场景:用户点击视图控制器上的按钮。视图控制器是导航堆栈中最顶层的(很明显)。tap调用在另一个类上调用的实用程序类方法。这里发生了不好的事情我想在控件返回到视图控制器之前在那里显示一个警告。
+ (void)myUtilityMethod {
// do stuff
// something bad happened, display an alert.
}
这是可能的UIAlertView(但可能不太合适)。
在这种情况下，你如何在myUtilityMethod中呈现UIAlertController ?
当前回答
@agilityvision的答案翻译为Swift4/iOS11。我没有使用本地化字符串，但你可以很容易地改变:
import UIKit
/** An alert controller that can be called without a view controller.
Creates a blank view controller and presents itself over that
**/
class AlertPlusViewController: UIAlertController {
private var alertWindow: UIWindow?
override func viewDidLoad() {
super.viewDidLoad()
}
override func viewDidDisappear(_ animated: Bool) {
super.viewDidDisappear(animated)
self.alertWindow?.isHidden = true
alertWindow = nil
}
func show() {
self.showAnimated(animated: true)
}
func showAnimated(animated _: Bool) {
let blankViewController = UIViewController()
blankViewController.view.backgroundColor = UIColor.clear
let window = UIWindow(frame: UIScreen.main.bounds)
window.rootViewController = blankViewController
window.backgroundColor = UIColor.clear
window.windowLevel = UIWindowLevelAlert + 1
window.makeKeyAndVisible()
self.alertWindow = window
blankViewController.present(self, animated: true, completion: nil)
}
func presentOkayAlertWithTitle(title: String?, message: String?) {
let alertController = AlertPlusViewController(title: title, message: message, preferredStyle: .alert)
let okayAction = UIAlertAction(title: "Ok", style: .default, handler: nil)
alertController.addAction(okayAction)
alertController.show()
}
func presentOkayAlertWithError(error: NSError?) {
let title = "Error"
let message = error?.localizedDescription
presentOkayAlertWithTitle(title: title, message: message)
}
}
其他回答
在调用类方法之前注册通知。
斯威夫特代码:
NSNotificationCenter.defaultCenter().addObserver(self, selector: "displayAlert", name: "ErrorOccured", object: nil)
在displayAlert实例方法中，您可以显示警报。
这在Swift中适用于普通的视图控制器，即使屏幕上有一个导航控制器:
let alert = UIAlertController(...)
let alertWindow = UIWindow(frame: UIScreen.main.bounds)
alertWindow.rootViewController = UIViewController()
alertWindow.windowLevel = UIWindowLevelAlert + 1;
alertWindow.makeKeyAndVisible()
alertWindow.rootViewController?.presentViewController(alert, animated: true, completion: nil)
Kevin Sliech提供了一个很好的解决方案。
我现在在我的主UIViewController子类中使用下面的代码。
我做的一个小改动是检查最好的表示控制器是不是一个普通的UIViewController。如果不是，那就一定是某个VC表示一个普通VC。因此，我们返回正在呈现的VC。
- (UIViewController *)bestPresentationController
{
UIViewController *bestPresentationController = [UIApplication sharedApplication].keyWindow.rootViewController;
if (![bestPresentationController isMemberOfClass:[UIViewController class]])
{
bestPresentationController = bestPresentationController.presentedViewController;
}
return bestPresentationController;
}
在我的测试中似乎一切正常。
谢谢你，凯文!
我尝试了上面提到的所有方法，但都没有成功。我在Swift 3.0中使用的方法:
extension UIAlertController {
func show() {
present(animated: true, completion: nil)
}
func present(animated: Bool, completion: (() -> Void)?) {
if var topController = UIApplication.shared.keyWindow?.rootViewController {
while let presentedViewController = topController.presentedViewController {
topController = presentedViewController
}
topController.present(self, animated: animated, completion: completion)
}
}
}
斯威夫特
let alertController = UIAlertController(title: "title", message: "message", preferredStyle: .alert)
//...
var rootViewController = UIApplication.shared.keyWindow?.rootViewController
if let navigationController = rootViewController as? UINavigationController {
rootViewController = navigationController.viewControllers.first
}
if let tabBarController = rootViewController as? UITabBarController {
rootViewController = tabBarController.selectedViewController
}
//...
rootViewController?.present(alertController, animated: true, completion: nil)
objective - c
UIAlertController *alertController = [UIAlertController alertControllerWithTitle:@"Title" message:@"message" preferredStyle:UIAlertControllerStyleAlert];
//...
id rootViewController = [UIApplication sharedApplication].delegate.window.rootViewController;
if([rootViewController isKindOfClass:[UINavigationController class]])
{
rootViewController = ((UINavigationController *)rootViewController).viewControllers.firstObject;
}
if([rootViewController isKindOfClass:[UITabBarController class]])
{
rootViewController = ((UITabBarController *)rootViewController).selectedViewController;
}
//...
[rootViewController presentViewController:alertController animated:YES completion:nil];
