ios - 当 View Controller 超过 5 个时，为什么设置选项卡栏 Controller 的 selectedViewController >= 4 会抛出错误？

Question

我有一个以编程方式导航的 UITabBarController。调用如下方法:

// UITabBarController subclass

- (void)tabForward
{
    NSUInteger selectedIndex = [self.viewControllers indexOfObject:self.selectedViewController];
    selectedIndex = selectedIndex + 1;
    if ( selectedIndex < [self.viewControllers count] )
        self.selectedViewController = [self.viewControllers objectAtIndex:selectedIndex];
}

最初似乎工作正常，但随后同一行 (self.selectedViewController = [self.viewControllers objectAtIndex:selectedIndex];) 抛出错误，[__NSArrayM insertObject:atIndex:] : object cannot be nil, when there are more than 5 view controllers and selectedIndex == 4. 但是，如果我只是从选项卡栏 Controller 中删除任何 View Controller 以使总数达到 5 个 View Controller 或下面，不会抛出任何错误。这让我抓狂。有谁知道我做错了什么吗？

Answer 1

// UITabBarController subclass

- (void)tabForward
{
    NSInteger selectedIndex = [self.viewControllers indexOfObject:self.selectedViewController];
    NSInteger nextIndex = selectedIndex + 1;
    if (nextIndex < self.viewControllers.count) {
        if (nextIndex > 3) { // use navigation controller when selectedIndex >= 4
            self.selectedViewController = self.moreNavigationController;
            [self.moreNavigationController pushViewController:self.viewControllers[nextIndex] animated:YES];
        } else {
            self.selectedViewController = self.viewControllers[nextIndex];
        }
    }
}