Send NSNotification from classA to classB

Question

So i have an app with an In App purchase. The In App purchase is managed in FirstViewController. When the user has purchased the product, i want to send out a Notification to my MainTableViewController to reload the tables data and show the new objects that were purchased in the In App purchase. So basically i want to send a notification from class A to class B and class B reloads the data of the tableview then. I have tried using NSNotificationCenter, but with no success, but i know that its possible with NSNotificationCenter i just don't know how.

Lawn

Answer 1

In class A : post the notification

[[NSNotificationCenter defaultCenter] postNotificationName:@"DataUpdated"
                                                        object:self];

In class B : register first for the notification, and write a method to handle it.
You give the corresponding selector to the method.

// view did load
[[NSNotificationCenter defaultCenter] addObserver:self
                                         selector:@selector(handleUpdatedData:)
                                             name:@"DataUpdated"
                                           object:nil];

-(void)handleUpdatedData:(NSNotification *)notification {
    NSLog(@"recieved");
    [self.tableView reloadData];
}

Fist

it should. you don't need more to run notifications. if classA updates some data, make sure these changes are reflected in classB. you can also use notifications to give classB a value, but reloadData will make the tableView asking its datasource for the data again. – Fist

well, the -(void)updated {[self.tableView reload data];} does not get called when the notification is sent, please check your code, ive tried modifying the code but it didn't help. – Lawn

@Maxner - the problem is surely elsewhere check out Apple's Notification Programming Topics, you will see notifications system is easy as I wrote. – Fist

ok, still thank you for the code, i will upvote both yours and Rahul Vyas answer. – Lawn

@Maxner - please make sure using this code you are effectively registering for the notification at some point. you could easily check it by logging some message just before. did you put the registration method call in viewDidLoad in MainTableViewController ? – Fist

@Maxner - so 2 last points to check : 1) do the two classes post and register for the same notification names ("DataUpdated" in the example) ? 2) does the selector (@selector(handleUpdatedData:)) correspond to the method name (-(void)handleUpdatedData:(NSNotification *)notification;) ? – Fist

yes everything is spelled correctly, ive also made it easier, by calling the selector "b:" and the notification name "a", problem is still there... – Lawn

@Maxner - really, really interesting, is the notification really posted ? did you put a NSLog call just before posting it ? – Fist

yes it is being posted, i first put it into SKPaymentTransactionStatePurchased: it got called for sure there along with an NSLog and UIAlertView, now i have just connected the notification to an ibaction of a button to make testing faster, its getting called too and nothing is happening. i dont understand it... – Lawn

If it helps: ClassA is a UIViewController, classB is a UITableViewController. the view of ClassB is a subview of classA's view. – Lawn

@Maxner - yes a bit, try to register for the notification in your UITableViewController subclass initializer. – Fist

do you mean the - (id)initWithStyle:(UITableViewStyle)style method? Doesn't work either. – Lawn

@Maxner - but what isn't working ? are the method calls reached at some point, did you verify it ? look at the link in my answer, it should work like that. – Fist

The method name is misspelled: The correct methodname should not be: postNotficationName but: postNotificationName (with an extra i). Maybe this solves the problem? (I cannot edit the post as edits should be more than 6 characters..) – Eudocia

not sure of best method, but in other stackoverflow code, i've seen in class B, register for notification in viewWillAppear and remove observer in viewWillDisappear. – Totipalmate

Don't forget to remove the notification observer in viewWillDisappear. – Polis

Answer 2

Ok I'm adding a little bit more information to vince's answer

In class A : post the notification

[[NSNotificationCenter defaultCenter] postNotificationName:@"DataUpdated"
                                                   object:arrayOfPurchasedObjects];

In class B : register first for the notification, and write a method to handle it.
You give the corresponding selector to the method. Make sure your class B is allocated before you post the notification otherwie notification will not work.

- (void) viewDidLoad {
// view did load
[[NSNotificationCenter defaultCenter] addObserver:self
                                         selector:@selector(handleUpdatedData:)
                                             name:@"DataUpdated"
                                           object:nil];
}

-(void)handleUpdatedData:(NSNotification *)notification {
    NSLog(@"recieved");
    NSArray *purchased = [notification object];
    [classBTableDataSourceArray addObjectsFromArray:purchased];
    [self.tableView reloadData];
}

- (void) dealloc {
    // view did load
    [[NSNotificationCenter defaultCenter] removeObserver:self
                                                 name:@"DataUpdated"
                                               object:nil];
    [super dealloc];
 }

Rolfrolfe

thx but its not working either, also i use NSUserdefaults to recognize if the in app purchase is complete, so i dont need to add objects to the array. – Lawn

for new folks (me), there is a typo in answer above, 'postNotficationName' throws an error, 'postNotificationName' (with another 'i') corrects it. (thank you Rahul Vyas for helping to clarify notifications process). – Totipalmate

There is a typo in your answer @RahulVyas , it is not "postNotficationName" it is "postNotificationName" – Polis

Answer 3

Maybe you trying to send notification from another thread? NSNotification won't be delivered to the observer from another thread.

Casseycassi

Try to compare [NSThread currentThread] in place where you generate notification to [NSThread mainThread] in class which observe for notification. – Casseycassi

Also make sure, what you not specified object when adding observer. – Casseycassi