刚开始使用Xcode 4.5，我在控制台得到了这个错误:
警告:试图在< ViewController: 0x1ec3e000>上显示< finishViewController: 0x1e56e0a0 >，其视图不在窗口层次结构中!
视图仍在显示，应用程序中的一切都在正常工作。这是iOS 6的新功能吗?
这是我用来在视图之间更改的代码:
UIStoryboard *storyboard = self.storyboard;
finishViewController *finished =
[storyboard instantiateViewControllerWithIdentifier:@"finishViewController"];
[self presentViewController:finished animated:NO completion:NULL];
当前回答
在主窗口中，可能总是会出现与显示警报不兼容的过渡。为了允许在应用程序生命周期的任何时候显示警报，您应该有一个单独的窗口来完成这项工作。
/// independant window for alerts
@interface AlertWindow: UIWindow
+ (void)presentAlertWithTitle:(NSString *)title message:(NSString *)message;
@end
@implementation AlertWindow
+ (AlertWindow *)sharedInstance
{
static AlertWindow *sharedInstance;
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
sharedInstance = [[AlertWindow alloc] initWithFrame:UIScreen.mainScreen.bounds];
});
return sharedInstance;
}
+ (void)presentAlertWithTitle:(NSString *)title message:(NSString *)message
{
// Using a separate window to solve "Warning: Attempt to present <UIAlertController> on <UIViewController> whose view is not in the window hierarchy!"
UIWindow *shared = AlertWindow.sharedInstance;
shared.userInteractionEnabled = YES;
UIViewController *root = shared.rootViewController;
UIAlertController *alert = [UIAlertController alertControllerWithTitle:title message:message preferredStyle:UIAlertControllerStyleAlert];
alert.modalInPopover = true;
[alert addAction:[UIAlertAction actionWithTitle:@"OK" style:UIAlertActionStyleCancel handler:^(UIAlertAction *action) {
shared.userInteractionEnabled = NO;
[root dismissViewControllerAnimated:YES completion:nil];
}]];
[root presentViewController:alert animated:YES completion:nil];
}
- (instancetype)initWithFrame:(CGRect)frame
{
self = [super initWithFrame:frame];
self.userInteractionEnabled = NO;
self.windowLevel = CGFLOAT_MAX;
self.backgroundColor = UIColor.clearColor;
self.hidden = NO;
self.rootViewController = UIViewController.new;
[NSNotificationCenter.defaultCenter addObserver:self
selector:@selector(bringWindowToTop:)
name:UIWindowDidBecomeVisibleNotification
object:nil];
return self;
}
/// Bring AlertWindow to top when another window is being shown.
- (void)bringWindowToTop:(NSNotification *)notification {
if (![notification.object isKindOfClass:[AlertWindow class]]) {
self.hidden = YES;
self.hidden = NO;
}
}
@end
在设计上总是成功的基本用法:
[AlertWindow presentAlertWithTitle:@"My title" message:@"My message"];
其他回答
我在Swift 4.2上也有类似的问题，但我的观点没有从视图周期中呈现出来。我发现我有多个segue要同时呈现。所以我使用dispatchAsyncAfter。
func updateView() {
DispatchQueue.main.asyncAfter(deadline: .now() + 0.1) { [weak self] in
// for programmatically presenting view controller
// present(viewController, animated: true, completion: nil)
//For Story board segue. you will also have to setup prepare segue for this to work.
self?.performSegue(withIdentifier: "Identifier", sender: nil)
}
}
它工作得很好，试试这个。链接
UIViewController *top = [UIApplication sharedApplication].keyWindow.rootViewController;
[top presentViewController:secondView animated:YES completion: nil];
我也有同样的问题。问题是，performSegueWithIdentifier是由通知触发的，只要我把通知放在主线程上，警告消息就消失了。
Swift 5 -后台线程
如果一个警报控制器在后台线程上执行，那么“Attempt to present…”“其视图不在窗口层次结构中”的错误可能会发生。
所以这个:
present(alert, animated: true, completion: nil)
是这样固定的:
DispatchQueue.main.async { [weak self] in
self?.present(alert, animated: true, completion: nil)
}
我发现故事板中的segue有点坏了。删除segue(并再次创建完全相同的segue)解决了这个问题。
