UICollectionViewDelegate in RxCocoa - rx-swift

Question

I write an extension for UICollectionView which will listen the delegate's
shouldHighlightItemAt method,but it don't call.
public var shouldHighlightItem: ControlEvent<IndexPath> {
let source = self.delegate.methodInvoked(#selector(UICollectionViewDelegate.collectionView(_:shouldHighlightItemAt:)))
.map { a in
return try self.castOrThrow(IndexPath.self, a[1])
}
return ControlEvent(events: source)
}
}
how to write an extension for UICollectionView of rx shouldHighlightItemAt?

Answer 1

You cannot use methodInvoked(_:) with a delegate method that has a non void return type.
collectionView(_:shouldHighlightItemAt:) expects you to return a Bool value. So you cannot use methodInvoked(_:).
If you have a look at the implementation of methodInvoked(_:) it gives you an explanation why this does not work:
Delegate methods that have non void return value can't be observed
directly using this method
because:
those methods are not intended to be used as a notification mechanism, but as a behavior customization mechanism
there is no sensible automatic way to determine a default return value
There is however a suggestion how you could achieve what you are trying to do:
In case observing of delegate methods that have return type is
required, it can be done by
manually installing a PublishSubject or BehaviorSubject and implementing delegate method.
In your case it would work like this:
In RxCollectionViewDelegateProxy you add the 'PublishSubject' and implement the UICollectionViewDelegate method:
let shouldHighlightItemAtIndexPathSubject = PublishSubject<IndexPath>
public func collectionView(_ collectionView: UICollectionView, shouldHighlightItemAt indexPath: IndexPath) -> Bool {
shouldHighlightItemAtIndexPathSubject.on(.next(indexPath))
return self._forwardToDelegate?.collectionView(collectionView, shouldHighlightItemAt: indexPath) ?? true // default value
}
In your UICollectionView RxExtension you can expose the desired Observable like this:
public var property: Observable<IndexPath> {
let proxy = RxCollectionViewDelegateProxy.proxy(for: base)
return proxy.shouldHighlightItemAtIndexPathSubject.asObservable()
}
I have not tested this, I merely took it from the RxCocoa source code and modified it to fit your needs. So in theory this should work, but you might have to tweak it a little bit ;-)