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
更新到与iOS 13场景，打破了新的UIWindow方法。斯威夫特5.1。
fileprivate var alertWindows = [UIAlertController:UIWindow]()
extension UIAlertController {
func presentInNewWindow(animated: Bool, completion: (() -> Void)?) {
let foregroundActiveScene = UIApplication.shared.connectedScenes.filter { $0.activationState == .foregroundActive }.first
guard let foregroundWindowScene = foregroundActiveScene as? UIWindowScene else { return }
let window = UIWindow(windowScene: foregroundWindowScene)
alertWindows[self] = window
window.rootViewController = UIViewController()
window.windowLevel = .alert + 1
window.makeKeyAndVisible()
window.rootViewController!.present( self, animated: animated, completion: completion)
}
open override func viewDidDisappear(_ animated: Bool) {
super.viewDidDisappear(animated)
alertWindows[self] = nil
}
}
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。
斯威夫特 4+
解决方案我使用多年没有任何问题。首先，我扩展UIWindow来找到它的visibleViewController。注意:如果您使用自定义集合*类(如侧菜单)，您应该在以下扩展中为这种情况添加处理程序。在获得top most视图控制器后，很容易呈现UIAlertController，就像UIAlertView一样。
extension UIAlertController {
func show(animated: Bool = true, completion: (() -> Void)? = nil) {
if let visibleViewController = UIApplication.shared.keyWindow?.visibleViewController {
visibleViewController.present(self, animated: animated, completion: completion)
}
}
}
extension UIWindow {
var visibleViewController: UIViewController? {
guard let rootViewController = rootViewController else {
return nil
}
return visibleViewController(for: rootViewController)
}
private func visibleViewController(for controller: UIViewController) -> UIViewController {
var nextOnStackViewController: UIViewController? = nil
if let presented = controller.presentedViewController {
nextOnStackViewController = presented
} else if let navigationController = controller as? UINavigationController,
let visible = navigationController.visibleViewController {
nextOnStackViewController = visible
} else if let tabBarController = controller as? UITabBarController,
let visible = (tabBarController.selectedViewController ??
tabBarController.presentedViewController) {
nextOnStackViewController = visible
}
if let nextOnStackViewController = nextOnStackViewController {
return visibleViewController(for: nextOnStackViewController)
} else {
return controller
}
}
}
如果有人感兴趣，我创建了一个Swift 3版本的@agilityvision答案。代码:
import Foundation
import UIKit
extension UIAlertController {
var window: UIWindow? {
get {
return objc_getAssociatedObject(self, "window") as? UIWindow
}
set {
objc_setAssociatedObject(self, "window", newValue, objc_AssociationPolicy.OBJC_ASSOCIATION_RETAIN_NONATOMIC)
}
}
open override func viewDidDisappear(_ animated: Bool) {
super.viewDidDisappear(animated)
self.window?.isHidden = true
self.window = nil
}
func show(animated: Bool = true) {
let window = UIWindow(frame: UIScreen.main.bounds)
window.rootViewController = UIViewController(nibName: nil, bundle: nil)
let delegate = UIApplication.shared.delegate
if delegate?.window != nil {
window.tintColor = delegate!.window!!.tintColor
}
window.windowLevel = UIApplication.shared.windows.last!.windowLevel + 1
window.makeKeyAndVisible()
window.rootViewController!.present(self, animated: animated, completion: nil)
self.window = window
}
}
你可以将当前视图或控制器作为参数发送:
+ (void)myUtilityMethod:(id)controller {
// do stuff
// something bad happened, display an alert.
}
在Swift 3中
let alertLogin = UIAlertController.init(title: "Your Title", message:"Your message", preferredStyle: .alert)
alertLogin.addAction(UIAlertAction(title: "Done", style:.default, handler: { (AlertAction) in
}))
self.window?.rootViewController?.present(alertLogin, animated: true, completion: nil)
