dachristenson

dachristenson

Kotlin and Android Development featuring Jetpack: Transformations class doesn't seem to exist anymore (pp. 140-141

@mfazio23

Android Studio will not accept anything I do when trying to use the Transformations class, as described on pp. 140-141. Googling around reveals that ANOTHER change has been made, and that Transformations no long exists as such but is now built-into Kotlin in some way. I found an example about how to change Transformations.mapswitch() to someClass.mapswitch() but no complete example about how to do the same with Transformations.map(). My efforts to apply the same format to all of the Transformations.map() statements just changed the error from “Unresolved reference: Transformations” to “Type mismatch. Required: Player. Found: Player?”, for instance. This despite setting “lc_version” to “2.3.0”.

What should I do to get Chapter 5’s code working?

Thanks in advance!

Marked As Solved

mfazio23

mfazio23

Author of Kotlin and Android Development featuring Jetpack

tl;dr: Change to calling map { ... } on the LiveData object, change the variable to its nullable version.

It seems like you are on the right track with how you tried to fix this. With v2.6.0 of the Lifecycle library, the Transformations was completely removed (which you unfortunately had to find out the hard way), but thankfully the code is simpler now.

For a concrete example, this code:

this.currentPlayer = Transformations.map(this.currentGame) { gameWithPlayers ->
    gameWithPlayers?.players?.firstOrNull { it.isRolling }
}

is now

this.currentPlayer = this.currentGame.map { gameWithPlayers ->
    gameWithPlayers?.players?.firstOrNull { it.isRolling }
}

But, as you discovered, this causes issues with nullability due to how newer versions of LiveData handle null values. Luckily, this is an easy enough fix; change the LiveData variable to have a nullable type inside of it.
Specifically, this means:

val currentPlayer: LiveData<Player>

becomes

val currentPlayer: LiveData<Player?>

That should resolve the issues you have, let you move forward, and get rid of the Transformations class which was never my favorite in the first place!

Where Next?

Popular Pragmatic Bookshelf topics Top

abtin
page 20: … protoc command… I had to additionally run the following go get commands in order to be able to compile protobuf code using go...
New
belgoros
Following the steps described in Chapter 6 of the book, I’m stuck with running the migration as described on page 84: bundle exec sequel...
New
jeffmcompsci
Title: Design and Build Great Web APIs - typo “https://company-atk.herokuapp.com/2258ie4t68jv” (page 19, third bullet in URL list) Typo:...
New
mikecargal
Title: Hands-On Rust (Chapter 11: prefab) Just played a couple of amulet-less games. With a bit of debugging, I believe that your can_p...
New
conradwt
First, the code resources: Page 237: rumbl_umbrella/apps/rumbl/mix.exs Note: That this file is missing. Page 238: rumbl_umbrella/app...
New
gilesdotcodes
In case this helps anyone, I’ve had issues setting up the rails source code. Here were the solutions: In Gemfile, change gem 'rails' t...
New
curtosis
Running mix deps.get in the sensor_hub directory fails with the following error: ** (Mix) No SSH public keys found in ~/.ssh. An ssh aut...
New
akraut
The markup used to display the uploaded image results in a Phoenix.LiveView.HTMLTokenizer.ParseError error. lib/pento_web/live/product_l...
New
s2k
Hi all, currently I wonder how the Tailwind colours work (or don’t work). For example, in app/views/layouts/application.html.erb I have...
New
New

Other popular topics Top

New
AstonJ
Just done a fresh install of macOS Big Sur and on installing Erlang I am getting: asdf install erlang 23.1.2 Configure failed. checking ...
New
AstonJ
I ended up cancelling my Moonlander order as I think it’s just going to be a bit too bulky for me. I think the Planck and the Preonic (o...
New
AstonJ
Continuing the discussion from Thinking about learning Crystal, let’s discuss - I was wondering which languages don’t GC - maybe we can c...
New
AstonJ
Saw this on TikTok of all places! :lol: Anyone heard of them before? Lite:
New
AstonJ
We’ve talked about his book briefly here but it is quickly becoming obsolete - so he’s decided to create a series of 7 podcasts, the firs...
New
AstonJ
Was just curious to see if any were around, found this one: I got 51/100: Not sure if it was meant to buy I am sure at times the b...
New
husaindevelop
Inside our android webview app, we are trying to paste the copied content from another app eg (notes) using navigator.clipboard.readtext ...
New
New
CommunityNews
A Brief Review of the Minisforum V3 AMD Tablet. Update: I have created an awesome-minisforum-v3 GitHub repository to list information fo...
New

Sub Categories: