Objective

前面我们学习了方法的注意事项, 这次我们来自己练习一回~~~

需求: 比如, 我需要知道两个人的体重差值是多少, 用一个方法来实现, 看看下面的例子:

#import <Foundation/Foundation.h>

@interface Preson : NSObject
{
    @public
    double weight;
}
- (double)myWeight:(Preson *)p;
@end

@implementation Preson
- (double)myWeight:(Preson *)p
{
    return weight - p->weight;
}
@end

int main()
{
    Preson *zhangsan = [Preson new];
    zhangsan->weight = 60.5;
    
    Preson *lisi = [Preson new];
    lisi->weight = 50;

    double a = [zhangsan myWeight:lisi];
    
    NSLog(@"他们之间相差%.2f/kg.", a);
    
    return 0;
}

输出的结果是:

2015-01-15 13:46:39.589 a.out[10220:1073260] 他们之间相差10.50/kg.

这里解释一下方法里面的weight和p->weight, 其实weight就是zhangsan的weight, 而p->weight是lisi的weight, 之前我们也知道, 谁调用方法, 那么里面的成员就是谁, 而参数里的指针就是传入进去的, 在这里是zhangsan在调用, 而传入的是lisi的地址, 最后运算完再把值返回.

其实我们可以尝试把地址打印出来看看:

#import <Foundation/Foundation.h>

@interface Preson : NSObject
{
    @public
    double weight;
}
- (double)myWeight:(Preson *)p;
@end

@implementation Preson
- (double)myWeight:(Preson *)p
{
    NSLog(@"weight的地址:%p", &weight);
    NSLog(@"p->weight:%p", &p->weight);

    return weight - p->weight;
}
@end

int main()
{
    Preson *zhangsan = [Preson new];
    zhangsan->weight = 60.5;
    
    NSLog(@"zhangsan体重的地址:%p", &zhangsan->weight);
    
    Preson *lisi = [Preson new];
    lisi->weight = 50;
    NSLog(@"lisi体重的地址:%p", &lisi->weight);

    
    double a = [zhangsan myWeight:lisi];
    
    NSLog(@"他们之间相差%.2f/kg", a);
    
    return 0;
}

输出的结果:

2015-01-15 13:46:39.588 a.out[10220:1073260] zhangsan体重的地址:0x7ff0e840e068
2015-01-15 13:46:39.589 a.out[10220:1073260] lisi体重的地址:0x7ff0e8410c68
2015-01-15 13:46:39.589 a.out[10220:1073260] weight的地址:0x7ff0e840e068
2015-01-15 13:46:39.589 a.out[10220:1073260] p->weight:0x7ff0e8410c68
2015-01-15 13:46:39.589 a.out[10220:1073260] 他们之间相差10.50/kg

在这里, zhangsan的地址和weight的地址是一样的, 而p->weight的地址和lisi的地址是一样的.

好了, 这次我们就到这里, 大家也可以自己回去试试看, 下次我们继续~~