Ric,
There is a very good tutorial from Cocoa Dev Central regarding
delegates: http://cocoadevcentral.com/articles/000075.php
And from that article there is a link to another good article as well:
http://www.stepwise.com/Articles/Technical/2000-03-03.01.html
As mentioned in the articles, delegates are used for notification of
events that are about to happen. The prospect of "sharing data
between controllers" doesn't sound like a good design. The model(s)
in your application should handle the storage and access of the data,
your controllers will interact with the model in order to read or
modify that data. You may have more than one controller accessing the
same model, but various controllers don't necessarily send data back
and forth between each other, they can send messages to other
controllers and their views though.
--
Evan
On Aug 14, 2009, at 5:24 PM, Frederick C. Lee wrote:
Environment: iPhone (but Cocoa as well)... I was using the App
Delegate
as the link amongst view controllers in sharing data. The 'App
Delegate',
being persistent,
was my 'global data' clearing house.
But now I learned that this is frown upon. The preferred way
is using
delegation to share data.
From what I've read, delegation is essentially shared procedures
via an
informal protocol; albeit the preferred design is to use
the formal protocol with @optional & @required directives.
I think I understand the basics.
But I wonder, how is data actually SHARED between a view controller
and its
delegate?
The view controller has an ivar of type 'id' for the delegate, which
has
methods declared within the protocol.
Here's some elementary questions:
1) How is the delegate actually launched (with valued parameters)?
2) How does the calling controller receive data back from the
delegate?
Regards,
Ric.
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