On Jul 3, 2009, at 01:20, Bill Cheeseman wrote:
In the case of buttons, you likewise have to implement - validateUserInterfaceItem: yourself. But that isn't enough, because Cocoa does not call it automatically just because you implemented it. A generic solution is to implement the -windowDidUpdate: delegate method in your window controller, and in it loop through all the subviews in your window's contentView. In each iteration of the loop, call your -validateUserInterfaceItem: method, testing first to make sure the item implements -action and -tag and - setEnabled: (or just test whether it's a button, since all buttons do). If efficiency becomes a problem, take steps to reduce the frequency with which -validatedUserInterfaceItem: is called (every time the window updates -- that is, once every time through the run loop -- may be overkill for many validation scenarios).
You should test for the specific view classes you want to have validated (just NSButton, I think, but I may have missed something from earlier in the thread). Don't try to initiate validation on every item (even if it implements action, tag and setEnabled), because you don't know for sure what other classes may already have validation systems in place (like menus and toolbars do, though they of course won't be found among the subviews).
I would also check that the button *doesn't* conform to NSValidatedUserInterfaceItem, because if it does that certainly means it is already participating in a validation system being initiated elsewhere. There don't appear to be any such systems (apart from menus and toolbars) in the Cocoa frameworks under Leopard, but who knows what may change in the future?
Then the only danger is that if someone else (e.g. a 3rd-party framework) implements a validation system for NSButtons in the same ad- hoc way you're proposing, then your two systems will conflict. However, if that's the case, you probably won't know of it (except that validation will occur twice as many times), and there's not much you can do about it, so it's not worth worrying about.
When you invoke validateUserInterfaceItem:, your window controller also needs to make sure to send the message to the button's effective target, not to self, similar to what's described in:
http://developer.apple.com/documentation/Cocoa/Conceptual/UIValidation/Articles/ValidatingObjects.html#/ /apple_ref/doc/uid/20000745
so the code will look a bit like this:
id validator = [NSApp targetForAction:[button action] to:[button target] from: button]; if ((validator == nil) || ![validator respondsToSelector:[button action]])[button setEnabled:NO];else if ([validator respondsToSelector:@selector(validateUserInterfaceItem:)]) [button setEnabled:[validator validateUserInterfaceItem: (id< NSValidatedUserInterfaceItem>) button]];else [button setEnabled:YES];
I agree that the frequency of the validation is a side issue, to be dealt with if there is a problem. In general, there may also be a problem with validation *not* getting called unless there is a window update, if the validation result might change when there is no visible change to the window. (I believe there's a flaw like that in the toolbar automatic validation, but I've never been able to pin it down.)
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