使用未聲明的標識符'calculateAge'

Question

我是新來的客觀，只是試圖理解簡單的概念。 我已經閱讀Objective C for傻瓜和Mac OSX的可可編程（大部分）。 我試圖自己製作一個簡單的小程序，並意識到我知道的很少。我不斷收到"Use of Undeclared Identifier "calculateAge', did you mean 'Calculate' "錯誤。

任何人都可以告訴我下面的代碼有什麼問題，爲什麼？ 預先感謝一堆。

#import <Foundation/Foundation.h> 


@interface Calculate : NSObject 
{ 
    int myYear; 
    int nowYear; 
} 


- (int) calculateAge:(int)birthYear:(int)nowYear; 

@end 



@implementation Calculate 



- (int) calculateAge:(int)birthYear:(int)nowYear// need myYear 
{ 

    NSLog(@"The birthYear is: %i\n", birthYear); 
    int myAge = nowYear - birthYear;   
    //NSLog(@"The nowYear is: %i\n", nowYear); 
    NSLog(@"The age is: %i\n", myAge); 
    return myAge; 
} 



int main(int argc, const char * argv[]) 
{ 

    @autoreleasepool { 


     NSLog(@"Hello, World!"); 
     int myY = 1963; 
     int nowY = 2012; 
     int myYear = 1963; 
     int nowYear = 2012; 
     //int myAge = calculateAge:(int) birthYear: (int) nowYear; 
     int myAge = calculateAge:(int) myY: (int) nowY; 
     NSLog(@"The nowYear is: %i\n", nowYear); 
     NSLog(@"The age is: %i\n", myAge); 

    } 
    return 0; 
} 
@end 

Answer 1

您似乎在將方法名稱與參數列表混合在一起。一個適當的簽名會是這個樣子：

- (int)calculateAgeFromBirthYear:(int)birthYear currentYear:(int)currentYear 

這可能再像這樣實現：

- (int)calculateAgeFromBirthYear:(int)birthYear currentYear:(int)currentYear 
{ 

    NSLog(@"The birthYear is: %i\n", birthYear); 
    int myAge = currentYear - birthYear;   
    //NSLog(@"The nowYear is: %i\n", currentYear); 
    NSLog(@"The age is: %i\n", myAge); 
    return myAge; 
} 

這可能然後這樣調用：

Calculate *calculator = [[Calculate alloc] init]; 
int myAge = [calculator calculateAgeFromBirthYear:myY currentYear:nowY]; 

不執行main裏面的一個類的實現;它屬於全局命名空間的外部，最好在其自己的文件中。

Answer 2

沒有必要在接口中聲明實例變量。
最後@end需要在主函數之前，它不是類的一部分，它使用了類。
需要對Calculate類進行實例化，並且需要對實例化的類進行調用。
calculateAge...方法應重命名以指示每個參數。
變量應該給全名，abreviations通常最終使事情不太清楚。

下面是一個例子：

@interface Calculate : NSObject 
- (int) calculateAgeWithBirthYear:(int)birthYear nowYear:(int)nowYear; 
@end 

@implementation Calculate 
- (int) calculateAgeWithBirthYear:(int)birthYear nowYear:(int)nowYear// need myYear 
{ 
    NSLog(@"The birthYear is: %i\n", birthYear); 
    int myAge = nowYear - birthYear; 
    NSLog(@"The age is: %i\n", myAge); 
    return myAge; 
} 
@end 

int main(int argc, const char * argv[]) 
{ 
    @autoreleasepool { 

     NSLog(@"Hello, World!"); 

     int myBirthYear = 1963; 
     int nowYear = 2012; 

     Calculate *calculator = [[Calculate alloc] init]; 
     int myAge = [calculator calculateAgeWithBirthYear:myBirthYear nowYear:nowYear]; 

     NSLog(@"The nowYear is: %i\n", nowYear); 
     NSLog(@"The age is: %i\n", myAge); 

    } 
    return 0; 
} 

的NSLog輸出：

你好，世界！
的birthYear是：1963年
的年齡：49
的nowYear是：2012
的年齡：49

使用`@財產〜語句創建實例變量：

@interface Calculate : NSObject 
@property int myYear; 
@property int nowYear; 

- (int) calculateAge; 
@end 

@implementation Calculate 
- (int) calculateAge // need myYear 
{ 
    NSLog(@"The birthYear is: %i\n", self.myYear); 
    int myAge = self.nowYear - self.myYear; 
    NSLog(@"The age is: %i\n", myAge); 
    return myAge; 
} 
@end 

int main(int argc, const char * argv[]) 
{ 
    @autoreleasepool { 

     NSLog(@"Hello, World!"); 

     Calculate *calculator = [[Calculate alloc] init]; 
     calculator.myYear = 1963; 
     calculator.nowYear = 2012; 

     int myAge = [calculator calculateAge]; 

     NSLog(@"The nowYear is: %i\n", calculator.nowYear); 
     NSLog(@"The age is: %i\n", myAge); 

    } 
    return 0; 
}