ios - 无法以编程方式在 View Controller 之间切换

Question

下面显示的是我用来在代码中的两个 View Controller 之间传输的代码。这不起作用并会导致错误 THREAD 1 Signal SIGBART。

 func nextPage() {
    //we are on the last page
    if pageControl.currentPage == pages.count {
        /*moveControlConstraintsOffScreen()

        UIView.animate(withDuration: 0.5, delay: 0, usingSpringWithDamping: 1, initialSpringVelocity: 1, options: .curveEaseOut, animations: {
            self.view.layoutIfNeeded()
        }, completion: nil)
        */
        let vc = self.storyboard?.instantiateViewController(withIdentifier: "logloginControllerID") as! logloginController
        self.present(vc, animated: true, completion:nil)
    }

    //second last page
    if pageControl.currentPage == pages.count {
       return
    }

    let indexPath = IndexPath(item: pageControl.currentPage + 1, section: 0)
    collectionView.scrollToItem(at: indexPath, at: .centeredHorizontally, animated: true)
    pageControl.currentPage += 1
}

这是崩溃时的完整控制台输出:

2017-06-27 13:57:13.823 College Search[80667:48415876] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'attempt to scroll to invalid index path:  {length = 2, path = 0 - 3}'
*** First throw call stack:
(
    0   CoreFoundation                      0x0000000104121b0b __exceptionPreprocess + 171
    1   libobjc.A.dylib                     0x0000000103771141 objc_exception_throw + 48
    2   CoreFoundation                      0x000000010418a625 +[NSException raise:format:] + 197
    3   UIKit                               0x0000000105a0881f -[UICollectionView _contentOffsetForScrollingToItemAtIndexPath:atScrollPosition:] + 216
    4   UIKit                               0x0000000105a09250 -[UICollectionView scrollToItemAtIndexPath:atScrollPosition:animated:] + 70
    5   College Search                      0x0000000102d4387f _TFC14College_Search15LogInController8nextPagefT_T_ + 1343
    6   College Search                      0x0000000102d43a32 _TToFC14College_Search15LogInController8nextPagefT_T_ + 34
    7   UIKit                               0x00000001050c6d22 -[UIApplication sendAction:to:from:forEvent:] + 83
    8   UIKit                               0x000000010524b25c -[UIControl sendAction:to:forEvent:] + 67
    9   UIKit                               0x000000010524b577 -[UIControl _sendActionsForEvents:withEvent:] + 450
    10  UIKit                               0x000000010524a4b2 -[UIControl touchesEnded:withEvent:] + 618
    11  UIKit                               0x000000010513449a -[UIWindow _sendTouchesForEvent:] + 2707
    12  UIKit                               0x0000000105135bb0 -[UIWindow sendEvent:] + 4114
    13  UIKit                               0x00000001050e27b0 -[UIApplication sendEvent:] + 352
    14  UIKit                               0x000000011543175c -[UIApplicationAccessibility sendEvent:] + 85
    15  UIKit                               0x00000001058c5adc __dispatchPreprocessedEventFromEventQueue + 2926
    16  UIKit                               0x00000001058bda3a __handleEventQueue + 1122
    17  CoreFoundation                      0x00000001040c7c01 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 17
    18  CoreFoundation                      0x00000001040ad0cf __CFRunLoopDoSources0 + 527
    19  CoreFoundation                      0x00000001040ac5ff __CFRunLoopRun + 911
    20  CoreFoundation                      0x00000001040ac016 CFRunLoopRunSpecific + 406
    21  GraphicsServices                    0x0000000109a94a24 GSEventRunModal + 62
    22  UIKit                               0x00000001050c50d4 UIApplicationMain + 159
    23  College Search                      0x0000000102d4ac67 main + 55
    24  libdyld.dylib                       0x00000001070b165d start + 1
)
libc++abi.dylib: terminating with uncaught exception of type NSException
(lldb) 

Answer 1

哦，好吧，我看到了编辑。假设您现在有 3 个页面。在页面数组中，您的页面编号为 0、1、2。

现在假设您位于倒数第二页。这让你的分数为 1，对吗？让我们转到下一页，即 2。现在，您的逻辑(在您的头脑中)是说如果当前页面 = pages.count 则执行某些操作。这个逻辑用基本术语来说就是“一旦到达最后页面就加载此 View Controller ”。

你实际上在做的是别的事情。 page.count = 3 因为该数组中有 3 项。因此，您的 currentPage 必须等于 3 才能使该逻辑起作用。因此，当您的 currentPage = 2 (实际上是真正的最后一页)时，您会跳过 currentPage == pages.count 的条件，最终会尝试加载 3 的索引路径。那不存在

所以你需要做的就是改变你的状况。您需要这样做，而不是 currentPage == pages.count :

当前页 == 页数.count - 1

之后你应该会没事的。