Question-about-self-and-delegates

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Date: Sun 30-Aug-1991 09:01:34 
From: carlton@cs.berkeley.edu (Mike Carlton)
Subject: Question about self and delegates

I've got a question for the obj-c gurus:

I'm playing around with a simple text editor, trying to get my feet
wet.  I've got a Document class and I define a delegate method
window.  So it looks something like this:

@interface Document:Object
{
        id window;
        id scrollview;
        id text;
        const char *name;
        int titled;
}
..
@end

@implementation Document

- init
{
	...
        [window setDelegate:self];
}

- windowWillClose:sender
{
        if ([window isDocEdited]) {
	...
        }

        return self;
}

@end

I would expect that within the windowWillClose: method self would
be a Document (after all, it is defined as a Document method).

_But_, at runtime, self within windowWillClose: is a FrameView ?!
(i.e. p self->isa->name returns "FrameView").  Now sender (which
is a Window) has the correct delegate -- p sender->delegate->isa->name
returns "Document".

Why isn't self a Document?  gdb thinks it should be a Document: if
you enter p self it prints '(struct Document *) 0x72f58'.  If you
print *self, you get a bunch of bogus values (because *self is really
a FrameView).  Can anyone tell me what is going on?  What am I 
missing?

thanks in advance,
mike (carlton@cs.berkeley.edu)

Date: Sun 04-Sep-1991 03:18:35 
From: wiml@milton.u.washington.edu (William Lewis)
Subject: Re: Question about self and delegates

In article <1991Aug30.090134.2292@agate.berkeley.edu> carlton@cs.berkeley.edu writes:
>I'm playing around with a simple text editor, trying to get my feet
>wet.  I've got a Document class and I define a delegate method
>windowWillClose: and set the document to be the delegate for the
>window.  So it looks something like this:

...

>@implementation Document
>
>- init
>{
>	...
>        [window setDelegate:self];
>}

   This could be the problem. The usual method of generating a new object
in the absence of the +new method is 

   anObj = [[Something alloc] init];

   Notice that your -init method isn't explicitly returning anything. The
caller will get a garbage value, which I suppose happens to be a
FrameView. Because of the way function returns are implemented by the
compiler, this is probably the old delegate, unless I'm forgetting
something (entirely possible). Thus the window's delegate variable
would be set to the 'real' self (since you just passed it) but immediately
afterwards the self would be lost.

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