On Jul 18, 2009, at 14:35, Brad Gibbs wrote:
- (void)addObject:(Building *)object {
[super addObject:object];
object.index = [NSNumber numberWithInt:[[self arrangedObjects]
indexOfObject:object]];
NSLog(@"Added %@", [object description]);
}
to override NSArrayController's standard implementation and assign
an index to the newly-created object, based on its index within the
underlying array. The problem is the type for the argument in the
method declaration. With the standard method signature:
- (void)addObject:(id)object
the runtime doesn't have a specific entity to look to for a
definition, so it doesn't know that I really want to be adding a
Building entity, which does have an index attribute, and it throws
an error. If I change the method declaration to:
- (void)addObject:(Building *)object
it knows that the Building entity has an index attribute, so the
error goes away. But, that means that I need to create separate
NSArrayController subclasses to control the arrays of the Floor and
Room entities. I'm hoping to find a method declaration that can
look to the entity type of the objects that the array controller is
controlling (as set in IB), so that I can use the same subclass for
the Building, Floor and Room arrays.
Oh, I get it now.
The error you're getting is nothing to do with the "runtime". The type
of the parameter variable is a compile time matter only.
If IndexedObject is the superclass of Building, Floor and Room, you
can take care of this at compile time:
- (void)addObject:(IndexedObject *)object {
[super addObject:object];
object.index = [NSNumber numberWithInt:[[self arrangedObjects]
indexOfObject:object]];
}
If it's just an entity with no custom class, you have to just make the
compiler stop complaining:
- (void)addObject:(id)object {
[super addObject:object];
[object performSelector: @selector (setIndex:) withObject:
[NSNumber numberWithInt:[[self arrangedObjects]
indexOfObject:object]]];
}
Either way, you only need one NSArrayController subclass for all 3
cases.
If you wish, you can add a check that the passed object is of the
correct class or entity.
Incidentally, it would be slightly more correct to use "NSNumber
numberWithUnsignedInteger" -- because "indexOfObject:" actually
returns a NSUInteger value, which is unsigned, and which is 64 bits in
a 64-bit app. This is not going to be a problem unless you have more
than 2 billion objects, but it's good to be prepared. :)
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