indexofobject返回零

Question

我正在尝试使用从故事板构建的场景来构建应用程序的演练.

所以我填充了我的viewControllers数组,称为pages:

@interface PVCPagesViewController () {
    NSMutableArray *pages;
}

@property (retain, nonatomic) NSMutableArray *pages;
@property (strong, nonatomic) UIPageViewController *pageController;


@end

在viewDidLoad()中:

self.pages = [[NSMutableArray alloc] init];

UIViewController *page1 = [[UIStoryboard storyboardWithName:@"Main" bundle:nil] instantiateViewControllerWithIdentifier:@"page1"];

UIViewController *page2 = [[UIStoryboard storyboardWithName:@"Main" bundle:nil] instantiateViewControllerWithIdentifier:@"page2"];

UIViewController *page3 = [[UIStoryboard storyboardWithName:@"Main" bundle:nil] instantiateViewControllerWithIdentifier:@"page3"];

UIViewController *page4 = [[UIStoryboard storyboardWithName:@"Main" bundle:nil] instantiateViewControllerWithIdentifier:@"page4"];

self.pages = [[NSMutableArray alloc] initWithObjects:page1, page2, page3, page4, nil];

但是当我要在viewControllerAfterViewController()中从数组加载另一个视图控制器时:

- (UIViewController *)pageViewController:(UIPageViewController *)pageViewController viewControllerAfterViewController:(UIViewController *)viewController {

    NSInteger index = [self.pages indexOfObject:viewController];

    index++;

    return [self.pages objectAtIndex:index];
}

我得到一个有效的viewController,我在数组中看到它,但是当我尝试objectAtIndex时,它返回nil？

(lldb) po self.pages
<__NSArrayM 0x170243cc0>(
<UIViewController: 0x13cd05370>,
<UIViewController: 0x13cd06030>,
<UIViewController: 0x13ce00000>,
<UIViewController: 0x13ce11b60>
)

(lldb) po viewController
<UIViewController: 0x13cd05370>
(lldb) po [self.pages indexOfObject:viewController];
<nil>
(lldb) 

是什么赋予了？提前致谢

Answer 1

indexOfObject:不返回一个对象,这是pocommand(print --object-description)所期望的; 它返回一个NSUInteger.使用plain print命令:

(lldb) p (NSUInteger)[self.pages indexOfObject:viewController];
0

使用时po,索引0被解释为对象指针.0指针是nil,所以这是打印的.如果它是任何其他值,调试器将不知道如何处理它,因为它几乎肯定不会是一个有效的对象指针.