NSNotifications name best practice

Question

In trying to de-couple my model from the view controllers that display fetched data, when an asynchronous fetch completes, I post an NSNotification.

 [[NSNotificationCenter defaultCenter] postNotificationName:@"foobarFetchSuccess" object: foo];

I've gotten into the habit of using:

 #define FOO_FETCH_SUCCESS  @"foobarFetchSuccess"

in a common header file and then using it for the addObserver: and removeObserver: as well as the postNotificationName:

 [[NSNotificationCenter defaultCenter] addObserver:self @selector(gotData)
                                              name:FOO_FETCH_SUCCESS object: baz];

So @"foobarFetchSuccess" string is used all over the place. And there are many more just like him. So what's the best way to declare a string once and use it everywhere?

Heavyset

Answer 1

As for using constant strings in your project, there’s another question on Stack Overflow about that: Constants in Objective C.

As for naming notifications, Coding Guidelines for Cocoa suggests the following:

Notifications are identified by global NSString objects whose names are composed in this way:

[Name of associated class] + [Did | Will] + [UniquePartOfName] + Notification

Mediatorial

For the sake of completion, what about the naming convention for the observing selector? According to the guideline, it's almost the same as the Notification name, minus "Notification" and the class namespace prefix. eq: windowDidLoad Is this accurate? – Besprent

@pix You can name them at your will. However, if it’s a delegate method that is called because of a notification, then what you’ve said applies — a delegate wouldn’t register for the notification; instead, it’d automatically receive the corresponding message with the notification parameter. Note that -windowDidLoad is not really related to a notification (it doesn’t receive an NSNotification argument), but the naming convention is similar indeed. – Mediatorial

My gripe with the convention is that names become really long and overall readability is negatively impacted. – Clinch

Answer 2

This doesn't follow the Apple-suggested format exactly, nor does it directly answer your question, but I thought I'd share these handy-dandy text macros that I use to spare myself a little typing when making notification and key names. You can assign these a keyboard shortcut, type in and select the [Did|Will] + [UniquePartOfName] segment, then hit the shortcut to produce the variable and its value. You could also use $(FILENAMEASIDENTIFIER) instead of $(PROJECTNAME) if you were defining these strings in the header of a particular class, and that would conform to the suggestion.

//MARK: Notification strings
    { /*
       * Use the selection to make the name and string for a Notification.
       * The string has a prefix placeholder, defaulting to the project name.
       */
      Identifier = objc.notestring;
      BasedOn = objc;
      IsMenuItem = YES;
      Name = "Notification Name From Selection";
      TextString = "<#$(PROJECTNAME)#><#!notename!#>Notification = @\"<#$(PROJECTNAME)#><#!notename!#>Notification\";";
      CompletionPrefix = notestring;
    },
    { /*
       * Insert placeholders to make the name and string for a Notification.
       * This is for use without a selection, and so "only" activates at the 
       * beginning of the line.
       */
      Identifier = objc.notestring.bol;
      BasedOn = objc.notestring;
      IsMenuItem = YES;
      Name = "Notification Name From Selection";
      OnlyAtBOL = YES;
      CompletionPrefix = notestring;
    },

//MARK: Default Key strings
    { /*
       * Convert the selection into a name and string for use in the User 
       * Defaults system. The string has a placeholder for a prefix, which
       * defaults to the project name.
       */
      Identifier = objc.defaultskeystring;
      BasedOn = objc;
      IsMenuItem = YES;
      Name = "UserDefaults Key From Selection";
      OnlyAtBOL = NO;
      TextString = "<#$(PROJECTNAME)#><#!keyname!#>Key = @\"<#$(PROJECTNAME)#><#!keyname!#>Key\";";
      CompletionPrefix = defaultskey;
    },
    { /*
       * Insert placeholders to make the name and string for a a key for the
       * User Defaults system. This is for use without a selection, and so 
       * "only" activates at the beginning of the line.
       */
      Identifier = objc.defaultskeystring.bol;
      BasedOn = objc.defaultskeystring;
      IsMenuItem = YES;
      OnlyAtBOL = YES;
      Name = "UserDefaults Key From Selection";
      CompletionPrefix = defaultskey;
    },

These are Xcode 3 macros. I know the macro system is different in Xcode 4 (which I'm not using yet), but I believe the conversion is simple and can be automated.

Flavour