On Sep 17, 2008, at 14:24, dreamcat7 wrote:
NSMutableArray* dates;
NSMutableArray* emails;
[self bind:@"dates" toObject:itemsController
withKeyPath:@"arrangedObjects.date" options:nil];
[self bind:@"emails" toObject:itemsController
withKeyPath:@"arrangedObjects.email" options:nil];
Why is a binding to arrayController.arrangedObjects.itemKey only a 1-
way binding?
Can i bind to the above keypath somehow bidirectionally ?
This has been discussed on this list several times in the last couple
of months.
The short answer is that 'bind:toObject:withKeyPath:options:' doesn't
create a binding. In particular, the first parameter (where you have
@"dates" or @"emails") is not a property key but a binding name. You
need to define a binding of that name before you can use
'bind:toObject:withKeyPath:options:'.
'bind:toObject:withKeyPath:options:' is actually a method in the
NSKeyValueBindingCreation informal protocol, so it's really something
you may implement when defining a new binding, not something you
override.
The confusing part is that NSObject provides a default implementation
of this method, and if you use it with a property key as the first
parameter, you'll get what appears to be a "1-way binding".
The other confusing part is that "creating" a binding is ambiguous.
Sometimes it's used to mean "exposing" a binding -- defining the set
of behaviors that implement a binding of a certain name. Other times
it's used to mean "establishing" a binding -- using a defined binding
of a given name to link two specific objects.
The only documentation I know about for defining new bindings is:
http://developer.apple.com/documentation/Cocoa/Conceptual/CocoaBindings/Concepts/HowDoBindingsWork.html
but it's probably not worth doing unless you want to expose the new
bindings as something reusable in IB.
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