README.md

Lesson 3.7: timer

Problem statement

Write an app which spits out a single "hello" message after a 3 second delay, using func timer.

Problem project

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

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

ViewController.swift:

import UIKit
import RxSwift
import RxCocoa

class DelayedSingleHelloGenerator
{
    class func generate() -> Observable<String>
    {
        let delayedObservable = timer(3, MainScheduler.sharedInstance)
        
        let helloObservable = delayedObservable.map({ (_) -> String in
            return "hello"
        })
        
        return helloObservable
    }
}

class ViewController: UIViewController {

    let disposeBag = DisposeBag()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        DelayedSingleHelloGenerator.generate().subscribeNext { (s) -> Void in
            debugPrint(s)
        }.addDisposableTo(disposeBag)
    }
}

Discussion:

Here, we use func timer to generate a single Event after a 3 second delay, which we then map to a "hello" message.

Start up the app and verify that you see a single "hello" after a 3 second delay:

"hello"

The timer function also has a second interface which includes an initial delay value. We can combine the functionality of lesson 3.6 and 3.7 together to generate an infinite stream of one-second interval "hello" messages which start after a 3 second delay:

class DelayedTickHelloGenerator
{
    class func generate() -> Observable<String>
    {
        let tickerObservable = timer(3.0, 1.0, MainScheduler.sharedInstance)
        
        let helloObservable = tickerObservable.map { (_) -> String in
            return "hello"
        }
        
        return helloObservable
    }
}

New concepts to explore

• Open up RxExample.xcodeproj.
  • Take a look at func timer in Observable+Creation.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.