On Jun 28, 2008, at 4:55 AM, Ken Thomases wrote:
Yeah, it surprises me, too, that NSObject has an implementation of
bind:toObject:withKeyPath:options:. I had thought that it was just
part of an informal protocol -- that is, that it was declared in a
category on NSObject, but never implemented except by specific
classes which adopted that protocol. However, I did a symbol dump
of the AppKit framework and I see that there is, in fact, an
implementation. I have no idea what it could be doing.
Actually, I gave it a little thought, and perhaps the purpose of
NSObject's default implementation is just to make it easier to
implement the stuff that's mentioned in that "how bindings work"
document. The built-in implementation provides the bindings in one
direction for us - all we have to do is supply the bindings in the
other direction, so adding an NSMutableDictionary instance variable to
the view and then adding these methods:
- (void)bind:(NSString *)key toObject:(id)obj withKeyPath:(NSString
*)keyPath options:(NSDictionary *)options {
NSDictionary *binding = [NSDictionary
dictionaryWithObjectsAndKeys:key, @"key", obj, @"target", keyPath,
@"keyPath", nil];
[ivar_bindingsDict setObject:binding forKey:key];
[super bind:key toObject:obj withKeyPath:keyPath options:options];
}
- (void)unbind:(NSString *)key {
[ivar_bindingsDict removeObjectForKey:key];
}
- (void)fireNotificationsForKey:(NSString *)key {
NSDictionary *binding = [ivar_bindingsDict objectForKey:key];
if(binding) {
id target = [binding objectForKey:@"target"];
NSString *keyPath = [binding objectForKey:@"keyPath"];
[target setValue:[self valueForKey:key] forKeyPath:keyPath];
}
}
and then just calling [self fireNotificationsForKey:@"someKey"] each
time you modify whatever it is in the view's state that will cause the
binding "someKey" to need to be updated, would pretty much do it, am I
right?
(I suppose you'd also want to expose your available bindings by
calling +exposeBinding: in your +initialize method and implement
valueClassForBinding: if you're going to make an Interface Builder
palette for your view)
Charles
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