
  _years = years;
  _age = years + _age;

 }

同样作为样式注释，如果summaryString仅用于调试，那么您可能最好将其声明为description。后者是获取Objective-C对象的实现依赖和字符串描述的标准形式，具有像NSArray这样的集合对象知道在其所有子对象上调用description的净效果，以便创建正确的输出。

Answer 2

如上所述，问题是由ageBy:方法中嵌入summaryString方法引起的。

我想演示如何使用现代Objective-C编写这个类：

// Person.h
@interface Person : NSObject

@property (nonatomic, assign) int age;
@property (nonatomic, copy) NSString *name;
@property (nonatomic, copy) NSString *job;

- (void)ageBy:(int)years;

@end

// Person.m
@implementation Person

- (NSString *)description {
    return [NSString stringWithFormat:@"The Person %@ is %d years old and is a %@", self.name, self.age, self.job];
}

- (void)ageBy:(int)years {
    self.age = self.age + years;
}

@end

未声明的标识符目标C.

2 个答案: