ios - 如何摆脱有关 View 相互叠加的通知？

Question

我有一个按钮可以执行 Segue 到另一个 View ，因此没有代码或操作连接到按钮，它全部使用 Storyboard完成，但在 prepareForSegue.

我添加了一个检查，以防特定值为 NULL，该检查按预期工作，但我确实在运行时收到此警告

2017-04-16 14:50:03.653 NWMobileTill[34117:830763] Warning: Attempt to present <TenderListView: 0x7ff81870b280>  on <TransactionListView: 0x7ff818738530> which is already presenting <UIAlertController: 0x7ff81864fff0>

我一般不喜欢运行时警告或编译器警告，那么我需要做什么才能消除此警告，同时在单击按钮时仍保持检查到位？

这是 prepareForSegue 片段

if ([[segue identifier] isEqualToString:@"trListViewToTenderList"]) {
    if([NWTillHelper getCurrentOrderNumber] == nil) {
        //Step 1: Create a UIAlertController
        UIAlertController *userInfoCheck = [UIAlertController alertControllerWithTitle:@"Tender"
                                                                               message: @"No active transaction, you need to have an active transaction before you can add tenders!"
                                                                        preferredStyle:UIAlertControllerStyleAlert];

        //Step 2: Create a UIAlertAction that can be added to the alert
        UIAlertAction* ok = [UIAlertAction
                             actionWithTitle:@"OK"
                             style:UIAlertActionStyleDefault
                             handler:^(UIAlertAction * action)
                             {
                                 [userInfoCheck dismissViewControllerAnimated:YES completion:nil];

                             }];

        //Step 3: Add the UIAlertAction ok that we just created to our AlertController
        [userInfoCheck addAction: ok];

        //Step 4: Present the alert to the user
        [self presentViewController:userInfoCheck animated:YES completion:nil];
        return;
    }

    TenderListView *destViewController = segue.destinationViewController;
    destViewController.tenderListViewAmountToPayStr = _transactionListViewUberTotalSumLbl.text;
}

Answer 1

您无法在 prepareForSegue 中呈现 View Controller (例如 UIAlertController)。此时，segue 已提交，您无法更改 View 呈现。

为了执行验证、显示警报并可能取消导航，您应该实现 shouldPerformSegueWithIdentifier