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的最顶层（显然）。点击调用在另一个类上调用的实用程序类方法。那里发生了一件坏事，我想在控制返回视图控制器之前在那里显示一个警报。
+ (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，你如何呈现一个UIAlertController, 就在那里myUtilityMethod？
在 WWDC，我在其中一个实验室停下来，问了一位 Apple 工程师同样的问题：“显示 的最佳做法是UIAlertController什么？” 他说他们经常收到这个问题，我们开玩笑说他们应该就这个问题进行一次会议。他说，苹果内部正在创建UIWindow一个透明的UIViewController，然后UIAlertController在上面呈现。基本上迪伦·贝特曼的回答是什么。
但我不想使用的子类，UIAlertController因为这需要我在整个应用程序中更改我的代码。因此，在关联对象的帮助下，我创建了一个类别UIAlertController，提供了showObjective-C 中的方法。
以下是相关代码：
#import "UIAlertController+Window.h"
#import <objc/runtime.h>
@interface UIAlertController (Window)
- (void)show;
- (void)show:(BOOL)animated;
@end
@interface UIAlertController (Private)
@property (nonatomic, strong) UIWindow *alertWindow;
@end
@implementation UIAlertController (Private)
@dynamic alertWindow;
- (void)setAlertWindow:(UIWindow *)alertWindow {
objc_setAssociatedObject(self, @selector(alertWindow), alertWindow, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}
- (UIWindow *)alertWindow {
return objc_getAssociatedObject(self, @selector(alertWindow));
}
@end
@implementation UIAlertController (Window)
- (void)show {
[self show:YES];
}
- (void)show:(BOOL)animated {
self.alertWindow = [[UIWindow alloc] initWithFrame:[UIScreen mainScreen].bounds];
self.alertWindow.rootViewController = [[UIViewController alloc] init];
id<UIApplicationDelegate> delegate = [UIApplication sharedApplication].delegate;
// Applications that does not load with UIMainStoryboardFile might not have a window property:
if ([delegate respondsToSelector:@selector(window)]) {
// we inherit the main window's tintColor
self.alertWindow.tintColor = delegate.window.tintColor;
}
// window level is above the top window (this makes the alert, if it's a sheet, show over the keyboard)
UIWindow *topWindow = [UIApplication sharedApplication].windows.lastObject;
self.alertWindow.windowLevel = topWindow.windowLevel + 1;
[self.alertWindow makeKeyAndVisible];
[self.alertWindow.rootViewController presentViewController:self animated:animated completion:nil];
}
- (void)viewDidDisappear:(BOOL)animated {
[super viewDidDisappear:animated];
// precaution to ensure window gets destroyed
self.alertWindow.hidden = YES;
self.alertWindow = nil;
}
@end
这是一个示例用法：
// need local variable for TextField to prevent retain cycle of Alert otherwise UIWindow
// would not disappear after the Alert was dismissed
__block UITextField *localTextField;
UIAlertController *alert = [UIAlertController alertControllerWithTitle:@"Global Alert" message:@"Enter some text" preferredStyle:UIAlertControllerStyleAlert];
[alert addAction:[UIAlertAction actionWithTitle:@"OK" style:UIAlertActionStyleDefault handler:^(UIAlertAction *action) {
NSLog(@"do something with text:%@", localTextField.text);
// do NOT use alert.textfields or otherwise reference the alert in the block. Will cause retain cycle
}]];
[alert addTextFieldWithConfigurationHandler:^(UITextField *textField) {
localTextField = textField;
}];
[alert show];
释放 时，创建的UIWindow将被销毁UIAlertController，因为它是唯一保留UIWindow. 但是，如果您将 分配UIAlertController给某个属性或通过访问其中一个操作块中的警报来增加其保留计数，则UIWindow将保留在屏幕上，从而锁定您的 UI。在需要访问的情况下，请参阅上面的示例使用代码以避免UITextField.
我用一个测试项目制作了一个 GitHub 存储库：FFGlobalAlertController
迅速
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];
您可以使用 Swift 2.2 执行以下操作：
let alertController: UIAlertController = ...
