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Re: NSCoding protocol
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Re: NSCoding protocol


  • Subject: Re: NSCoding protocol
  • From: Negm-Awad Amin <email@hidden>
  • Date: Fri, 10 Oct 2008 18:09:01 +0200


Am Fr,03.10.2008 um 21:00 schrieb email@hidden:

I want MyClass to conform to the NSCoding protocol. But I'm puzzled about how to implement the initWithCoder: method.

Suppose I have this in MyClass.h:

	NSString *S1, *S2, *S3;


and this in its init function:

	S1 = @"a string";
	S2 = [[NSString alloc] init];
	S3 = [NSString string];

So to conform to the protocol, I'd have something like this in MyClass.m too:
In addition to the replies I want to give a hint to something else:

- (id)initWithCoder:(NSCoder *)decoder {

self = [super init];
This is only correct, if your base class does not support NSCoding. Otherwise you have to call -initWithCoder: (super).

Because this depends of the base class, we have a fragile base class problem. (Adding NSCoding to the base class looks like doing everything correct inside the base class, but will cause MyClass as a subclass to a malfunction.) Keep in mind, that NSCoding can be added through a category. So it looks safer to do:

if( [super respondsToSelector:@selector( initWithCoder: )] {
   self = [super initWIthCoder:decoder];
} else {
   self = [super init];
}

I never had this problem in practice, but theoretically … (But maybe I got a paranoia.)

Cheers






	S1 = [decoder decodeObjectForKey:@"S1"];
	S2 = [[decoder decodeObjectForKey:@"S2"] retain];
	S3 = [[decoder decodeObjectForKey:@"S3"] retain];
	return self;
}

(I'm not posting the encodeWithCoder: method.)

So finally, my question: am I right to retain S2 and S3, and not S1?
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Amin Negm-Awad email@hidden




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