lesson3.1_generate

Lesson 3.1: generate

Problem statement

Write an app which spits out an infinite series of "hello" messages to the debugging console.

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 InfiniteHelloGenerator
{
    class func generate() -> Observable<String>
    {
        return RxSwift.generate("hello",
                condition: { (_) -> Bool in return true},
                iterate: { (s) -> String in return s })
    }
}

class ViewController: UIViewController {

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

Discussion:

We introduce func generate(), use it to create an Observable<String>, and our ViewController subscribes to its stream of Event<String>.

Start up the app and verify that you see an infinite stream of "hello" in the console:

"hello"
"hello"
"hello"
...

What's going on here? A slightly more verbose version of InfiniteHelloGenerator will be illustrative:

class VerboseInfiniteHelloGenerator
{
    class func generate() -> Observable<String>
    {
        return RxSwift.generate("hello", condition: { (s) -> Bool in
            
            debugPrint("condition closure.  s: \(s)")
            return true
            
        }, iterate: { (s) -> String in
            
            debugPrint("iterate closure.  s: \(s)")
            return s
            
        })
    }
}

Hook that up to ViewController, fire that up in the simulator and you should see this in the console:

"condition closure.  s: hello"
"hello"
"iterate closure.  s: hello"
"condition closure.  s: hello"
"hello"
"iterate closure.  s: hello"
"condition closure.  s: hello"
"hello"
"iterate closure.  s: hello"
...

New concepts to explore

• Open up RxExample.xcodeproj.
  • Take a look at func generate 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.