CODEWITHSUNDEEP
cocoapropertieskey-value-coding
Richard
Richard

Reputation: 3386

Forwarding property accessors to an ivar's method

I have a panel that elaborates on the selected table row. Obviously, the panel's display often needs updating, and I've pushed that task off to an NSWindowController subclass.

I would like the custom NSWindowController to have @propertys for things like the string values in the text fields and the image values in the NSImageViews. Because I need no novel code in the accessors, I want to @synthesize them. Unfortunately (for me), there is no option to use key-paths in @synthesize property=ivar.

The obvious solution is to write my own accessors of the form

- (void)setTitle:(NSString *)title
{
    [titleTextField setStringValue:title];
}

- (NSString *)title
{
    return [titleTextField stringValue];
}

but I'd rather not have to do that by hand for each of several properties.

Is there a simpler way? Perhaps a generic way to set up a property to forward to a specific property (except objectValue etc. aren't actually proper properties) of another object?

Upvotes: 0

Views: 125

Answers (3)

hooleyhoop
hooleyhoop

Reputation: 9198

You have a contradiction, you say you need no novel code in the accesors so you'd like to synthesise them, but the code you need is completely novel. Properties are syntactic sugar for a few common cases, of which this isn't one.

There are several ways to do what you want, eg. as @Justin suggests overriding setvalue:forundefinedkey: - you just need a lookup of forward targets, but the sugar of properties isn't a good fit for this.

Upvotes: 0

Mike Weller
Mike Weller

Reputation: 45598

I don't think doing any kind of forwarding is going to be useful since the property names on the textfield are going to be different to the ones on your class.

Abstracting away from the textfield by exposing a string property is of course a good idea, but if you want to avoid writing this boiler plate you may find it acceptable to simply expose the text field itself as a property. You can see this in some of Apples APIs, particularly on the iPhone where in SDK 3.0 instead of having properties like text on a table cell they now have textLabel. It's simpler and allows more customization if a callee wants to customize a label or text field in some way.

Upvotes: 0

Justin Spahr-Summers
Justin Spahr-Summers

Reputation: 16973

If you implement valueForUndefinedKey: in your class, you should get a last chance to resolve any key-value path lookups and forward them all to the other object. This is certainly not performant, though, and will only give you significant gains if most of the property names that you're passing through match those of the target object.

Upvotes: 1

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