RxSwift Glossary and Concepts

Do you speak RxSwift? Do you know the concepts, words and operators? Here is a snapshot summary of many of them.

Some of the RxSwift Concepts from Getting Started

An Observable is a definition of: 

  • “..how the sequence is generated..”
  • “..what parameters are used for element generation..”

Disposing

“..release all of the resources that were allocated to compute upcoming elements..”

Observable aka Sequence

  • One after another, the Observable sends a Next (element), Error, or a Completed
  • What stops them from coming? An Error, Completed or dispose the subscriptions.

Observer

Subscribes to Observables

Subject

(Source: Rx.playground)

Terse mode: “acts both as an Observer and as an Observable”

Full mode: “A Subject is a sort of bridge or proxy that is available in some implementations of ReactiveX that acts both as an observer and as an Observable. Because it is an observer, it can subscribe to one or more Observables, and because it is an Observable, it can pass through the items it observes by reemitting them, and it can also emit new items.”

Operators

There is a list sorted by functionality at https://github.com/ReactiveX/RxSwift/blob/master/Documentation/API.md#rxswift-supported-operators

Operator Types:

(Sources: Rx.playground and github docs)

  • Combination operators – startWithcombineLatestmergeswitchLatestzip; “Operators that work with multiple source Observables to create a single Observable”
  • Conditional and Boolean Operators – takeUntiltakeWhile – “Operators that evaluate one or more Observables or items emitted by Observables.”
  • Connectable Observable Operators – multicastreplay, replayAll, publish – “like an ordinary Observable yet only when its connect() is called does it emit”
  • Error Handling Operators- catchErrorretry – “Operators that help to recover from error notifications from an Observable.”
  • Filtering Observables – distinctUntilChanged, filtertake; “Operators that selectively emit items from a source Observable.”
  • Mathematical and Aggregate Operators – concat, reduce – “Operators that operate on the entire sequence of items emitted by an Observable”
  • Observable Utility Operators – doOn, subscribesubscribeNextsubscribeCompletedsubscribeError; “toolbox of useful Operators for working with Observables”
  • Transforming Observables – map / selectflatMapscan; “Operators that transform items that are emitted by an Observable”
  • Units – “purpose of Driver unit is to ensure the underlying observable sequence has the following properties”: It “can’t fail”, “main thread”, and more.

Schedulers

Schedulers are an abstraction away from what does work (queues / threads).

RxSwiftCommunity

By the way, the RxSwiftCommunity bears checking in on from time to time. Action is listed there and it comes up often in the RxSwift Slack community and at least once in Stack Overflow. Just like the adoption of RxSwift, I sense the community will grow over time.

Update: If one looks at the code commits done for the RxSwiftCommunity website, one can easily see lots of activity going on.

RxSwift and Memory

Tom Burns asked a good question about TableView bindings outliving the view controller. As he said:

I’m asking because I noticed that some of my tableview bindings were outliving the view controller being popped back off the stack and it seemed like unnecessary work was being done…

kzaher of the RxSwift Slack community pointed out the following code as being the culprit:

Tom fixed the code to use an “[unowned self]” before the newObjects. Such as:

Although such memory situations aren’t limited to RxSwift, using RxSwift might encourage such situations to come up more often. It something to watch out for.

Regardless, this is something we all can run into from time to time. I feel fortunate enough to have caught the conversation in the RxSwift Slack community and am grateful to Tom for asking.

Simpler RxSwift Test Code

Looking at some RxSwift test code, I knew it could be better. As I shared with Krunoslav Zaher aka kzaher in the RxSwift Slack community:

I feel the opportunity for improvement down to my soul.

Test Code
He kindly helped me simplify some RxSwift test code. He suggested that instead of:

Do something like this:

To make that work, I had to change the oldBakeryServiceSpy from something like this:

To this:

This also allowed us to use failWith. As in:

 

More kzaher Words of Wisdom

if you are mocking, just use just, sequenceOf, [].toObservable()

It was also shared that TestScheduler will be released soon and one can look at the unit tests.

What about Simplifying Our Use of the DisposeBag?

As a result of what we read in the README, we use DisposeBag objects often. As kzaher shared:

If you use operators, that will reduce the amount of dispose bags significantly. We handle all of disposing for you. You only dispose terminal endpoints where you do “subscribe”

All Part of the Game of Learning

Slowly things are improving. Although it’s all part of the game of learning something new, I think it would serve all well if someone created a game called “Simplify This RxSwift code.” I know I would happily play it.