UIApplication.sharedApplication().keyWindow?.rootViewController?.presentViewController(alertController, animated: true, completion: nil)
和斯威夫特 3.0：
let alertController: UIAlertController = ...
UIApplication.shared.keyWindow?.rootViewController?.present(alertController, animated: true, completion: nil)
几个月前我发布了一个类似的问题，并认为我终于解决了这个问题。如果您只想查看代码，请点击我帖子底部的链接。
解决方案是使用额外的 UIWindow。
当你想显示你的 UIAlertController 时：
window.makeKeyAndVisible())window.rootViewController = UIViewController())有几点需要注意：
window.windowLevel = UIWindowLevelAlert + 1)最后，如果您只想看一下，我有一个完整的实现。
对于和/或UIAlertController extension的所有情况都非常通用。如果此时屏幕上有模态 VC，也可以使用。 UINavigationControllerUITabBarController
用法：
//option 1:
myAlertController.show()
//option 2:
myAlertController.present(animated: true) {
//completion code...
}
这是扩展：
//Uses Swift1.2 syntax with the new if-let
// so it won't compile on a lower version.
extension UIAlertController {
func show() {
present(animated: true, completion: nil)
}
func present(#animated: Bool, completion: (() -> Void)?) {
if let rootVC = UIApplication.sharedApplication().keyWindow?.rootViewController {
presentFromController(rootVC, animated: animated, completion: completion)
}
}
private func presentFromController(controller: UIViewController, animated: Bool, completion: (() -> Void)?) {
if let navVC = controller as? UINavigationController,
let visibleVC = navVC.visibleViewController {
presentFromController(visibleVC, animated: animated, completion: completion)
} else {
if let tabVC = controller as? UITabBarController,
let selectedVC = tabVC.selectedViewController {
presentFromController(selectedVC, animated: animated, completion: completion)
} else {
controller.presentViewController(self, animated: animated, completion: completion)
}
}
}
}
改进agilityvision 的答案，您需要创建一个带有透明根视图控制器的窗口，并从那里显示警报视图。
但是，只要您在警报控制器中有一个操作，您就不需要保留对 window 的引用。作为动作处理程序块的最后一步，您只需要隐藏窗口作为清理任务的一部分。通过在处理程序块中引用窗口，这会创建一个临时循环引用，一旦警报控制器被解除，该引用就会被破坏。
UIWindow* window = [[UIWindow alloc] initWithFrame:[UIScreen mainScreen].bounds];
window.rootViewController = [UIViewController new];
window.windowLevel = UIWindowLevelAlert + 1;
UIAlertController* alertCtrl = [UIAlertController alertControllerWithTitle:... message:... preferredStyle:UIAlertControllerStyleAlert];
[alertCtrl addAction:[UIAlertAction actionWithTitle:NSLocalizedString(@"OK",@"Generic confirm") style:UIAlertActionStyleCancel handler:^(UIAlertAction * _Nonnull action) {
... // do your stuff
// very important to hide the window afterwards.
// this also keeps a reference to the window until the action is invoked.
window.hidden = YES;
}]];
[window makeKeyAndVisible];
[window.rootViewController presentViewController:alertCtrl animated:YES completion:nil];
以下解决方案不起作用，即使它在所有版本中看起来都非常有希望。此解决方案正在生成 WARNING。
警告：尝试呈现不在窗口层次结构中的视图！
https://stackoverflow.com/a/34487871/2369867 => 这看起来很有希望。但它不在。Swift 3所以我在 Swift 3 中回答这个问题，这不是模板示例。
一旦您粘贴到任何函数中，这本身就是功能齐全的代码。
快速
Swift 3自包含代码
let alertController = UIAlertController(title: "<your title>", message: "<your message>", preferredStyle: UIAlertControllerStyle.alert)
alertController.addAction(UIAlertAction(title: "Close", style: UIAlertActionStyle.cancel, handler: nil))
let alertWindow = UIWindow(frame: UIScreen.main.bounds)
alertWindow.rootViewController = UIViewController()
alertWindow.windowLevel = UIWindowLevelAlert + 1;
alertWindow.makeKeyAndVisible()
alertWindow.rootViewController?.present(alertController, animated: true, completion: nil)
这是在 Swift 3 中经过测试和工作的代码。
这是mythicalcoder的答案作为扩展，在Swift 4中测试和工作：
extension UIAlertController {
func presentInOwnWindow(animated: Bool, completion: (() -> Void)?) {
let alertWindow = UIWindow(frame: UIScreen.main.bounds)
alertWindow.rootViewController = UIViewController()
alertWindow.windowLevel = UIWindowLevelAlert + 1
alertWindow.makeKeyAndVisible()
alertWindow.rootViewController?.present(self, animated: animated, completion: completion)
}
}
示例用法：
let alertController = UIAlertController(title: "<Alert Title>", message: "<Alert Message>", preferredStyle: .alert)
alertController.addAction(UIAlertAction(title: "Close", style: .cancel, handler: nil))
alertController.presentInOwnWindow(animated: true, completion: {
print("completed")
})
这在 Swift 中适用于普通视图控制器，即使屏幕上有导航控制器：
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)
添加到 Zev 的答案（并切换回 Objective-C），您可能会遇到这样一种情况，即您的根视图控制器正在通过 segue 或其他方式呈现一些其他 VC。在根 VC 上调用 presentViewController 会处理这个问题：
[[UIApplication sharedApplication].keyWindow.rootViewController.presentedViewController presentViewController:alertController animated:YES completion:^{}];
这解决了我在根 VC 连接到另一个 VC 时遇到的问题，并且没有显示警报控制器，而是发出了类似于上面报告的警告：
Warning: Attempt to present <UIAlertController: 0x145bfa30> on <UINavigationController: 0x1458e450> whose view is not in the window hierarchy!
我还没有测试过，但是如果你的根 VC 恰好是一个导航控制器，这也可能是必要的。
显示消息后隐藏窗口很重要。
func showErrorMessage(_ message: String) {
let alertWindow = UIWindow(frame: UIScreen.main.bounds)
alertWindow.rootViewController = UIViewController()
let alertController = UIAlertController(title: "Error", message: message, preferredStyle: UIAlertController.Style.alert)
alertController.addAction(UIAlertAction(title: "Close", style: UIAlertAction.Style.cancel, handler: { _ in
alertWindow.isHidden = true
}))
alertWindow.windowLevel = UIWindow.Level.alert + 1;
alertWindow.makeKeyAndVisible()
alertWindow.rootViewController?.present(alertController, animated: true, completion: nil)
}
@agilityvision 的答案翻译为 Swift4/iOS11。我没有使用本地化字符串，但您可以轻松更改：
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)
}
}
对于 iOS 13，以 mythicalcoder 和 bobbyrehm 的答案为基础：
在 iOS 13 中，如果您正在创建自己的窗口来显示警报，则需要持有对该窗口的强引用，否则您的警报将不会显示，因为当其引用退出范围时，该窗口将立即被释放。
此外，您需要在解除警报后再次将引用设置为 nil，以便删除窗口以继续允许用户在其下方的主窗口上进行交互。
您可以创建一个UIViewController子类来封装窗口内存管理逻辑：
class WindowAlertPresentationController: UIViewController {
// MARK: - Properties
private lazy var window: UIWindow? = UIWindow(frame: UIScreen.main.bounds)
private let alert: UIAlertController
// MARK: - Initialization
init(alert: UIAlertController) {
self.alert = alert
super.init(nibName: nil, bundle: nil)
}
required init?(coder aDecoder: NSCoder) {
fatalError("This initializer is not supported")
}
// MARK: - Presentation
func present(animated: Bool, completion: (() -> Void)?) {
window?.rootViewController = self
window?.windowLevel = UIWindow.Level.alert + 1
window?.makeKeyAndVisible()
present(alert, animated: animated, completion: completion)
}
// MARK: - Overrides
override func dismiss(animated flag: Bool, completion: (() -> Void)? = nil) {
super.dismiss(animated: flag) {
self.window = nil
completion?()
}
}
}
你可以按原样使用它，或者如果你想在你UIAlertController的 .
extension UIAlertController {
func presentInOwnWindow(animated: Bool, completion: (() -> Void)?) {
let windowAlertPresentationController = WindowAlertPresentationController(alert: self)
windowAlertPresentationController.present(animated: animated, completion: completion)
}
}
像 Aviel Gross 的答案一样创建扩展。在这里，您有 Objective-C 扩展。
在这里你有头文件 *.h
// UIAlertController+Showable.h
#import <UIKit/UIKit.h>
@interface UIAlertController (Showable)
- (void)show;
- (void)presentAnimated:(BOOL)animated
completion:(void (^)(void))completion;
- (void)presentFromController:(UIViewController *)viewController
animated:(BOOL)animated
completion:(void (^)(void))completion;
@end
和实施：*.m
// UIAlertController+Showable.m
#import "UIAlertController+Showable.h"
@implementation UIAlertController (Showable)
- (void)show
{
[self presentAnimated:YES completion:nil];
}
- (void)presentAnimated:(BOOL)animated
completion:(void (^)(void))completion
{
UIViewController *rootVC = [UIApplication sharedApplication].keyWindow.rootViewController;
if (rootVC != nil) {
[self presentFromController:rootVC animated:animated completion:completion];
}
}
- (void)presentFromController:(UIViewController *)viewController
animated:(BOOL)animated
completion:(void (^)(void))completion
{
if ([viewController isKindOfClass:[UINavigationController class]]) {
UIViewController *visibleVC = ((UINavigationController *)viewController).visibleViewController;
[self presentFromController:visibleVC animated:animated completion:completion];
} else if ([viewController isKindOfClass:[UITabBarController class]]) {
UIViewController *selectedVC = ((UITabBarController *)viewController).selectedViewController;
[self presentFromController:selectedVC animated:animated completion:completion];
} else {
[viewController presentViewController:self animated:animated completion:completion];
}
}
@end
您在您的实现文件中使用此扩展，如下所示：
#import "UIAlertController+Showable.h"
UIAlertController* alert = [UIAlertController
alertControllerWithTitle:@"Title here"
message:@"Detail message here"
preferredStyle:UIAlertControllerStyleAlert];
UIAlertAction* defaultAction = [UIAlertAction
actionWithTitle:@"OK"
style:UIAlertActionStyleDefault
handler:^(UIAlertAction * action) {}];
[alert addAction:defaultAction];
// Add more actions if needed
[alert show];
斯威夫特 4+
我使用多年的解决方案完全没有问题。首先我扩展UIWindow发现它是visibleViewController。注意：如果您使用自定义集合 * 类（例如侧边菜单），您应该在以下扩展中添加这种情况的处理程序。在获得最顶级的视图控制器后，它很容易呈现UIAlertController，就像UIAlertView.
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
}
}
}
交叉发布我的答案，因为这两个线程没有被标记为骗子......
现在这UIViewController是响应者链的一部分，您可以执行以下操作：
if let vc = self.nextResponder()?.targetForAction(#selector(UIViewController.presentViewController(_:animated:completion:)), withSender: self) as? UIViewController {
let alert = UIAlertController(title: "A snappy title", message: "Something bad happened", preferredStyle: .Alert)
alert.addAction(UIAlertAction(title: "OK", style: .Default, handler: nil))
vc.presentViewController(alert, animated: true, completion: nil)
}
Zev Eisenberg 的回答简单明了，但并不总是有效，并且可能会失败并显示以下警告消息：
Warning: Attempt to present <UIAlertController: 0x7fe6fd951e10>
on <ThisViewController: 0x7fe6fb409480> which is already presenting
<AnotherViewController: 0x7fe6fd109c00>
这是因为 windows rootViewController 不在显示视图的顶部。为了纠正这个问题，我们需要遍历表示链，如我用 Swift 3 编写的 UIAlertController 扩展代码所示：
/// show the alert in a view controller if specified; otherwise show from window's root pree
func show(inViewController: UIViewController?) {
if let vc = inViewController {
vc.present(self, animated: true, completion: nil)
} else {
// find the root, then walk up the chain
var viewController = UIApplication.shared.keyWindow?.rootViewController
var presentedVC = viewController?.presentedViewController
while presentedVC != nil {
viewController = presentedVC
presentedVC = viewController?.presentedViewController
}
// now we present
viewController?.present(self, animated: true, completion: nil)
}
}
func show() {
show(inViewController: nil)
}
2017 年 9 月 15 日更新：
测试并确认，上述逻辑在新推出的 iOS 11 GM 种子中仍然有效。然而，agilityvision 投票最多的方法却没有：新创建的警报视图位于UIWindow键盘下方，可能会阻止用户点击其按钮。这是因为在 iOS 11 中，所有高于键盘窗口的 windowLevels 都会降低到低于它的级别。
呈现的一个伪影是在呈现keyWindow警报时键盘向下滑动的动画，并在解除警报时再次向上滑动。如果您希望键盘在演示期间停留在那里，您可以尝试从顶部窗口本身进行演示，如下面的代码所示：
func show(inViewController: UIViewController?) {
if let vc = inViewController {
vc.present(self, animated: true, completion: nil)
} else {
// get a "solid" window with the highest level
let alertWindow = UIApplication.shared.windows.filter { $0.tintColor != nil || $0.className() == "UIRemoteKeyboardWindow" }.sorted(by: { (w1, w2) -> Bool in
return w1.windowLevel < w2.windowLevel
}).last
// save the top window's tint color
let savedTintColor = alertWindow?.tintColor
alertWindow?.tintColor = UIApplication.shared.keyWindow?.tintColor
// walk up the presentation tree
var viewController = alertWindow?.rootViewController
while viewController?.presentedViewController != nil {
viewController = viewController?.presentedViewController
}
viewController?.present(self, animated: true, completion: nil)
// restore the top window's tint color
if let tintColor = savedTintColor {
alertWindow?.tintColor = tintColor
}
}
}
上述代码唯一不太重要的部分是它检查类名UIRemoteKeyboardWindow以确保我们也可以包含它。尽管如此，上面的代码在 iOS 9、10 和 11 GM 种子中运行良好，具有正确的色调，并且没有键盘滑动伪影。
在 Objective-C 中显示警报的速记方法：
[[[[UIApplication sharedApplication] keyWindow] rootViewController] presentViewController:alertController animated:YES completion:nil];
alertController你的UIAlertController对象在哪里。
注意：您还需要确保您的助手类扩展UIViewController
iOS13 场景支持（使用 UIWindowScene 时）
import UIKit
private var windows: [String:UIWindow] = [:]
extension UIWindowScene {
static var focused: UIWindowScene? {
return UIApplication.shared.connectedScenes
.first { $0.activationState == .foregroundActive && $0 is UIWindowScene } as? UIWindowScene
}
}
class StyledAlertController: UIAlertController {
var wid: String?
func present(animated: Bool, completion: (() -> Void)?) {
//let window = UIWindow(frame: UIScreen.main.bounds)
guard let window = UIWindowScene.focused.map(UIWindow.init(windowScene:)) else {
return
}
window.rootViewController = UIViewController()
window.windowLevel = .alert + 1
window.makeKeyAndVisible()
window.rootViewController!.present(self, animated: animated, completion: completion)
wid = UUID().uuidString
windows[wid!] = window
}
open override func viewDidDisappear(_ animated: Bool) {
super.viewDidDisappear(animated)
if let wid = wid {
windows[wid] = nil
}
}
}
如果有人感兴趣，我创建了一个 Swift 3 版本的 @agilityvision 答案。编码：
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
}
}
其中一些答案仅对我部分有效，将它们组合在 AppDelegate 中的以下类方法中是我的解决方案。它适用于 iPad，在 UITabBarController 视图中，在 UINavigationController 中，在呈现模式时。在 iOS 10 和 13 上测试。
+ (UIViewController *)rootViewController {
UIViewController *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;
if (rootViewController.presentedViewController != nil)
rootViewController = rootViewController.presentedViewController;
return rootViewController;
}
用法：
[[AppDelegate rootViewController] presentViewController ...
更新为与 iOS 13 场景一起使用，这打破了新的 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
}
}
extension UIApplication {
/// The top most view controller
static var topMostViewController: UIViewController? {
return UIApplication.shared.keyWindow?.rootViewController?.visibleViewController
}
}
extension UIViewController {
/// The visible view controller from a given view controller
var visibleViewController: UIViewController? {
if let navigationController = self as? UINavigationController {
return navigationController.topViewController?.visibleViewController
} else if let tabBarController = self as? UITabBarController {
return tabBarController.selectedViewController?.visibleViewController
} else if let presentedViewController = presentedViewController {
return presentedViewController.visibleViewController
} else {
return self
}
}
}
有了这个，你可以像这样轻松地呈现你的警报
UIApplication.topMostViewController?.present(viewController, animated: true, completion: nil)
需要注意的一点是，如果当前正在显示 UIAlertController，UIApplication.topMostViewController将返回一个UIAlertController. 在 a 之上呈现UIAlertController有奇怪的行为，应该避免。因此，您应该!(UIApplication.topMostViewController is UIAlertController)在呈现之前手动检查，或者添加一个else if案例以返回 nil ifself is UIAlertController
extension UIViewController {
/// The visible view controller from a given view controller
var visibleViewController: UIViewController? {
if let navigationController = self as? UINavigationController {
return navigationController.topViewController?.visibleViewController
} else if let tabBarController = self as? UITabBarController {
return tabBarController.selectedViewController?.visibleViewController
} else if let presentedViewController = presentedViewController {
return presentedViewController.visibleViewController
} else if self is UIAlertController {
return nil
} else {
return self
}
}
}
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演示控制器是否不是普通的 UIViewController。如果不是，那一定是某个 VC 提供了一个普通的 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;
}
到目前为止，在我的测试中似乎一切正常。
谢谢凯文！
您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.
}
除了给出很好的答案（agilityvision，adib，malhal）。要达到类似旧 UIAlertViews 中的排队行为（避免警报窗口重叠），请使用此块来观察窗口级别的可用性：
@interface UIWindow (WLWindowLevel)
+ (void)notifyWindowLevelIsAvailable:(UIWindowLevel)level withBlock:(void (^)())block;
@end
@implementation UIWindow (WLWindowLevel)
+ (void)notifyWindowLevelIsAvailable:(UIWindowLevel)level withBlock:(void (^)())block {
UIWindow *keyWindow = [UIApplication sharedApplication].keyWindow;
if (keyWindow.windowLevel == level) {
// window level is occupied, listen for windows to hide
id observer;
observer = [[NSNotificationCenter defaultCenter] addObserverForName:UIWindowDidBecomeHiddenNotification object:keyWindow queue:nil usingBlock:^(NSNotification *note) {
[[NSNotificationCenter defaultCenter] removeObserver:observer];
[self notifyWindowLevelIsAvailable:level withBlock:block]; // recursive retry
}];
} else {
block(); // window level is available
}
}
@end
完整示例：
[UIWindow notifyWindowLevelIsAvailable:UIWindowLevelAlert withBlock:^{
UIWindow *alertWindow = [[UIWindow alloc] initWithFrame:[UIScreen mainScreen].bounds];
alertWindow.windowLevel = UIWindowLevelAlert;
alertWindow.rootViewController = [UIViewController new];
[alertWindow makeKeyAndVisible];
UIAlertController *alertController = [UIAlertController alertControllerWithTitle:@"Alert" message:nil preferredStyle:UIAlertControllerStyleAlert];
[alertController addAction:[UIAlertAction actionWithTitle:@"OK" style:UIAlertActionStyleCancel handler:^(UIAlertAction *action) {
alertWindow.hidden = YES;
}]];
[alertWindow.rootViewController presentViewController:alertController animated:YES completion:nil];
}];
这将允许您避免警报窗口重叠。可以使用相同的方法为任意数量的窗口层分离和放入队列视图控制器。
似乎工作：
static UIViewController *viewControllerForView(UIView *view) {
UIResponder *responder = view;
do {
responder = [responder nextResponder];
}
while (responder && ![responder isKindOfClass:[UIViewController class]]);
return (UIViewController *)responder;
}
-(void)showActionSheet {
UIAlertController *alertController = [UIAlertController alertControllerWithTitle:nil message:nil preferredStyle:UIAlertControllerStyleActionSheet];
[alertController addAction:[UIAlertAction actionWithTitle:@"Cancel" style:UIAlertActionStyleCancel handler:nil]];
[alertController addAction:[UIAlertAction actionWithTitle:@"Do it" style:UIAlertActionStyleDefault handler:nil]];
[viewControllerForView(self) presentViewController:alertController animated:YES completion:nil];
}
我尝试了所有提到的，但没有成功。我用于 Swift 3.0 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)
}
}
}
另外的选择：
var topController:UIViewController = UIApplication.shared.keyWindow!.rootViewController!
while ((topController.presentedViewController) != nil) {
topController = topController.presentedViewController!
}
topController.present(alert, animated:true, completion:nil)
您可以尝试UIViewController使用诸如
- (void)presentErrorMessage;And 之类的方法实现一个类别，并在该方法中实现 UIAlertController，然后将其呈现在self. 比在您的客户端代码中，您将拥有以下内容：
[myViewController presentErrorMessage];
这样，您将避免不必要的参数和有关视图不在窗口层次结构中的警告。
创建助手类 AlertWindow 并用作
let alertWindow = AlertWindow();
let alert = UIAlertController(title: "Hello", message: "message", preferredStyle: .alert);
let cancel = UIAlertAction(title: "Ok", style: .cancel){(action) in
//.... action code here
// reference to alertWindow retain it. Every action must have this at end
alertWindow.isHidden = true;
// here AlertWindow.deinit{ }
}
alert.addAction(cancel);
alertWindow.present(alert, animated: true, completion: nil)
class AlertWindow:UIWindow{
convenience init(){
self.init(frame:UIScreen.main.bounds);
}
override init(frame: CGRect) {
super.init(frame: frame);
if let color = UIApplication.shared.delegate?.window??.tintColor {
tintColor = color;
}
rootViewController = UIViewController()
windowLevel = UIWindowLevelAlert + 1;
makeKeyAndVisible()
}
required init?(coder aDecoder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
deinit{
// semaphor.signal();
}
func present(_ ctrl:UIViewController, animated:Bool, completion: (()->Void)?){
rootViewController!.present(ctrl, animated: animated, completion: completion);
}
}
我知道这是针对 iOS 的，因为搜索引擎中的几乎所有链接都可以找到 iOS 帖子，所以我想我会将其提供给 macOS 开发人员。
macOS 上的 Swift 5.5
我根据 Darkngs 的回答将此添加到另一个类中的一个方法中：
let alert = NSAlert()
let viewController = NSApplication.shared.keyWindow?.contentViewController
alert.messageText = "An Alert Message."
alert.addButton(withTitle: "Ok")
alert.beginSheetModal(for: (viewController?.view.window)!) {
(returnCode: NSApplication.ModalResponse) -> Void in
}
@agilityvision 的回答太好了。我在 swift 项目中使用过，所以我想我会使用 swift 3.0 分享我对他的回答的看法
fileprivate class MyUIAlertController: UIAlertController {
typealias Handler = () -> Void
struct AssociatedKeys {
static var alertWindowKey = "alertWindowKey"
}
dynamic var _alertWindow: UIWindow?
var alertWindow: UIWindow? {
return objc_getAssociatedObject(self, &AssociatedKeys.alertWindowKey) as? UIWindow
}
func setAlert(inWindow window: UIWindow) {
objc_setAssociatedObject(self, &AssociatedKeys.alertWindowKey, _alertWindow, .OBJC_ASSOCIATION_RETAIN_NONATOMIC)
}
func show(completion: Handler? = nil) {
show(animated: true, completion: completion)
}
func show(animated: Bool, completion: Handler? = nil) {
_alertWindow = UIWindow(frame: UIScreen.main.bounds)
_alertWindow?.rootViewController = UIViewController()
if let delegate: UIApplicationDelegate = UIApplication.shared.delegate, let window = delegate.window {
_alertWindow?.tintColor = window?.tintColor
}
let topWindow = UIApplication.shared.windows.last
_alertWindow?.windowLevel = topWindow?.windowLevel ?? 0 + 1
_alertWindow?.makeKeyAndVisible()
_alertWindow?.rootViewController?.present(self, animated: animated, completion: completion)
}
fileprivate override func viewDidDisappear(_ animated: Bool) {
super.viewDidDisappear(animated)
_alertWindow?.isHidden = true
_alertWindow = nil
}
}
您可以使用 2 种方法：
- 改为使用UIAlertView或“UIActionSheet”（不推荐，因为它在 iOS 8 中已弃用，但现在可以使用）
- 以某种方式记住呈现的最后一个视图控制器。这是示例。
@interface UIViewController (TopController)
+ (UIViewController *)topViewController;
@end
// implementation
#import "UIViewController+TopController.h"
#import <objc/runtime.h>
static __weak UIViewController *_topViewController = nil;
@implementation UIViewController (TopController)
+ (UIViewController *)topViewController {
UIViewController *vc = _topViewController;
while (vc.parentViewController) {
vc = vc.parentViewController;
}
return vc;
}
+ (void)load {
[super load];
[self swizzleSelector:@selector(viewDidAppear:) withSelector:@selector(myViewDidAppear:)];
[self swizzleSelector:@selector(viewWillDisappear:) withSelector:@selector(myViewWillDisappear:)];
}
- (void)myViewDidAppear:(BOOL)animated {
if (_topViewController == nil) {
_topViewController = self;
}
[self myViewDidAppear:animated];
}
- (void)myViewWillDisappear:(BOOL)animated {
if (_topViewController == self) {
_topViewController = nil;
}
[self myViewWillDisappear:animated];
}
+ (void)swizzleSelector:(SEL)sel1 withSelector:(SEL)sel2
{
Class class = [self class];
Method originalMethod = class_getInstanceMethod(class, sel1);
Method swizzledMethod = class_getInstanceMethod(class, sel2);
BOOL didAddMethod = class_addMethod(class,
sel1,
method_getImplementation(swizzledMethod),
method_getTypeEncoding(swizzledMethod));
if (didAddMethod) {
class_replaceMethod(class,
sel2,
method_getImplementation(originalMethod),
method_getTypeEncoding(originalMethod));
} else {
method_exchangeImplementations(originalMethod, swizzledMethod);
}
}
@end
用法：
[[UIViewController topViewController] presentViewController:alertController ...];
在斯威夫特 3
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)
我在我的 AppDelegate 类中使用了这个代码，并带有一些小的个人变化
-(UIViewController*)presentingRootViewController
{
UIViewController *vc = self.window.rootViewController;
if ([vc isKindOfClass:[UINavigationController class]] ||
[vc isKindOfClass:[UITabBarController class]])
{
// filter nav controller
vc = [AppDelegate findChildThatIsNotNavController:vc];
// filter tab controller
if ([vc isKindOfClass:[UITabBarController class]]) {
UITabBarController *tbc = ((UITabBarController*)vc);
if ([tbc viewControllers].count > 0) {
vc = [tbc viewControllers][tbc.selectedIndex];
// filter nav controller again
vc = [AppDelegate findChildThatIsNotNavController:vc];
}
}
}
return vc;
}
/**
* Private helper
*/
+(UIViewController*)findChildThatIsNotNavController:(UIViewController*)vc
{
if ([vc isKindOfClass:[UINavigationController class]]) {
if (((UINavigationController *)vc).viewControllers.count > 0) {
vc = [((UINavigationController *)vc).viewControllers objectAtIndex:0];
}
}
return vc;
}
斯威夫特 5
我刚刚创建了一个新窗口并在其中添加了警报视图控制器。
检查我的班级 TopViewController：
https://gist.github.com/odnaks/3f3fd0d20f318c6276e76d0f9d7de5a7
我用的很简单，比如 UIAlertController：
let alert = TopAlertController()
alert.title = "title"
alert.message = "message"
alert.addAction(UIAlertAction(title: "Ок", style: .default, handler: { _ in }))
alert.show()
在调用类方法之前注册通知。
SWIFT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。