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
iOS13场景支持(当使用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
}
}
}
其他回答
交叉张贴我的答案，因为这两个线程没有被标记为欺骗…
现在UIViewController是responder chain的一部分，你可以这样做:
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)
}
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)
}
}
}
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];
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。
在Objective-C中显示警报的简单方法:
[[[[UIApplication sharedApplication] keyWindow] rootViewController] presentViewController:alertController animated:YES completion:nil];
alertController是你的UIAlertController对象。
注意:你还需要确保你的助手类扩展了UIViewController