Path to Learning FRP and RxSwift In a Nutshell

This is some of what I did to learn FRP / RxSwift:

The RxSwift Slack Community is awesome: http://slack.rxswift.org They guided me to these resources.

Besides playing around with lots of code, that’s the meat of what I did. I know every individual has his or her own path of learning. However, I figured I would share a terse version of mine in case it helps.

Update December 31, 2015: I would watch Functional Reactive Programming with RxSwift by Max Alexander first.

 

Learning RxSwift

Although ReactiveCocoa looked promising, it had a few things that are not yet there. These are outlined in an earlier article, ReactiveCocoa and MVVM Initial Experience. So, it was time to explore RxSwift.

I started with reading the concepts in the README. It was pretty straight forward. My next move was to find an example which is like the ReactiveCocoa oriented ReactiveTwitterSearch example that I loved so much. Where to begin? Good thing I discovered the RxSwift slack community.

Having an active slack community is a huge win! With the help of Carlos García in slack, I found GitHubSignup in the RxExample examples. This was definitely what I was looking for.

For fun, I created a small demo app which explored the bindings. I decided to see what was there for a UIPickerView and UITextView.

Compared to ReactiveCocoa, the RxSwift repo comes with extensions to some of the UIKit components. These are known as RxCocoa extensions. RxCocoa is located alongside the RxSwift code in the GitHub repository. However, if you are using CocoaPods like I am, RxSwift and RxCocoa are two separate pods.

After much searching, I discovered there is no extension made for the UIPickerView. So, I just made a PickerViewAdapter which contains a selectedPerson RxSwift Variable and PickingPersonViewModel. The adapter handles the UIPickerViewDelegate and UIPickerViewDataSource while calling through to the PickingPersonViewModel. The adapter is used by the View Controller.

With the UITextView, I had much better luck. With a simple binding, I was able to hook up a notes UITextView up with a specific note in the NotesViewModel. Changes to the UITextView would be reflected in the note. Pretty neat! Code is here:

_ = notesTextView.rx_text.subscribeNext { someText in

// Changes to notesTextView’s text triggers this block.

self.notesViewModel.currentNote().value.text = someText

}

How do extensions like rx_text work? I looked at the simplest example, the RxSwift UILabel extension. AnyObserver has an observer which is an event handler. As can be seen in the code, the UILabel extension with rx_text is an adapter that handles String events.

Although it’s currently Beta, there’s a sense that RxSwift will be out of beta soon. This is based on a Github request for it to be released as 2.0.0.

Based upon my observations and discussing it with some smart people at CARFAX I know, it looks like RxSwift is pretty solid. If you are interested in supporting MVVM in a Functional Reactive programming style, I recommend you check it out!

ReactiveCocoa and MVVM Initial Experience

The vision of Functional Reactive Programming (FRP) and specifically ReactiveCococa (RAC) 4.0 alpha are both impressive. FRP via RAC and Swift feels right. As mentioned in my previous article, RAC 4.0 is useable. Its core concepts are quite solid. Yet, one has to really want to dive in and be willing to offset any UIKit shortcomings. That’s fair since RAC 4.0 is alpha.

Where ReactiveCocoa needs more help:

  • There is a need for the ReactiveCocoa CocoaPods spec to be updated
  • There is a need for more UIKit extensions

Need for Updated ReactiveCocoa CocoaPods spec

That’s probably easy for one to do since it’s an update to an existing pod spec. If one doesn’t have time or want to, one can use Carthage as mentioned in my previous article, Swift 2 ReactiveCocoa MVVM Quest.

More UIKit Extensions

Based on a post here by Neil Pankey (a collaborator on ReactiveCocoa), Rex is a ReactiveCocoa Extensions project that eventually will get merged into ReactiveCocoa. As Neil mentions:

It’s not there yet, because “..haven’t found the time to port them, flush out the missing properties, add documentation, etc”

Although it has some extensions, more are needed. I immediately came up for the need for an extension that would let me capture text in a UITextField. Digging deeper I see in a somewhat older post, that there are many extensions that need to be ported over to Swift. Looking at Rex UIKit specific code myself, I think that’s still the case. If the community rallies around making more UIKit Extensions, it would help everyone.

To address what I needed now, I used a fork of ReactiveTwitterSearch originally made by Colin Eberhardt, and grabbed the UIKitExtensions code and a couple other items. Doing that, I was able to bind the text put into a text field straight into a View Model like so:

        loginViewModel.username <~ usernameTextField.rac_text

That line of code is quite similar to the awesome but dated article RAC 3 Properties section of MVVM with ReactiveCocoa 3.0.

So, that is neat and powerful since with some easy to read binding/configuration one is making it much easier to do MVVM. As long as you don’t mind, piecing things together and absorbing the learning curve, this power is yours for the taking now.

Swift 2 ReactiveCocoa MVVM Quest

The Quest

For a software developer (especially at CARFAX), the quest for cleaner code is worthy and eternal. In Swift and Objective-C, two main battlefields where clean code is threatened are View Controllers and client network code. View Controllers get big and client network code suffers from the Pyramid of Doom. The Pyramid of Doom is where there are many nested statements as shown in this Traditional asynchronous code slide. Following the advice of a smart friend named Mike Groner, I looked into ReactiveCocoa (RAC) and revisited MVVM.

Since we have looked at MVVM before and MVVM’s roots go way back to the Presentation Model via Martin Fowler, its concepts are not foreign. It’s true that one does not have to use RAC to do MVVM. As Natasha The Robot showed in her Swift Summit presentation and related Protocol-Oriented MVVM (POMVVM) article, one can manually follow the discipline of doing POMVVM without a framework. So, that’s great. One concern is that it requires the team to relentlessly apply discipline to do POMVVM well.

Shifting our attention to the Pyramid of Doom, how can RAC and Functional Reactive Programming in general help? To answer that question, I checked out Javier Soto‘s Back to the Futures Swift Summit presentation. It was eye opening. It discussed how we typically handle asynchronous callbacks (thus the Pyramid of Doom), error handling, and the concept of Futures as a way of getting rid of “…all the noise related to the asynchrony itself.” Easier to write, read and maintain code through Futures / Promises or better yet Signals sounds good! At the end of the talk, he also recommended ReactiveCocoa aka RAC.

So, What About ReactiveCocoa (RAC)?

OK. The message is loud and clear: Check out RAC! Natasha-The-Robot, guided me to Ash Furrow. Ash helpfully shared Functional Reactive Awesomeness With Swift So, RAC is impressive and RAC may even help one do MVVM. Which version of RAC should I investigate?

For an upcoming project, using Swift 2.1 is a no brainer. Can RAC or something similar be used in a Swift 2.1 project?  NachoSoto comes to the rescue on Twitter and Stackoverflow:  How to Add Production Ready ReactiveCocoa … Into Swift 2 iOS. So, the answer is yes!

Getting ReactiveCocoa 4.0

Being more than ready to dive into ReactiveCocoa 4.0, the question was now “how to get it?” I tried using CocoaPods, but the unofficial podspecs were out of date. it seems like a good answer is using Carthage with a Cartfile of:

github "ReactiveCocoa/ReactiveCocoa" "v4.0.0-alpha.3"

Since I have been a CocoaPods user, it didn’t immediately occur to me to copy the frameworks as per the RAC README page:

On the “General” tab of your application target’s settings, add ReactiveCocoa.framework and Result.framework to the “Embedded Binaries” section.

Success!

RAC and MVVM?

Could RAC or something like it also help with MVVM? Both my friend and Ash Furrow’s presentation above suggested that it could do so beautifully. Searching the web for the most recent ReactiveCocoa Swift examples, I found MVVM With ReactiveCocoa 3.0 by Colin Eberhart and Migrating to Swift 2 and ReactiveCocoa 4 by Martin Richter. So, it certainly seems so.

With ReactiveCocoa 4.0 and examples at hand, the journey has just begun and the quest for clean and well crafted code continues!

Meditating on Meditation Mobile Apps

For a long time, I have watched meditation apps come and go. I feel the apps have crossed a threshold of quality and reliability such that it’s ok to pony up some cash for what I see. Two have served quite well, 10% Happier: Meditation for Skeptics and Headspace.

10% Happier: Meditation for Skeptics

The content is fascinating and top notch. The daily video and meditations are short enough and thus bite sized for the busy person.

They hit on topics I care about deeply and didn’t see anywhere else. Specifically, I wanted to know if meditating would keep me from hitting goals I want to go for. I wanted to know if I would become complacent. They answer that question head-on and many other pragmatic topics. One can also replay the videos as often as desired.

Besides the Q & A sessions between Dan Harris and highly respected meditation experts such as Joseph Goldstein, it comes with guided meditations and even a personal coach who can send and receive messages.

It’s especially nice to have someone who can respond to your individual questions or an experience you want to share. Also, there is something nice about how easy it is to just send a message in the mobile app as opposed to sending emails back and forth.

