Question

If I have a method like:

@interface CharacterSet
    + (NSArray *)allCharacterSets;
@end

Can I bind to it using Cocoa bindings?

I’m trying to hook up an NSComboBox’s content values to it. When I enter CharacterSet.allCharacterSets into the “Model Key Path” field in IB, it doesn’t work, saying:

[
addObserver:
forKeyPath:@”CharacterSet.allCharacterSets”
options:0x0 context:0x200275b80] was
sent to an object that is not
KVC-compliant for the “CharacterSet”
property.

I’m not sure what else to try. Currently I have to store the return value of allCharacterSets into an ivar in my custom window controller (or custom window) to make it work, which seems like an extra step I shouldn’t have to take.

Answer 1

I’m working on a huge application and the extra steps you mentioned were really pain in the ass for me. So I developed a small proxy class that handles class method bindings.

First I’ve added a small proxy class

@implementation INClassProxy

- (id)valueForUndefinedKey:(NSString *)key {
    return NSClassFromString(key);
}

@end

Then added a category accessor to NSApplication

- (id)classProxy {
    static INClassProxy *proxy = nil;
    if (proxy == nil)
        proxy = [[INClassProxy alloc] init];
    return proxy;
}

(I actually added this to my application delegate and implemented application:delegateHandlesKey:)

Now you are ready to bind class methods to the Application object, even in the interface builder, with the keyPath @"classProxy.CharacterSet.allCharacterSets".