未将对象添加到 NSMutableArray [重复]

Question

Student.h

#import <Foundation/Foundation.h>

@interface Student : NSObject
@property NSInteger age;
@property NSString *name;
@end

Student.m

#import "Student.h"
@implementation Student
@end

StudentCount.h

#import <Foundation/Foundation.h>
#import "Student.h"
NSMutable
@interface StudentCount : NSObject
@property NSMutableArray<Student *> *student;
-(void)addStu:(Student *)stud;
-(void)printStudents;
@end

StudentCount.m

#import "StudentCount.h"

@implementation StudentCount
-(void)addStu:(Student *)stud{
    [_student addObject:stud];
}
-(void)printStudents{
    for(Student *s in _student){
        NSLog(@"%li",s.age);
        NSLog(@"%@",s.name);
    }
}
@end

Main.m

#import <Foundation/Foundation.h>
#import "Student.h"
#import "StudentCount.h"

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        Student *student1=[Student alloc];
        student1.age=10;
        student1.name=@"Nirmal";

        Student *student2=[Student alloc];
        student2.age=12;
        student2.name=@"Anand";

        StudentCount *stCount=[StudentCount alloc];
        [stCount addStu:student1];
          [stCount addStu:student2];

        [stCount printStudents];


    }
    return 0;
}

在上面的程序中，我尝试将学生对象添加到 StudentCount 类的NSMutableArray。 之后，我尝试调用 StudentCount 类的 printStudents 方法。 学生对象不会添加到NSMutableArray。

上述程序的输出：

程序以退出代码结束：0

请告知我哪里出错了。

Answer 1

您需要分配NSMutableArray * student。

-(void)addStudent:(Student *)stud
{
    if (_student == nil) {
        _student = [[NSMutableArray alloc] init];
    }
    [_student addObject:stud];
}