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Overriding bind:toObject:withKeyPath:options:

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Overriding bind:toObject:withKeyPath:options:

Subject: Overriding bind:toObject:withKeyPath:options:
From: David Aames <email@hidden>
Date: Sun, 19 Nov 2006 23:16:22 +0000

Hello all,

I've been reading through the archives to see how people override bind:toObject:withKeyPath:options: when they need to implement their own bindings and the best thread which I could find is this one - http://www.cocoabuilder.com/archive/message/cocoa/2006/9/21/171579 which doesn't actually answer the question. If I send a bind:toObject:withKeyPath:options: message to a simple NSObject derived class NSObject's implementation will observe the bound-to object's property. Now here's the code from Apple which shows how they override bind:toObject:withKeyPath:options: in an NSView subclass:

- (void)bind:(NSString *)bindingName toObject:(id)observableController withKeyPath:(NSString *)keyPath options:(NSDictionary *)options { if ([bindingName isEqualToString:@"angle"]) { // observe the controller for changes -- note, pass binding identifier // as the context, so we get that back in observeValueForKeyPath:... // that way we can determine what needs to be updated. [observableController addObserver:self forKeyPath:keyPath options:nil context:AngleObservationContext]; // register what controller and what keypath are // associated with this binding [self setObservedObjectForAngle:observableController]; [self setObservedKeyPathForAngle:keyPath]; // options angleValueTransformerName = [[options objectForKey:NSValueTransformerNameBindingOption] copy]; allowsMultipleSelectionForAngle = NO; if ([[options objectForKey:NSAllowsEditingMultipleValuesSelectionBindingOption] boolValue]) { allowsMultipleSelectionForAngle = YES; } }

if ([bindingName isEqualToString:@"offset"]) { [observableController addObserver:self forKeyPath:keyPath options:nil context:OffsetObservationContext]; [self setObservedObjectForOffset:observableController]; [self setObservedKeyPathForOffset:keyPath]; allowsMultipleSelectionForOffset = NO; if ([[options objectForKey:NSAllowsEditingMultipleValuesSelectionBindingOption] boolValue]) { allowsMultipleSelectionForOffset = YES; } } [super bind:bindingName toObject:observableController withKeyPath:keyPath options:options]; [self setNeedsDisplay:YES]; }

My question is wouldn't the super implementation also start observing the key (so we end up observing it twice) or does NSView override NSObject's bind:... without using the super implementation? As far as I understand we need to call the super implementation in NSView's because the super implementation will handle the other bindings (eg "value" etc). So what are the guidelines to overriding bind:...? As far as I can see from the code we need to call the super's implementation if we inherit from NSView. But what about if we're implementing our own bindings in a class which inherits from NSObject? (eg our own NSController subclass)? Do we use the super's implemention? Or not because there are no bindings to inherit? For example if I want to create a binding in a NSObject subclass and the binding name doesn't actually correspond to the property name I would have to override bind:. The question is: do I call the super's implementation or not? (so in order to answer this question I need to know what it is doing which we can guess from the cocoa bindings docs but I want to be sure). _______________________________________________ Do not post admin requests to the list. They will be ignored. Cocoa-dev mailing list (email@hidden) Help/Unsubscribe/Update your Subscription: This email sent to email@hidden Prev by Date: Re: NSXML - preserving white space in new elements Next by Date: Re: window shadow and setAlphaValue bug? Previous by thread: Re: window shadow and setAlphaValue bug? Next by thread: Debugging complex autorelease/release/retain issue Index(es): Date Thread