Simple example of replacing the delegate pattern with Observable pattern.

RxDelegate.swift

//
//  UITextView+Rx.swift
//  bodytonic-ios
//
//  Created by Desmond McNamee on 2017-02-04.
//  Copyright © 2017 Stadium Studio. All rights reserved.
//

import Foundation
import UIKit
import RxSwift
import RxCocoa

extension Reactive where Base: UITextView {
    public var proxy: DelegateProxy {
        return RxUITextViewDelegateProxy.proxyForObject(base)
    }
    
    public var shouldReturn: ControlEvent<Void> {
        let source = proxy
            .methodInvoked(#selector(UITextViewDelegate.textViewDidEndEditing(_:)))
            .mapToVoid()
        
        return ControlEvent(events: source)
    }
}

class RxUITextViewDelegateProxy: DelegateProxy, UITextViewDelegate, DelegateProxyType {
    
    class func currentDelegateFor(_ object: AnyObject) -> AnyObject? {
        let textView: UITextView = (object as? UITextView)!
        return textView.delegate
    }
    
    class func setCurrentDelegate(_ delegate: AnyObject?, toObject object: AnyObject) {
        let textView: UITextView = (object as? UITextView)!
        textView.delegate = delegate as? UITextViewDelegate
    }
}