Quickies for Notifications

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Blocks

• Register a notification with a block [permalink]
  

          [center addObserverForName: kGRZoneSystem_ZoneSystemChangedNotification
                  object: nil
                  queue: [NSOperationQueue mainQueue]
                  usingBlock: ^(NSNotification *notification) {
                  [self adaptToZoneChange];
              }];
  

General

• Posting notifications. [permalink]
  In the header file:

  extern NSString *BWStitchGroup_VisualAttributeChangeNotification;

  In the .m file:

  NSString *BWStitchGroup_VisualAttributeChangeNotification
    = @"BWStitchGroup Visual Attribute Change Notification";
...
  

  NSNotificationCenter *center;
  center = [NSNotificationCenter defaultCenter];
  
  [center postNotificationName: 
              BWStitchGroup_VisualAttributeChangeNotification
          object: self];

  If you want to pass a userinfo dictionary, you can use a variant method:

      NSDictionary *userInfo = ...;
      [center postNotificationName: BWStitchGroup_VisualAttributeChangeNotification
              object: self
              userInfo: userInfo];
  

• Receiving notifications [permalink]
  

  NSNotificationCenter *center;
  center = [NSNotificationCenter defaultCenter];
  
  [center addObserver: self
          selector: @selector(groupVisualChange:)
          name: BWStitchGroup_VisualAttributeChangeNotification
          object: group];
  

  Where the selector looks like this:

  - (void) groupVisualChange: (NSNotification *) notification
  {
      // do stuff with the notification
  } // groupVisualChange

• Removing yourself from notifications [permalink]
  Don't forget to unregister yourself from the notification center in your -dealloc:

      NSNotificationCenter *center = [NSNotificationCenter defaultCenter];
      [center removeObserver: self];
  

• Watching all notifications [permalink]
  There's three notification centers - one for the app, one for the workspace, and the distributed notification center. Here's how to watch everything:

  #import <Cocoa/Cocoa.h>
  #import <stdio.h> // for printf()
  
  @interface NotificationSpy
  {
  }
  
  + (void) startSpying;
  + (void) stopSpying;
  
  @end // NotificationSpy
  
  
  // prevent us from adding ourselves multiple times
  
  static BOOL g_spying;
  
  
  @implementation NotificationSpy
  
  // turn on listening for all notifications.
  
  + (void) startSpying
  {
      if (!g_spying) {
          NSNotificationCenter *center;
  
          // first the default notification center, which is all
          // notifications that just happen inside of our program
  
          center = [NSNotificationCenter defaultCenter];
          
          [center addObserver: self
                  selector: @selector(observeDefaultCenterStuff:)
                  name: nil
                  object: nil];
  
          // then the NSWorkspace notification center, which tells us things
          // like other applications launching, and the machine sleeping
          // and waking
  
          center = [[NSWorkspace sharedWorkspace]
                       notificationCenter]; 
  
          [center addObserver: self
                  selector: @selector(observeWorkspaceStuff:)
                  name: nil
                  object: nil];
  
          // and lastly the distributed notification center.  This is a
          // global (to the computer) notification center.  You can find
          // out when a different program gets focus, or the sound or
          // screen brightness changes.
  
          center = [NSDistributedNotificationCenter 
                       notificationCenterForType: NSLocalNotificationCenterType];
  
          [center addObserver: self
                  selector: @selector(observeDistributedStuff:)
                  name: nil
                  object: nil];
  
          g_spying = YES;
      }
  
  } // startSpying 
  
  
  // remove us as observers
  
  + (void) stopSpying
  {
      if (!g_spying) {
          NSNotificationCenter *center;
  
          // take us off the default center for our app
          center = [NSNotificationCenter defaultCenter];
          [center removeObserver: self];
  
          // and for the workspace
          center = [[NSWorkspace sharedWorkspace] 
                       notificationCenter];
          [center removeObserver: self];
  
          // and finally off of the machine-wide center
          center = [NSDistributedNotificationCenter 
                       notificationCenterForType: NSLocalNotificationCenterType];
          [center removeObserver: self];
  
          g_spying = NO;
      }
  
  } // stopSpying
  
  
  
  + (void) observeDefaultCenterStuff: (NSNotification *) notification
  {
      // QuietLog can also be found in the quickies
      QuietLog (@"default: %@", [notification name]);
  } // observeDefaultCenterStuff
  
  
  
  + (void) observeDistributedStuff: (NSNotification *) notification
  {
      QuietLog (@"distributed: %@", [notification name]);
  } // observeDistributedStuff
  
  
  
  + (void) observeWorkspaceStuff: (NSNotification *) notification
  {
      QuietLog (@"workspace: %@", [notification name]);
  } // observeWorkspaceStuff
  
  
  @end // NotificationSpy

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