无法在UIViewControllers视图中找到正确的位置

Question

如果与后端服务器没有连接，我正在尝试实施“通知”。

现在，我有一个ExceptionManager，它生成一个我想在当前viewControllers视图上显示的UIView。但是当我尝试以下面这样的方式进行操作时，它会将视图置于viewController视图的顶部但不考虑导航栏。

如何在我的应用中的自定义视图上将视图放在navigationBar下面？

- (void)showNoConnectionMessage
{
    UIViewController *currentController = [ExceptionManager getTopController];
    UIView *currentView = currentController.view;

    ExceptionMessageVC *exceptionMessageVC = [[ExceptionMessageVC alloc] initWithMessage:@"No connection!"];
    exceptionMessageVC.view.translatesAutoresizingMaskIntoConstraints = NO;

    [currentView addSubview:exceptionMessageVC.view];

    [currentView addConstraint:[NSLayoutConstraint constraintWithItem:exceptionMessageVC.view attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:currentView attribute:NSLayoutAttributeHeight multiplier:0.1f constant:0]];
    [currentView addConstraint:[NSLayoutConstraint constraintWithItem:exceptionMessageVC.view attribute:NSLayoutAttributeWidth relatedBy:NSLayoutRelationEqual toItem:currentView attribute:NSLayoutAttributeWidth multiplier:1.f constant:0]];

    [currentView addConstraint:[NSLayoutConstraint constraintWithItem:exceptionMessageVC.view attribute:NSLayoutAttributeCenterX relatedBy:NSLayoutRelationEqual toItem:currentView attribute:NSLayoutAttributeCenterX multiplier:1.0f constant:0]];
    [currentView addConstraint:[NSLayoutConstraint constraintWithItem:exceptionMessageVC.view attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual toItem:currentView attribute:NSLayoutAttributeTop multiplier:1.0f constant:0]];
}

+ (UIViewController*) getTopController
{
    UIViewController *topViewController = [UIApplication sharedApplication].keyWindow.rootViewController;

    while (topViewController.presentedViewController) {
        topViewController = topViewController.presentedViewController;
    }
    return topViewController;
}

Answer 1

使用约束时，您可以使用topLayoutGuide的{​​{1}}和bottomLayoutGuide属性。他们考虑了导航栏和底栏。

而不是：

UIViewController

这样做：

[currentView addConstraint:[NSLayoutConstraint constraintWithItem:exceptionMessageVC.view attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual toItem:currentView attribute:NSLayoutAttributeTop multiplier:1.0f constant:0]];

Answer 2

添加您的视图：

[[UIApplication sharedApplication].delegate.window addSubview:exceptionMessageVC.view];

Answer 3

通过修改getTopController来解决它：

+ (UIViewController *)getTopController
{
    UIViewController *topViewController = [UIApplication sharedApplication].keyWindow.rootViewController;

    if ([topViewController.childViewControllers.lastObject isKindOfClass:[UITabBarController class]])
    {
        topViewController = ((UITabBarController *) topViewController.childViewControllers.lastObject).selectedViewController;
    }

    if (topViewController.childViewControllers.lastObject)
        topViewController = topViewController.childViewControllers.lastObject;

    while (topViewController.presentedViewController)
    {
        topViewController = topViewController.presentedViewController;
    }
    return topViewController;
}