RxDelegate.swift

extension ImagePreheatingController {
  public var rx_delegate: DelegateProxy {
    return proxyForObject(RxImagePreheatingControllerDelegateProxy.self, self)
  }
  
  public var rx_preheatItems: Observable<([Int], [Int])> {
      return rx_delegate.observe("preheatingController:didUpdateWithAddedIndexPaths:removedIndexPaths:")
        .map { a in
          print(a)
          return ([], [])
        }
        .startWith(([], []))
    }
}


class ImagePreheatingControllerDelegateNotSet:
  NSObject,
  ImagePreheatingControllerDelegate {
  func preheatingController(controller: ImagePreheatingController, didUpdateWithAddedIndexPaths addedIndexPaths: [NSIndexPath], removedIndexPaths: [NSIndexPath]) {
  }
}

private let delegateNotSet = ImagePreheatingControllerDelegateNotSet()

class RxImagePreheatingControllerDelegateProxy :
  DelegateProxy,
  DelegateProxyType,
  ImagePreheatingControllerDelegate {
  
  private weak var _requiredMethodsDelegate: ImagePreheatingControllerDelegate? = delegateNotSet
  
  
  class func currentDelegateFor(object: AnyObject) -> AnyObject? {
    let preheatingController = object as! ImagePreheatingController
    return preheatingController.delegate
  }
  
  class func setCurrentDelegate(delegate: AnyObject?, toObject object: AnyObject) {
    let preheatingController = object as! ImagePreheatingController
    preheatingController.delegate = delegate as? ImagePreheatingControllerDelegate
  }
  
  override func setForwardToDelegate(forwardToDelegate: AnyObject?, retainDelegate: Bool) {
    let requiredMethodsDelegate = forwardToDelegate as? ImagePreheatingControllerDelegate
    _requiredMethodsDelegate = requiredMethodsDelegate ?? delegateNotSet
    super.setForwardToDelegate(forwardToDelegate, retainDelegate: retainDelegate)
  }
  
  func preheatingController(controller: ImagePreheatingController, didUpdateWithAddedIndexPaths addedIndexPaths: [NSIndexPath], removedIndexPaths: [NSIndexPath]) {
    (_requiredMethodsDelegate ?? delegateNotSet).preheatingController(controller, didUpdateWithAddedIndexPaths: addedIndexPaths, removedIndexPaths: removedIndexPaths)
  }
}