代码如下：
apple.h

1. #import <Foundation/Foundation.h>
   
2. 
   
3. @interface Apple : NSObject
   
4. 
   
5. @property int num;
   
6. @property int size;
   
7. 
   
8. - (void)test;
   
9. - (int)appleSize;
   
10. 
    
11. @end

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apple.m

1. #import "Apple.h"
   
2. 
   
3. @implementation Apple
   
4. 
   
5. - (void)test
   
6. {
   
7.     NSLog(@"apple");
   
8. }
   
9. 
   
10. - (int)appleSize
    
11. {
    
12.     return _size;
    
13. }
    
14. 
    
15. @end

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plum.h

1. #import <Foundation/Foundation.h>
   
2. 
   
3. @interface Plum : NSObject
   
4. 
   
5. @property int num;
   
6. @property int size;
   
7. 
   
8. - (void)test;
   
9. - (int)plumSize;
   
10. 
    
11. @end

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plum.m

1. #import "Plum.h"
   
2. 
   
3. @implementation Plum
   
4. 
   
5. - (void)test
   
6. {
   
7.     NSLog(@"plum");
   
8. }
   
9. 
   
10. - (int)plumSize
    
11. {
    
12.     return _size;
    
13. }
    
14. 
    
15. @end

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main.m

1. #import <Foundation/Foundation.h>
   
2. #import "Apple.h"
   
3. #import "Plum.h"
   
4. 
   
5. int main()
   
6. {
   
7.     Apple *a = [Apple new];
   
8.     a.num = 5;
   
9.     NSLog(@"num = %d",a.num);
   
10.    
    
11.     Plum *p = [Plum new];
    
12.     p.num = 8;
    
13.     NSLog(@"num = %d",p.num);
    
14.    
    
15.     id data=a;
    
16.     [data test];
    
17.     int size = [data appleSize];
    
18.     NSLog(@"size = %d",[data appleSize]);
    
19.    
    
20.     data = p;
    
21.     [data test];
    
22.     size = [data plumSize];
    
23.     NSLog(@"size = %d",size);
    
24.    
    
25.     return 0;
    
26. }

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代码运行时报错如下：

问一下这样得怎样修改，为什么id类型转化成了别的类型。为什么可以准确调用appleSize方法，就是不能调用test方法

没人啊，自己顶一个吧