[objective-c] iOS application: how to clear notifications?

I've an iOS application where some Push Notification are sent to. My problem is, that the messages/notifications stays in the Notification Center in iOS after then are tapped. How can I remove a notification for my application in the Notification Center next time the application opens?

I came across posts where people are calling setApplicationIconBadgeNumber to a zero-value to clear the notifications. That's seems very weird to me, so I believe that maybe another solution exists?

EDIT1:

I'm having some problems clearing the notifications. Please see my code here:

- (void) clearNotifications {
    [[UIApplication sharedApplication] setApplicationIconBadgeNumber: 0];
    [[UIApplication sharedApplication] cancelAllLocalNotifications];
}

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    if (launchOptions != nil)
    {
        NSDictionary* dictionary = [launchOptions objectForKey:UIApplicationLaunchOptionsRemoteNotificationKey];
        if (dictionary != nil)
        {
            NSLog(@"Launched from push notification: %@", dictionary);

            [self clearNotifications];
        }
    }

    return YES;
}

- (void)application:(UIApplication*)application didReceiveRemoteNotification:(NSDictionary*)userInfo
{    
    NSLog(@"Received notification: %@", userInfo);
    [self clearNotifications];
}

I'm running the App through Xcode. When the App is minimized and I start the App using the notification in the Notification Center, I can see in the log, that the didReceiveRemoteNotification is called and using breakpoints I can see, that the clearNotifications has ran. But still the notification hangs in the Notification Center. Why?

If you have pending scheduled local notifications and don't want to use cancelAllLocalNotifications to clear old ones in Notification Center, you can also do the following:

[UIApplication sharedApplication].scheduledLocalNotifications = [UIApplication sharedApplication].scheduledLocalNotifications;

It appears that if you set the scheduledLocalNotifications it clears the old ones in Notification Center, and by setting it to itself, you retain the pending local notifications.

Update for iOS 10 (Swift 3)

In order to clear all local notifications in iOS 10 apps, you should use the following code:

import UserNotifications

...

if #available(iOS 10.0, *) {
    let center = UNUserNotificationCenter.current()
    center.removeAllPendingNotificationRequests() // To remove all pending notifications which are not delivered yet but scheduled.
    center.removeAllDeliveredNotifications() // To remove all delivered notifications
} else {
    UIApplication.shared.cancelAllLocalNotifications()
}

This code handles the clearing of local notifications for iOS 10.x and all preceding versions of iOS. You will need to import UserNotifications for the iOS 10.x code.

If you're coming here wondering the opposite (as I was), this post may be for you.

I couldn't figure out why my notifications were clearing when I cleared the badge...I manually increment the badge and then want to clear it when the user enters the app. That's no reason to clear out the notification center, though; they may still want to see or act on those notifications.

Negative 1 does the trick, luckily:

[UIApplication sharedApplication].applicationIconBadgeNumber = -1;

Just to expand on pcperini's answer. As he mentions you will need to add the following code to your application:didFinishLaunchingWithOptions: method;

[[UIApplication sharedApplication] setApplicationIconBadgeNumber: 0];
[[UIApplication sharedApplication] cancelAllLocalNotifications];

You Also need to increment then decrement the badge in your application:didReceiveRemoteNotification: method if you are trying to clear the message from the message centre so that when a user enters you app from pressing a notification the message centre will also clear, ie;

[[UIApplication sharedApplication] setApplicationIconBadgeNumber: 1];
[[UIApplication sharedApplication] setApplicationIconBadgeNumber: 0];
[[UIApplication sharedApplication] cancelAllLocalNotifications];

When you logout from your app, at that time you have to use a below line of code on your logout button click method.

[[UIApplication sharedApplication] setApplicationIconBadgeNumber: 0];

[[UIApplication sharedApplication] cancelAllLocalNotifications];

and this works perfectly in my app.

You need to add below code in your AppDelegate applicationDidBecomeActive method.

[[UIApplication sharedApplication] setApplicationIconBadgeNumber: 0];

When you have repeated notifications at future, you do not want to cancel those notifications, you can clear the item in notification center by:

func clearNotificationCenter() {
    UIApplication.sharedApplication().applicationIconBadgeNumber = 1
    UIApplication.sharedApplication().applicationIconBadgeNumber = 0
}

You cannot clear notification when your app is open in the foreground by calling the method below immediately after receiving local notification, otherwise you will receive tens of hundreds of notifications. Maybe because the same notification apply again, and now is the time to fire, so you keep fire, apply again, fire, apply....:

[UIApplication sharedApplication].scheduledLocalNotifications = [UIApplication sharedApplication].scheduledLocalNotifications;

It might also make sense to add a call to clearNotifications in applicationDidBecomeActive so that in case the application is in the background and comes back it will also clear the notifications.

- (void)applicationDidBecomeActive:(UIApplication *)application
{
    [self clearNotifications];
}

In Swift I'm using the following code inside my AppDelegate:

func applicationDidBecomeActive(application: UIApplication) {
    application.applicationIconBadgeNumber = 0
    application.cancelAllLocalNotifications()
}

Got it from here. It works for iOS 9

UIApplication *app = [UIApplication sharedApplication];
NSArray *eventArray = [app scheduledLocalNotifications];
for (int i=0; i<[eventArray count]; i++)
{
    UILocalNotification* oneEvent = [eventArray objectAtIndex:i];
    //Cancelling local notification
    [app cancelLocalNotification:oneEvent];
}

Maybe in case there are scheduled alarms and uncleared app icon badges.

NSArray *scheduledLocalNotifications = [application scheduledLocalNotifications];
NSInteger applicationIconBadgeNumber = [application applicationIconBadgeNumber];

[application cancelAllLocalNotifications];
[application setApplicationIconBadgeNumber:0];

for (UILocalNotification* scheduledLocalNotification in scheduledLocalNotifications) {
    [application scheduleLocalNotification:scheduledLocalNotification];
}
[application setApplicationIconBadgeNumber:applicationIconBadgeNumber];