Binding selected radiobox to enabling checkbox in Cocoa - xcode

Question

I haven't worked with Cocoa bindings a lot before, so I would need a little help here.
I have a radio button group ( NSMatrix ) with three buttons and one checkbox.
I want the checkbox to be enabled only when the last radio button is selected.
Found a tutorial online which advised to bind the selected tag property of the radio button group to the enabled property of the checkbox. The last radiobutton needs to have a tag of 1, the others would need to have a tag of 0.
This works great.
The problem is, that if the checkbox is checked and the radiobutton selection is changed, it stays checked although it isn't enabled. I would want that the box gets unchecked when it changes to the disabled state.
Any advise would be appreciated!
Thanks in advance!
Any way to achieve this without any code?

Answer 1

I doubt it's possible to do this without code.
I handle this in the model, using KVO. Code looks something like this:
-(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context {
if ([#"checkWithInProcess" isEqualToString:keyPath]) {
NSNumber *oldValue = [change objectForKey:NSKeyValueChangeOldKey];
NSNumber *newValue = [change objectForKey:NSKeyValueChangeNewKey];
BOOL oldValueAsBool = (oldValue != (id)[NSNull null]) && oldValue.boolValue;
BOOL newValueAsBool = (newValue != (id)[NSNull null]) && newValue.boolValue;
if (oldValueAsBool && !newValueAsBool) {
// Save the value
savedRecordValueWithInProcess = self.recordValueWithInProcess;
self.recordValueWithInProcess = nil;
} else if (!oldValueAsBool && newValueAsBool) {
// Restore the value or set it to the default
if (savedRecordValueWithInProcess)
self.recordValueWithInProcess = savedRecordValueWithInProcess;
else
self.recordValueWithInProcess = [NSNumber numberWithBool:NO];
savedRecordValueWithInProcess = nil;
}
}
}
And during initialization:
[self addObserver:self
forKeyPath:#"checkWithInProcess"
options:NSKeyValueObservingOptionOld | NSKeyValueObservingOptionNew
context:[Characteristic class]];