Re: superclass and awakeFromNib

FROM : Fritz Anderson
DATE : Sat Nov 30 19:36:14 2002

When -[DummyViewA awakeFromNib] is called with [aDummyViewB
awakeFromNib],  the "self" pointer still points to an instance of
DummyViewB. Therefore [self superclass] will be DummyViewA.

Keep repeating to yourself: Objective-C messages are resolved at run
time, not compile time.

"super," however, still refers to the implementation in the superclass
of the current implementation, which is why your code attempts to send
-[NSView awakeFromNib], and fails.

What you do know at compile time is what classes you're implementing
awakeFromNib for, what the superclass of each class is, and that NSView
does not implement awakeFromNib, It isn't cheating to simply send
[super awakeFromNib] in -[DummyViewB awakeFromNib] and not send it in
-[DummyViewA awakeFromNib].

   -- F

On Saturday, November 30, 2002, at 10:52  AM, Simon Bovet wrote:

> @interface DummyViewA : NSView {
> }
> @end
>
> @interface DummyViewB : NSViewA {
> }
> @end
>
> @implementation DummyViewA            // same for DummyViewB
>
> -(void)awakeFromNib
> {
>      if ([[self superclass]
> instancesRespondToSelector:@selector(awakeFromNib)])
>          [super awakeFromNib];
> }
>
> @end
>
> When [DummyViewB awakeFromNib] is performed during program execution,
> it works fine and calls [DummyViewA awakeFromNib]. Now, [self
> superclass] in DummyViewA returns DummyViewA (!) and [super
> awakeFromNib] throws the exception "*** -[DummyViewB awakeFromNib]:
> selector not recognized".
>
  --
Fritz Anderson - Consulting Programmer - Chicago, IL
Mail:        <<email_removed>>
Risumi:    <http://resume.manoverboard.org>
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