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Re: Notifications vs. messaging
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Re: Notifications vs. messaging


  • Subject: Re: Notifications vs. messaging
  • From: Nat! <email@hidden>
  • Date: Tue, 2 Oct 2001 00:41:47 +0200

Am Montag den, 1. Oktober 2001, um 13:01, schrieb Markus Hitter:

Am Montag, 1. Oktober 2001 um 00:41 schrieb Brian Hook:

Is there a simple guideline as to when to use a notification vs. when to send a message directly?

sending a method directly:

- much less overhead

- only one object per call

- is executed immediately

- you can get a return value


sending a notification:

- some overhead for queueing

- can be received by several subscribers

- is queued and sent from within the run loop. This makes a difference, for example if you want to open a sheet in -awakeFromNib .


An intermediate between both is to "inject" a method into the run loop:

[[NSRunLoop currentRunLoop] performSelector:@selector(methodToPerform)
target:self argument:nil order:0
modes:[NSArray arrayWithObject:NSDefaultRunLoopMode]];

or to use a NSTimer.


Well there is also the NSNotificationCenter, with which you can broadcast notifications immediately. This is a synchronous process and you can even make up a protocol, so that receivers supply the sender with return values. So this is like a method call to many different objects, you don't even know. The NSNotificationCenter is actually quite speedy, the most time is probably wasted making up the various notification objects.

As someone said this before:

message - you know (want to know) the receiver (usually coupling via procotol or interface).
notification - you don't (want) to know the receiver(s) (loose coupling, via string).

Nat!


References: 
 >Re: Notifications vs. messaging (From: Markus Hitter <email@hidden>)

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