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

simonpeter
When I try the command to create a pair of migration files I get an error. user=&gt; (create-migration "guestbook") Execution error (Ill...
New
herminiotorres
Hi @Margaret , On page VII the book tells us the example and snippets will be all using Elixir version 1.11 But on page 3 almost the en...
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
alanq
This isn’t directly about the book contents so maybe not the right forum…but in some of the code apps (e.g. turbo/06) it sends a TURBO_ST...
New
cro
I am working on the “Your Turn” for chapter one and building out the restart button talked about on page 27. It recommends looking into ...
New
fynn
This is as much a suggestion as a question, as a note for others. Locally the SGP30 wasn’t available, so I ordered a SGP40. On page 53, ...
New
jskubick
I think I might have found a problem involving SwitchCompat, thumbTint, and trackTint. As entered, the SwitchCompat changes color to hol...
New
tkhobbes
After some hassle, I was able to finally run bin/setup, now I have started the rails server but I get this error message right when I vis...
New
andreheijstek
After running /bin/setup, the first error was: The foreman' command exists in these Ruby versions: That was easy to fix: gem install fore...
New
davetron5000
Hello faithful readers! If you have tried to follow along in the book, you are asked to start up the dev environment via dx/build and ar...
New

Other popular topics Top

ohm
Which, if any, games do you play? On what platform? I just bought (and completed) Minecraft Dungeons for my Nintendo Switch. Other than ...
New
wolf4earth
@AstonJ prompted me to open this topic after I mentioned in the lockdown thread how I started to do a lot more for my fitness. https://f...
New
DevotionGeo
I know that these benchmarks might not be the exact picture of real-world scenario, but still I expect a Rust web framework performing a ...
New
AstonJ
Curious to know which languages and frameworks you’re all thinking about learning next :upside_down_face: Perhaps if there’s enough peop...
New
AstonJ
If you are experiencing Rails console using 100% CPU on your dev machine, then updating your development and test gems might fix the issu...
New
DevotionGeo
The V Programming Language Simple language for building maintainable programs V is already mentioned couple of times in the forum, but I...
New
Margaret
Hello everyone! This thread is to tell you about what authors from The Pragmatic Bookshelf are writing on Medium.
1142 25749 758
New
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: