README.md

Lesson 4.2: BehaviorSubject

Problem statement

Modify the solution to Lesson 4.1 such that view.backgroundColor reflects the reachability status immediately, without having to wait for a change in reachability status.

Problem project

You can use the project in the problem folder of this repo as a starting point.

I have added a dependency against Reachability.swift to the Cartfile, and I have pulled in a copy of ReachabilityService.swift from RxExample.

Note: I have omitted the Carthage folder from the problem project, because it includes large binary files. In order to use the this project, you will need to run carthage update --platform iOS.

Solution

Discussion:

We create a new object RxReachabilityService which is a slight variation on the ReachabilityService from RxExample.

The primary changes are:

• We use a BehaviorSubject rather than a PublishSubject, which will immediately send the current value to an observer when it subscribes. This solves our problem from Lesson 4.1 of the background being white until the reachability status changed.
• We pass through the underlying Reachability.NetworkStatus enum, allowing subscribers to distinguish between Wifi and WWAN.

import RxSwift
import RxCocoa
import Reachability

class RxReachabilityService
{
    static let sharedInstance = RxReachabilityService()
    
    var reachabilityChanged: Observable<Reachability.NetworkStatus> {
        get {
            return reachabilitySubject.asObservable()
        }
    }
    
    init()
    {
        try! reachability = Reachability.reachabilityForInternetConnection()

        let up = reachability.currentReachabilityStatus
        reachabilitySubject = BehaviorSubject<Reachability.NetworkStatus>(value: up)

        let reachabilityChangedClosure: (Reachability) -> () =  { [weak self] (reachability) in
            self?.reachabilitySubject.on(.Next(reachability.currentReachabilityStatus))
        }
        
        reachability.whenReachable = reachabilityChangedClosure
        reachability.whenUnreachable = reachabilityChangedClosure
        
        try! reachability.startNotifier()
    }
    
    private let reachability: Reachability
    private let reachabilitySubject: BehaviorSubject<Reachability.NetworkStatus>
}

Our ViewController has only superficial changes from Lesson 4.1:

ViewController.swift:

import UIKit

class ViewController: UIViewController {

    private let disposeBag = DisposeBag()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        RxReachabilityService.sharedInstance.reachabilityChanged.map { (status) -> UIColor in
            switch status
            {
            case .ReachableViaWiFi:
                fallthrough
            case .ReachableViaWWAN:
                return UIColor.greenColor()
            case .NotReachable:
                return UIColor.redColor()
            }
        }.subscribeNext { [weak self] (color) -> Void in
            self?.view.backgroundColor = color
        }.addDisposableTo(disposeBag)
    }

}

Start up the app in the simulator and verify that the background color immediately relfects the current reachability status of your Mac.

New concepts to explore

• Open up RxExample.xcodeproj
  • Read through PublishSubject.swift
  • Read through BehaviorSubject.swift

Solution project

My solution is included in the solution folder of this repo.

Note: I have omitted the Carthage folder from the solution project, because it includes large binary files. In order to run the this project, you will need to run carthage update --platform iOS.