Question

我是新手，只是想了解简单的概念。我已经阅读了目标C for dummies和Cocoa Programming for Mac OSX（大部分内容）。我试着自己制作一个简单的小程序，并意识到我知之甚少。

我一直收到"Use of Undeclared Identifier "calculateAge', did you mean 'Calculate' "错误。

任何人都可以告诉我下面的代码有什么问题，为什么？先谢谢了。

#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

您似乎将方法名称与参数列表混为一谈。正确的签名看起来像这样：

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

然后可以这样实现：

- (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;
}

然后可以这样调用：

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

不要在类实现中实现main;它属于全局命名空间外部，最好是在自己的文件中。

Answer 2

无需在界面中声明实例变量最后@end需要在main函数之前，它不是类的一部分，它使用了类需要实例化Calculate类，并且需要对实例化的类进行调用应重命名calculateAge...方法以指示每个参数变量应该被赋予全名，通常的缩写最终会使事情变得不那么明确。

以下是一个例子：

@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;
}

NSLog输出：

你好，世界！
诞生年份是：1963年年龄是：49
现在年份是：2012年年龄是：49

使用`@ property~ statements：

创建的实例变量

@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;
}

使用未声明的标识符＆＃39; calculateAge＆＃39;

2 个答案: