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
除了给出的很好的答案(agilityvision, adib, malhal)。为了达到像以前的UIAlertViews那样的排队行为(避免警报窗口重叠)，使用这个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
完整的例子:
[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。同样的方法可以用于为任意数量的窗口层分离和放入队列视图控制器。
其他回答
对于UINavigationController和/或UITabBarController的所有情况，非常通用的UIAlertController扩展。如果屏幕上有一个模态VC，也可以工作。
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)
}
}
}
}
你可以尝试在UIViewController上用一个方法来实现一个类别 - (void)presentErrorMessage;，在这个方法中你实现了UIAlertController，然后在self上呈现它。然后在你的客户端代码中，你会有这样的东西:
[myViewController presentErrorMessage];
这样可以避免不必要的参数和关于视图不在窗口层次结构中的警告。
创建扩展像在Aviel Gross回答。这里有Objective-C扩展。
这里有头文件*.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
和实现:*.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
你在你的实现文件中使用这个扩展，就像这样:
#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];
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.
}
其中一些答案只对我起了部分作用，将它们组合在AppDelegate中的以下类方法中是我的解决方案。它在iPad上工作，在UITabBarController视图中，在UINavigationController中，在呈现情态时。在iOS 10和13上进行测试。
+ (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 ...
