UIAlertController 自 iOS 13 起消失

Question

我有以下功能会弹出一个 UIAlert，允许用户更新他们的触觉反馈设置：

- (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];
}

我已经用了几年了，效果很好。

但是，自从更新到 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。

发生了什么变化可能会导致这种情况发生？提前致谢。

Answer 1

似乎发生了变化的是，在 iOS 12 和以前的版本中，您的应用程序只需调用 即可持有对窗口的强引用[alertWindow makeKeyAndVisible];，而在 iOS 13 中则不再如此。

发生的事情是对您的唯一强引用alertWindow在您的requestHapticSettingfunc 中，并且一旦此 func 返回，窗口就会被销毁，从而从视图中删除您的警报。

这可能仅通过采用 iOS 13 场景就可以解决，但我尚未对此进行测试。我可以建议，如果您使用场景将无法正常工作，将您的警报窗口放在代码中某处的强变量中，然后使用它来显示警报。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;
    [appDelegate.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.alertWindow setHidden:YES];
                                                 }];

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

对于 Swift 代码，请查看此答案。