UIAlertController disappearing since iOS 13

问题

I have the following function that pops up a UIAlert which allows the user to update their Haptic Feedback setting:

- (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];
}

I have used this for a couple of years and it works great.

However, since updating to iOS 13 and updating to the latest Xcode, my alert pops up for less than a second before closing.

What has changed that could be making this happen? Thanks in advance.

回答1:

What seems to have changed is that on iOS 12 and previous versions your app would hold a strong reference to the window just by calling [alertWindow makeKeyAndVisible];, in iOS 13 it doesn't anymore.

What's happening is that the only strong reference to your alertWindow is in your requestHapticSetting func, and as soon as this func returns, the window is destroyed, thus removing your alert from the view.

This might be fixed just by adopting iOS 13 scenes, but I haven't tested that. What I can suggest, which won't properly work if you are using scenes, is holding your alert window in a strong variable somewhere in your code, and then using it to present the alert. I'd suggest doing so in a singleton or AppDelegate itself.

//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];
}

For Swift code, check this answer.

来源：https://stackoverflow.com/questions/58148334/uialertcontroller-disappearing-since-ios-13

标签

objective-c

uialertview

uialertcontroller

ios13