How to handle multiple alerts firing at the same time

Question

I have multiple nsnotificationcenters running at one time that display an alert when triggered. At times, this causes more than one alert to fire at a time but of course you can only display one and the other does not appear. What is the best way handle this situation so multiple alerts can go in succession.

I have tired having the alerts in one method and when one alert is showing, put another notification in an array and then run through that array but that is not working correctly. I have also tried to have the alerts in separate methods but that is not working either.

I have looked at using semaphores but could not find a good example.

This is my notifications which works as expected. I was looking for some advice on the notifications also. Where would be the best place to add the observer, in the viewDidAppear of viewDidLoad. viewDidLoad give a warning whenever an alert is displayed because it wants to display on a view that is not in the hierarchy.

- (void)viewDidAppear:(BOOL)animated {
    [super viewDidAppear:animated];
    // * 26 APR 2019 * 1.0.4.0
    // Add observer for notifications
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(receivedNotification:) name:@"ROC" object:nil];
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(receivedNotification:) name:@"ROP" object:nil];
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(receivedNotification:) name:@"CARGO" object:nil];
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(receivedNotification:) name:@"PAX" object:nil];

}

This is my selector method using a single method for all of the alerts. I am new to coding so I am sure this is not good practice so any advice would be appreciated. I am trying to put any additional notifications in an array if the current view is a uialertcontroller and then run through the array and display those alerts after but that is not working how i would like it to.

- (void)viewDidAppear:(BOOL)animated {
    [super viewDidAppear:animated];
    // * 26 APR 2019 * 1.0.4.0
    // Add observer for notifications
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(receivedNotification:) name:@"ROC" object:nil];
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(receivedNotification:) name:@"ROP" object:nil];
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(receivedNotification:) name:@"CARGO" object:nil];
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(receivedNotification:) name:@"PAX" object:nil];

}

- (void)receivedNotification:(NSNotification *)notification {
    NSMutableDictionary *msgData = [[FlightDataInput sharedFlightDataInput] dataForPage:4];
    NSMutableArray *alertArray = [[NSMutableArray alloc] init];

    if([self.presentedViewController isKindOfClass:[UIAlertController class]]) {
        [alertArray addObject:notification];
    }

    if(![self.presentedViewController isKindOfClass:[UIAlertController class]] && [alertArray count] == 0) {

        if([notification.name  isEqualToString: @"ROC"]) {

            UIAlertController *alertRoc = [UIAlertController alertControllerWithTitle:[msgData valueForKey:@"rocTitle"] message:[msgData valueForKey:@"rocMsg"] preferredStyle:UIAlertControllerStyleAlert];
            UIAlertAction *ok = [UIAlertAction actionWithTitle:@"OK" style:UIAlertActionStyleDefault handler:^(UIAlertAction *action){
                [alertRoc dismissViewControllerAnimated:YES completion:nil];
            }];

            [alertRoc addAction:ok];

            [self presentViewController:alertRoc animated:NO completion:nil];
        }
        if ([notification.name isEqualToString:@"ROP"]) {
            UIAlertController *alertRop = [UIAlertController alertControllerWithTitle:[msgData valueForKey:@"ropTitle"] message:[msgData valueForKey:@"ropMsg"] preferredStyle:UIAlertControllerStyleAlert];
            UIAlertAction *ok = [UIAlertAction actionWithTitle:@"OK" style:UIAlertActionStyleDefault handler:^(UIAlertAction *action){
                [alertRop dismissViewControllerAnimated:YES completion:nil];
            }];

            [alertRop addAction:ok];

            [self presentViewController:alertRop animated:NO completion:nil];
        }
        if ([notification.name isEqualToString:@"CARGO"]) {
            UIAlertController *alertCargo = [UIAlertController alertControllerWithTitle:[msgData valueForKey:@"cargoTitle"] message:[msgData valueForKey:@"cargoMsg"] preferredStyle:UIAlertControllerStyleAlert];
            UIAlertAction *ok = [UIAlertAction actionWithTitle:@"OK" style:UIAlertActionStyleDefault handler:^(UIAlertAction *action){
                [alertCargo dismissViewControllerAnimated:YES completion:nil];
            }];

            [alertCargo addAction:ok];

            [self presentViewController:alertCargo animated:NO completion:nil];
        }
        if ([notification.name isEqualToString:@"PAX"]) {
            UIAlertController *alertPax = [UIAlertController alertControllerWithTitle:[msgData valueForKey:@"paxTitle"] message:[msgData valueForKey:@"paxMsg"] preferredStyle:UIAlertControllerStyleAlert];
            UIAlertAction *ok = [UIAlertAction actionWithTitle:@"OK" style:UIAlertActionStyleDefault handler:^(UIAlertAction *action){
                [alertPax dismissViewControllerAnimated:YES completion:nil];
            }];

            [alertPax addAction:ok];

            [self presentViewController:alertPax animated:NO completion:nil];
        }
    }
    if([alertArray count] > 0) {
        for(int i = 0; i < [alertArray count]; i++) {
            // creating the same alerts in here if there are alerts in the array
        }
    }
}

I have multiple nsnotificationcenters running at one time that display an alert when triggered. At times, this causes more than one alert to fire at a time but of course you can only display one and the other does not appear. What is the best way handle this situation so multiple alerts can go in succession.

I have tired having the alerts in one method and when one alert is showing, put another notification in an array and then run through that array but that is not working correctly. I have also tried to have the alerts in separate methods but that is not working either.

Do you want only last alert OR want to merge the text OR want to show multiple alerts? — TheTiger, May 17 '19 at 07:42
TheTiger, I would like to show multiple alerts. When you close the first alert the second will show if there is a second, or third. — D. Rock, May 22 '19 at 18:38
You can either go with Niraj's solution or you can make a custom alert with the help of `UIView` control. Then you can show it on window multiple times. — TheTiger, May 23 '19 at 08:29
I actually got it working using bits and pieces from other examples. — D. Rock, May 23 '19 at 20:18

score 2 · Answer 1 · answered May 17 '19 at 07:25

Hi you can present only one Alert at a time. if you want more in chain so first dismiss exist Alerts. Here is Sample please check and update.

{
  NSMutableDictionary *msgData;
  NSMutableArray <NSNotification *> *alertArray;
  int alertIndex;
}

- (void)viewDidLoad:(BOOL)animated {
    [super viewDidLoad:animated];
    // * 26 APR 2019 * 1.0.4.0
    // Add observer for notifications

    msgData = [[FlightDataInput sharedFlightDataInput] dataForPage:4];
    alertArray = [NSMutableArray new];
    alertIndex = 0;

    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(receivedNotification:) name:@"ROC" object:nil];
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(receivedNotification:) name:@"ROP" object:nil];
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(receivedNotification:) name:@"CARGO" object:nil];
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(receivedNotification:) name:@"PAX" object:nil];
}

- (void)receivedNotification:(NSNotification *)notification {

      [alertArray addObject:notification];
        if(![self isAlertExist]) {
          [self checkAlerts];           
         }
}


-(void) checkAlerts
{
  if(alertIndex < [alertArray count])
  {
    NSNotification *notification = (NSNotification *)[alertArray objectAtIndex:arrayIndex];
    arrayIndex = arrayIndex + 1;

    if([notification.name  isEqualToString: @"ROC"]) {
                [self showAlertWithTitle:[msgData valueForKey:@"rocTitle"] andMessage:[msgData valueForKey:@"rocMsg"]];
        }
        else if ([notification.name isEqualToString:@"ROP"]) {
          [self showAlertWithTitle:[msgData valueForKey:@"ropTitle"] andMessage:[msgData valueForKey:@"ropMsg"]];
        }
      else if ([notification.name isEqualToString:@"CARGO"]) {
          [self showAlertWithTitle:[msgData valueForKey:@"cargoTitle"] andMessage:[msgData valueForKey:@"cargoMsg"]];
        }
        else if ([notification.name isEqualToString:@"PAX"]) {
            [self showAlertWithTitle:[msgData valueForKey:@"paxTitle"] andMessage:[msgData valueForKey:@"paxMsg"]];
        }
  }
}

-(void) showAlertWithTitle:(NSString *)title andMessage:(NSString *)message
{
  UIAlertController *alertPax = [UIAlertController alertControllerWithTitle:title message:message preferredStyle:UIAlertControllerStyleAlert];
  UIAlertAction *ok = [UIAlertAction actionWithTitle:@"OK" style:UIAlertActionStyleDefault handler:^(UIAlertAction *action){
      [alertPax dismissViewControllerAnimated:YES completion:^{
        [self checkAlerts];
      }];
  }];

  [alertPax addAction:ok];
  [self presentViewController:alertPax animated:NO completion:nil];
}

-(BOOL) isAlertExist {
  for (UIWindow* window in [UIApplication sharedApplication].windows) {
     if ([window.rootViewController.presentedViewController isKindOfClass:[UIAlertController class]]) {
         return YES;
     }
 }
 return NO;
}

I tried this but it did not fix my issue. If there are multiple alerts, it still will only show the first one. Couple changes, in the checkAlert method, arrayIndex should be alertIndex. In isAlertExist method, it never returns yes. — D. Rock, May 17 '19 at 20:54
Instead of adding alerts on self view. Find top view and add on it. https://stackoverflow.com/questions/6131205/how-to-find-topmost-view-controller-on-ios — pallavi, Jun 19 '23 at 08:27

How to handle multiple alerts firing at the same time

1 Answers1