i am new Notification.what is the purpose of it...
can we use [[NSNotificationCenter defaultCenter] addObserver without postNotification,
If we can do it,how it is identified?what is the relationship between addObserver and postNotification?any one can explain in detail?
it's rather straight forward: you define an event by giving it a unique name, then you add an observer to it using [[NSNotificationCenter defaultCenter] addObserver and point it to a selector that receives the event.
then later on in your code you can postNotification and if the unique name matches the one you registered for - the selector you provided will be called.
Related
[[NSNotificationCenter defaultCenter] postNotificationName:kNotificationForbidAdvPost object:nil];
I define postNotificationName:kNotificationForbidAdvPost in a .h file
Im my subclass of NSApplication, I import this .h file. And have a observer of this Notification
[[NSNotificationCenter defaultCenter] addObserver:self selector:#selector(changeToRecordingStatus) name:kNotificationForbidAdvPost object:nil];
I am sure that the observer was added first, and then post the notification.
And I see the [UINotification default] in Debug. It have same memory address in two part of code.
Is there some mistake I have?
Thanks!
The documentation is pretty clear when it states that
The method specified by
notificationSelector must have one and
only one argument (an instance of
NSNotification).
http://developer.apple.com/library/mac/documentation/Cocoa/Reference/Foundation/Classes/NSNotificationCenter_Class/Reference/Reference.html#//apple_ref/doc/uid/20000219-CHDCIGGB
So, I see your selector you are registering is changeToRecordingStatus when it must be changeToRecordingStatus:
- (void) changeToRecordingStatus: (NSNotification *) notification;
I have try that add a arugument, but it is still not worked.
I create a new project and use a no-argument function to response Notification, it is worked normally.
The reason why I cannot receive the Notification is that a removeObserver method was called at one part which I didn't notice.
Thanks for all your reply.
I have a parser class and a view controller class. In the parser class i am sending a request and receiving an asynchronous response. I want to download the same several times but while sending different parameters each time. I have registered an observer in the class:
[[NSNotificationCenter defaultCenter] addObserver:self selector:#selector(dataDownloadComplete:) name:OP_DataComplete object:nil];
and then post a notification in :
-(void)connectionDidFinishLoading:(NSURLConnection *)
connection method of the parser class.
[[NSNotificationCenter defaultCenter] postNotificationName:OP_DataComplete object:nil];
I can't enclose the observer inside a For loop. What better alternative is there? Please help. Thanks in advance.
You probably do not need a for loop at all. As you said you send a request asynchroniously, so just send it in your observer code instead of making a for loop. Then you get back to your observer after response is downloaded.
I set up a notification observer in my view controller's init method like so:
[[NSNotificationCenter defaultCenter]
addObserver:self
selector:#selector(saveState)
name:UIApplicationWillResignActiveNotification
object:nil];
Where is the best place to call removeObserver:name:object: for this notification. I'm currently calling it in my dealloc method, but wanted to know if that might cause problems.
No, you got it right. dealloc is the correct location to remove notification observers (unless you have some specific reason to need to remove the observer earlier).
You can always remove the observer in viewWillDisappear:, or when you are done using it and have no other need for it, you can place it in a function.
If the -saveState only need to execute once when active, then you can removeObserver inside the -saveState.
i have 2 classes.
class1 gets some information through the net. when one of these informations comes, class1 has to send a notification to class2.
i understood it so that i have to put
[[NSNotificationCenter defaultCenter] postNotificationName:at"anyUserNotification" object:class2];
into class1
[[NSNotificationCenter defaultCenter] addObserver:self selector:atselector(anyInteraction:) name:dontKnowTheSense object:dunno2];
have i understood the object:class2 in the postnotification right ?
if yes: is it possible to make an anonymious notification, so that the sending class must not know, which and how many classes are listening ?
or - at least i think so, have i understood the whole notification incorrect ?
besides the notification i dont need to pass any data, but in one case it would be helpful to pass an enum
so, could anybody please help me ?
btw: i cant find a way to post an at on this windows-pc and i dont know, why it did not indent the code, i think i made 4 spaces
Object is not a mandatory argument you can set it to nil or the object sending the notification message.
[[NSNotificationCenter defaultCenter] postNotificationName:#"NotificationName" object:notificationSenderOrNil];
When listening you can filter to only do something for notification sent by a specific sender.
[[NSNotificationCenter defaultCenter] addObserver:self selector:#selector(sel) name:#"NotificationName" object:notificationSenderOrNil];
And you can pass your data in a dictionnary with userInfo: argument.
Is it Ok with that ?
Is it OK to use -removeObserver: first and then call -addObserver: with the same name? Or is it a rule to have -addObserver: first before -removeObserver:?
I tried it using OS 4.0 and it seems OK (no crash, warnings... etc.).
-(void) setObserver
{
[[NSNotificationCenter defaultCenter] removeObserver:self
name:OBSERVER_NAME object:nil];
[[NSNotificationCenter defaultCenter] addObserver:self
selector: #selector(selectorName)
name:OBSERVER_NAME
object:nil];
}
The reason is to prevent two observers with the same selectorName method being called twice assuming that -setObserver method was called again if its inside -viewDidLoad and a memory warning was issued.
Also, do I need to invoke -removeObserver: during -dealloc?
If you're getting -selectorName invoked twice, there's probably some other issue with your code. And even if Cocoa will be graceful about removing observers you haven't added yet, I wouldn't actually do that.
As user tonklon says in a comment, you should probably remove the observer in -viewDidUnload. As to your last question, it's also reasonable to remove the observer in -dealloc, though it's good practice to structure your code such that things like removing observers happen at a deterministic time rather than as a side-effect of memory management.