iOS App architecture implementing MVVM, Networking and Bluetooth, how? - ios

Question

Problem:
I am currently facing a problem with developing an iOS Mobile Application in Swift that utilizes:
BTLE: Connecting to a peripheral device and sending/receiving data to/from it.
Networking: If the peripheral is connected to a network (wireless and/or ethernet), then the communication over BTLE "could" instead happen over the network.
Model-View-ViewModel architecture
RxSwift
About the App:
It starts with a Bluetooth Setup view, which walks the user through the process of pairing with the peripheral device (disjoint from the TabBarController).
After successfully pairing with the device, all configuration is requested by the iOS App from the device, which is sent as JSON.
This JSON contains the different Model information (programming) that the App displays to the user for manipulation and needs to be stored in a array somehow in a Singleton manor to where a view-model can request any index for displaying to the user.
After all the data is received, the Bluetooth View dismisses and the TabBarView's are presented.
Current Examples:
A good example to relate this App to would be the Apple Watch and the correlating iOS App that allows you to configure everything. I am having to do somewhat the same concept.
Another good example app from this blog post where they are doing something similar to what I am trying to achieve. The difference I am running into though, is their dependency injection setup for MVVM (as well as other similar examples). I've used a storyboard, where as they have programmatically instantiated their view controllers in the AppDelegate.
And my problem...
How can I pass the data (efficiently) from BluetoothView to TabBarView without NSNotifications or PrepareForSegues? Keeping in mind that I am intending to use the library RxSwift for asynchronous event handling and event/data streams. I am trying to keep this App as stateless as possible.
Are the Servers in this blog post a good practice for retrieving view-models and/or updating them?

Answer 1

I find that, when using RxSwift, the "view-model" ends up being a single pure function that takes observable parameters from the input UI parameters and returns observables that are then bound to the output UI elements.
Something that really helped me wrap my head around Rx was the tutorial videos for cycle.js.
As for your specific conundrum...
What you are doing doesn't have to be "forward" movement. Look at it this way... The TabBarView needs some data, and it doesn't care where that data comes from. So give the TabBarView access to a function that returns an observable which contains the necessary data. That closure will present the Bluetooth View, make the connection, get the necessary data and then dismiss the Bluetooth View and call onNext with the required data.
Looking at this gist might help get across what I'm talking about. Granted the gist uses PromiseKit instead of RxSwift, but the same principle can be used (instead of fulfill, you would want to call onNext and then onCompletion.) In the gist, the view controller that needs the data simply calls a function and subscribes to the result (in this case, the result contains a UIImage.) It is the function's job to determine what image sources are available, ask the user which source they want to retrieve the image from and present the appropriate view controller to get the image.
The current contents of the gist are below:
//
// UIViewController+GetImage.swift
//
// Created by Daniel Tartaglia on 4/25/16.
// Copyright © 2016 MIT License
//
import UIKit
import PromiseKit
enum ImagePickerError: ErrorType {
case UserCanceled
}
extension UIViewController {
func getImage(focusView view: UIView) -> Promise<UIImage> {
let proxy = ImagePickerProxy()
let cameraAction: UIAlertAction? = !UIImagePickerController.isSourceTypeAvailable(.Camera) ? nil : UIAlertAction(title: "Camera", style: .Default) { _ in
let controller = UIImagePickerController()
controller.delegate = proxy
controller.allowsEditing = true
controller.sourceType = .Camera
self.presentViewController(controller, animated: true, completion: nil)
}
let photobinAction: UIAlertAction? = !UIImagePickerController.isSourceTypeAvailable(.PhotoLibrary) ? nil : UIAlertAction(title: "Photos", style: .Default) { _ in
let controller = UIImagePickerController()
controller.delegate = proxy
controller.allowsEditing = false
controller.sourceType = .PhotoLibrary
self.presentViewController(controller, animated: true, completion: nil)
}
let cancelAction = UIAlertAction(title: "Cancel", style: .Cancel, handler: nil)
let alert = UIAlertController(title: nil, message: nil, preferredStyle: .ActionSheet)
if let cameraAction = cameraAction {
alert.addAction(cameraAction)
}
if let photobinAction = photobinAction {
alert.addAction(photobinAction)
}
alert.addAction(cancelAction)
let popoverPresentationController = alert.popoverPresentationController
popoverPresentationController?.sourceView = view
popoverPresentationController?.sourceRect = view.bounds
presentViewController(alert, animated: true, completion: nil)
let promise = proxy.promise
return promise.always {
self.dismissViewControllerAnimated(true, completion: nil)
proxy.retainCycle = nil
}
}
}
private final class ImagePickerProxy: NSObject, UIImagePickerControllerDelegate, UINavigationControllerDelegate {
let (promise, fulfill, reject) = Promise<UIImage>.pendingPromise()
var retainCycle: ImagePickerProxy?
required override init() {
super.init()
retainCycle = self
}
#objc func imagePickerController(picker: UIImagePickerController, didFinishPickingMediaWithInfo info: [String : AnyObject]) {
let image = (info[UIImagePickerControllerEditedImage] as? UIImage) ?? (info[UIImagePickerControllerOriginalImage] as! UIImage)
fulfill(image)
}
#objc func imagePickerControllerDidCancel(picker: UIImagePickerController) {
reject(ImagePickerError.UserCanceled)
}
}