Photo Writer - Sample Rx wrapper around the global function UIImageWriteToSavedPhotosAlbum

PhotoWriter.swift

import Foundation
import UIKit
import RxSwift

class PhotoWriter: NSObject {
  typealias Callback = (NSError?)->Void
  let disposeBag = DisposeBag()
  
  private var callback: Callback
  init(callback: @escaping Callback) {
    self.callback = callback
  }
  
  static func save(_ image: UIImage) -> Observable<Void> {
    return Observable<Void>.create { (observer) -> Disposable in
      let writer = PhotoWriter(callback: { error in
        if let error = error {
          observer.onError(error)
        } else {
          observer.onCompleted()
        }
      })
      
      UIImageWriteToSavedPhotosAlbum(image, writer, #selector(PhotoWriter.image(_:didFinishSavingWithError:contextInfo:)), nil)
      
      return Disposables.create()
    }
  }
  
  @objc func image(_ image: UIImage, didFinishSavingWithError error: NSError?, contextInfo info: UnsafeRawPointer) {
    callback(error)
  }
}