How to access data passed in iOS notification (simple)?

Question

Trying to get one ViewController to communicate with another through standard Cocoa Notifications.

Wrote a simple test case. In my initial VC I add the following to viewDidLoad:

[[NSNotificationCenter defaultCenter] addObserver:self 
 selector: @selector(mesageReceived:)
 name:@"test.channel.pw" object:nil];

I add the following method:

- (void)mesageReceived:(NSNotification *)notif
{
    NSString *text = (NSString *)notif;    
}

I then segue to a VC which has the following added to its viewDidLoad:

  NSString *test = @"someText";
 [[NSNotificationCenter defaultCenter]
     postNotificationName:@"test.channel.pw" object:test];

When I run it, the notification works - the messageReceived method is called - but the value of text is "test.channel.pw", not "someText" as I expected.

What is going on here, and what is the correct syntax for passing a reference to a class instance using notifications?

possible duplicate of [How to pass object with NSNotificationCenter](http://stackoverflow.com/questions/7896646/how-to-pass-object-with-nsnotificationcenter) — Idrees Ashraf, Sep 04 '15 at 12:08

score 0 · Answer 1 · answered Sep 04 '15 at 12:10

You need to pass your data using userInfo dictionary.

Change the notification passing code like:

[[NSNotificationCenter defaultCenter] postNotificationName:@"test.channel.pw" object:nil userInfo:[NSDictionary dictionaryWithObject:@"someText" forKey:@"dataKey"]];

And change the receiver method like:

- (void)mesageReceived:(NSNotification *)notif
{
    NSString *text = [[notif userInfo] objectForKey:@"dataKey"];    
}

score 0 · Answer 2 · answered Sep 04 '15 at 12:11

0

Try NSString *text = (NSString *)[notif object];.

answered Sep 04 '15 at 12:11

Phillip Mills

30,888
4
42
57

score 0 · Answer 3 · answered Sep 04 '15 at 12:15

By this

-(void)someMethod{
  NSDictionary *postDict = @{@"Key":[NSNumber numberWithFloat:17.0]};
[[NSNotificationCenter defaultCenter]postNotificationName:@"myNotification" object:postDict];
}

Some other class

-(void)viewDidLoad{
[[NSNotificationCenter defaultCenter]postNotificationName:@"myNotification" object:nil userInfo:postDict];
}
-(void)valueForNotification:(NSNotification *)notification{
NSDictionary *dict = [notification userInfo];
NSLog(@"%@",[dict objectForKey:@"Key"]); //prints out 17.0
}

score 0 · Answer 4 · answered Sep 04 '15 at 12:16

0

You need to pass only NSDictionary object in NSnotificationCenter. Through NSDictionary you can pass any data and then you need to parse once received.

answered Sep 04 '15 at 12:16

Idrees Ashraf

1,363
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How to access data passed in iOS notification (simple)?

4 Answers4