最近項(xiàng)目中遇到一個(gè)問題，寫了一個(gè)繼承于NSObject的類用于處理服務(wù)器返回的數(shù)據(jù)，其中當(dāng)服務(wù)器返回某個(gè)數(shù)值時(shí)會(huì)執(zhí)行跳轉(zhuǎn)到登錄頁面的操作，比如登陸過期，但是發(fā)現(xiàn)實(shí)際上是無法觸發(fā)VC跳轉(zhuǎn)的，報(bào)出警告如下：
Warning: Attempt to present <UINavigationController: 0x7f818a07f200> on <UINavigationController: 0x7f818a024400> whose view is not in the window hierarchy!
代碼如下：

EALoginViewController *loginVC = [EALoginViewController new];
            UINavigationController *navc = [[UINavigationController alloc] initWithRootViewController:loginVC];
            [topRootViewController presentViewController:navc animated:YES completion:nil];

查閱資料才了解到應(yīng)該是VC的生命周期執(zhí)行順序?qū)е麓a無法觸發(fā)，最后找到解決辦法，代碼如下：

UIViewController *topRootViewController = [UIApplication sharedApplication].keyWindow.rootViewController;
            while (topRootViewController.presentedViewController)
            {
                topRootViewController = topRootViewController.presentedViewController;
            }
            
            EALoginViewController *loginVC = [EALoginViewController new];
            UINavigationController *navc = [[UINavigationController alloc] initWithRootViewController:loginVC];
            [topRootViewController presentViewController:navc animated:YES completion:nil];