Question

我已经定义了NSMutableArray的属性。在致电initWithObjects后，它count为0.我在这里缺少什么？这是我的代码：

@interface MainViewController ()
@property NSMutableArray *photos;
@end

- (void)viewDidLoad {
    [super viewDidLoad];

    _photos = [_photos initWithObjects:@"1", @"2", @"3", nil];
    NSLog(@"Photos count: %lu",(unsigned long)_photos.count); //prints 0
}

Answer 1

这是因为您尝试调用_photos方法时nil为init。请改用arrayWithObjects：

_photos = [NSMutableArray arrayWithObjects:@"1", @"2", @"3", nil];

Answer 2

非法在init...中说alloc并且在同一行中说alloc。 _photos = [[NSMutableArray alloc] initWithObjects:@"1", @"2", @"3", nil];是一个类方法，你的类是NSMutableArray，所以你应该说：

public class control_it extends HttpServlet{
private static final long serialVersionUID = 1L;

public control_it () {
    super();
}

    protected void doGet(HttpServletRequest request, 
            HttpServletResponse response) 
                  throws IOException, ServletException {

        String name = "Display the name";
        request.setAttribute("name",name);

         RequestDispatcher rd=request.getRequestDispatcher("try_it.jsp");   
         rd.forward(request,response);      
   }
}

initWithObject之后NSMutableArray计数为0

2 个答案: