UIAlertController自iOS 13起消失

Question

我具有以下功能，该功能会弹出UIAlert，允许用户更新其触觉反馈设置：

- (void)requestHapticSetting{
    UIWindow *alertWindow = [[UIWindow alloc] initWithFrame:[UIScreen mainScreen].bounds];
    alertWindow.rootViewController = [[UIViewController alloc] init];
    alertWindow.windowLevel = UIWindowLevelAlert + 1;
    [alertWindow makeKeyAndVisible];

    if(isHapticOn){
        hapticMessage = @"Haptic feedback is currently\nturned ON.\nPlease update preference.";
    }
    else {
        hapticMessage = @"Haptic feedback is currently\nturned OFF.\nPlease update preference.";
    }

    UIAlertController* alert = [UIAlertController alertControllerWithTitle:@"Haptic Setting"
                                                                   message:hapticMessage
                                                            preferredStyle:UIAlertControllerStyleAlert];

    UIAlertAction* onAction = [UIAlertAction actionWithTitle:@"TURN ON" style:UIAlertActionStyleDefault
                                                     handler:^(UIAlertAction * action) {
                                                         [self saveHapticSettingOn];
                                                     }];

    UIAlertAction* offAction = [UIAlertAction actionWithTitle:@"TURN OFF" style:UIAlertActionStyleDefault
                                                      handler:^(UIAlertAction * action) {
                                                          [self saveHapticSettingOff];
                                                      }];
    [alert addAction:offAction];
    [alert addAction:onAction];
    [alertWindow.rootViewController presentViewController:alert animated:YES completion:nil];
}

我已经使用了几年，效果很好。

但是，由于更新到iOS 13并更新到最新的Xcode，我的警报在关闭前弹出不到一秒钟。

发生了什么变化才能使这种情况发生？预先感谢。

Answer 1

[似乎已经改变的是，在iOS 12和更低版本上，您的应用仅通过调用[alertWindow makeKeyAndVisible];即可拥有对窗口的强烈引用，而在iOS 13中不再可用。

正在发生的事情是，对alertWindow的唯一强大引用是在requestHapticSetting函数中，并且一旦该函数返回，窗口就会被破坏，从而从视图中删除警报。

这可能仅通过采用iOS 13场景即可解决，但我尚未对此进行测试。我所建议的，

如果使用场景将无法正常工作，是将警报窗口保存在代码中某个位置的强变量中，然后使用它来呈现警报。我建议在单例或AppDelegate本身中这样做。

//AppDelegate.h
...
@property (strong) UIWindow *alertWindow;
....

//AppDelegate.m
...
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    ...
    self.alertWindow = [[UIWindow alloc] init];
    self.alertWindow.rootViewController = [[UIViewController alloc] init];
    self.alertWindow.windowLevel = UIWindowLevelAlert + 1;
    ...
}
...

//Your class that's presenting the alert
#import "AppDelegate.h"
...
- (void)requestHapticSetting{
    AppDelegate *appDelegate = (AppDelegate *)UIApplication.sharedApplication;
    [alertWindow makeKeyAndVisible];
    if(isHapticOn){
        hapticMessage = @"Haptic feedback is currently\nturned ON.\nPlease update preference.";
    } else {
        hapticMessage = @"Haptic feedback is currently\nturned OFF.\nPlease update preference.";
    }

    UIAlertController* alert = [UIAlertController alertControllerWithTitle:@"Haptic Setting"
                                                               message:hapticMessage
                                                        preferredStyle:UIAlertControllerStyleAlert];

    UIAlertAction* onAction = [UIAlertAction actionWithTitle:@"TURN ON" style:UIAlertActionStyleDefault
                                                 handler:^(UIAlertAction * action) {
                                                      [self saveHapticSettingOn];
                                                      [((AppDelegate *)UIApplication.sharedApplication).alertWindow setHidden:YES];
                                                 }];

    UIAlertAction* offAction = [UIAlertAction actionWithTitle:@"TURN OFF" style:UIAlertActionStyleDefault
                                                  handler:^(UIAlertAction * action) {
                                                      [self saveHapticSettingOff];
                                                      [((AppDelegate *)UIApplication.sharedApplication).alertWindow setHidden:YES];
                                                  }];
    [alert addAction:offAction];
    [alert addAction:onAction];
    [alertWindow.rootViewController presentViewController:alert animated:YES completion:nil];
}

对于Swift代码，请检查this answer。