Headspace

There are some really well done videos such as this “blue sky” animation titled Underlying Calm that is shown right in the app as you progress through the steps.

Other Noteworthy Items:

  • The mobile application gives you a sense of progress and accomplishment.
  • There’s a download manager in the mobile application which I found very useful.
  • You can try it for free and then subscribe to the later packs.
  • There are many other items that are great about it. I highly recommend checking out their How It Works webpage.

“Which One Should I Choose?”

Ah. Good question. I started with Headspace. However, I switched to the 10% Happier app after trying both for a year.  I found the 10% Happier app essential to getting answers to some questions I have had. If I had never tried either, I would suggest starting with the 10% Happier: Meditation for Skeptics. However, the choice is yours and you will come out ahead if you choose at least one.

Wrap Up

Although there are many meditation related apps out there, the best ones I know about are the two I covered in this article. Is there a fantastic one that I should try? Please feel free to leave a comment to share what you know or to just say hi. Good luck on your journey and be well!

Updated: December 7, 2017: I updated the Headspace video and content in this entire post.

(Unofficial) Mindful Minecraft Meditation

One day, my son looks up at me and says “Dad, I want to meditate too!”

How did my son get an interest in meditation? Through my example and having acquired a taste of meditation, the benefits of meditation had resonated. So, he asked for help.

Given his experience with games and exposure to Gamification, my son loves to “level up” in whatever he does. For those who don’t know, leveling up is achieving a related series of measurable goals and giving that achievement a name. It’s best done as part of a fun or adventurous narrative.

Unless made quite fun, being still and focusing on ones breath for any period of time can be torture for a child. It was time to cook up an appealing solution.

Combining his love of Minecraft, his desire to achieve, and the idea of “leveling up”, I made the following achievement levels for my little player:

  • Level 1 – Bow and Arrow – One understands the initial thoughts about meditation
  • Level 2 – Wooden Sword – Meditated one time
  • Level 3 – Stone Sword – Meditated for any amount of time 3 days in a row
  • Level 4 – Iron Sword – Meditated 5 days in a row. Diamond Sword level requirements were secret and are revealed at this time.
  • Level 5 – Diamond Sword – Number of days in a row required to meditate: 1 + (6 sided dice roll) for a chance to win the diamond sword. (In this case, 5 days since he rolled a 4.)

To get the diamond sword, he rolls a 6 sided dice after 5 days and he has a 1 in 6 chance of winning. If he doesn’t win, he does another 5 days but he will have a 2 / 6 chance of winning. If he doesn’t win, another 5 days go by and he’ll have a 3 / 6 chance of winning and so on.

Figuring out this Diamond Sword level required me to reach out to the wonderful Gamification Hub community for ideas. Which brought up some good questions such as “Is any of this tangible? Is this a Minecraft modification to the game?”

Simply, he does not receive anything tangible. There is no Minecraft game modification created for him. He simply knows what level he is at with respect to meditation. Although getting a sword is all in his mind, he’s quite happy knowing that he has achieved a certain level of recognized status.

Has meditation and this approach helped? Yes, it has helped. No matter where he is, it provides an escape hatch where he can reflect on what’s going on. In the long run, meditation yields a better brain. So, he is experiencing short term wins and also long term gains.

How long will such an approach last? For him, it lasted about two to three months. When someone pointed out that they don’t need levels, he declared he doesn’t need levels either. Yet, yesterday he was concerned that he lost some levels since he hasn’t meditated in awhile. Through future technology such as the Muse headband, I think meditation could be made more real to him. Until then, we can make the intangible tangible through a Mindful Minecraft Meditation.

Castle In Twilight

Authors note: The term “Unofficial” is used here in this post in order to comply with the Mojang brand guidelines.

Easy To Forget The Incredible and Virtual Reality Is Incredible

It’s easy to forget the incredible.

I’m wearing the Oculus Rift. It has been awhile and I wanted to revisit the Tuscany and Titans of Space demos. Although I have played the demos multiple times before, I still get an emotional charge when I play them.

The Tuscany demo made me laugh when a lint / seedling startled me when it floated into view. The fireplace almost made me feel warm. The butterfly made me smile. I felt peace while staring at the fountain.

When comparing our sun with much larger stars, the Titans of Space demo instilled a sense of awe and majesty. As Yakko of the Animaniacs said, “It’s a great big universe and we’re all really puny.”

Watching these scenes and listening to the associated sounds and music, filled me with inspiration and wonder for our future.

What incredible future shall we create?