https://kotlinlang.org logo
Channels
100daysofcode
100daysofkotlin
100daysofkotlin-2021
advent-of-code
aem
ai
alexa
algeria
algolialibraries
amsterdam
android
android-architecture
android-databinding
android-studio
androidgithubprojects
androidthings
androidx
androidx-xprocessing
anime
anko
announcements
apollo-kotlin
appintro
arabic
argentina
arkenv
arksemdevteam
armenia
arrow
arrow-contributors
arrow-meta
ass
atlanta
atm17
atrium
austin
australia
austria
awesome-kotlin
ballast
bangladesh
barcelona
bayarea
bazel
beepiz-libraries
belgium
benchmarks
berlin
big-data
books
boston
brazil
brikk
budapest
build
build-tools
bulgaria
bydgoszcz
cambodia
canada
carrat
carrat-dev
carrat-feed
chicago
chile
china
chucker
cincinnati-user-group
cli
clikt
cloudfoundry
cn
cobalt
code-coverage
codeforces
codemash-precompiler
codereview
codingame
codingconventions
coimbatore
collaborations
colombia
colorado
communities
competitive-programming
competitivecoding
compiler
compose
compose-android
compose-desktop
compose-hiring
compose-ios
compose-mp
compose-ui-showcase
compose-wear
compose-web
confetti
connect-audit-events
corda
cork
coroutines
couchbase
coursera
croatia
cryptography
cscenter-course-2016
cucumber-bdd
cyprus
czech
dagger
data2viz
databinding
datascience
dckotlin
debugging
decompose
decouple
denmark
deprecated
detekt
detekt-hint
dev-core
dfw
docs-revamped
dokka
domain-driven-design
doodle
dsl
dublin
dutch
eap
eclipse
ecuador
edinburgh
education
effective-kotlin
effectivekotlin
emacs
embedded-kotlin
estatik
event21-community-content
events
exposed
failgood
fb-internal-demo
feed
firebase
flow
fluid-libraries
forkhandles
forum
fosdem
fp-in-kotlin
framework-elide
freenode
french
fritz2
fuchsia
functional
funktionale
gamedev
ge-kotlin
general-advice
georgia
geospatial
german-lang
getting-started
github-workflows-kt
glance
godot-kotlin
google-io
gradle
graphic
graphkool
graphql
graphql-kotlin
graviton-browser
greece
grpc
gsoc
gui
hackathons
hacktoberfest
hamburg
hamkrest
helios
helsinki
hexagon
hibernate
hikari-cp
hire-me
hiring
hongkong
hoplite
http4k
hungary
hyderabad
image-processing
india
indonesia
inkremental
intellij
intellij-plugins
intellij-tricks
internships
introduce-yourself
io
ios
iran
israel
istanbulcoders
italian
jackson-kotlin
jadx
japanese
jasync-sql
java-to-kotlin-refactoring
javadevelopers
javafx
javalin
javascript
jdbi
jhipster-kotlin
jobsworldwide
jpa
jshdq
juul-libraries
jvm-ir-backend-feedback
jxadapter
k2-early-adopters
kaal
kafka
kakao
kalasim
kapt
karachi
karg
karlsruhe
kash_shell
kaskade
kbuild
kdbc
kgen-doc-tools
kgraphql
kinta
klaxon
klock
kloudformation
kmdc
kmm-español
kmongo
knbt
knote
koalaql
koans
kobalt
kobweb
kodein
kodex
kohesive
koin
koin-dev
komapper
kondor-json
kong
kontent
kontributors
korau
korean
korge
korim
korio
korlibs
korte
kotest
kotest-contributors
kotless
kotlick
kotlin-asia
kotlin-beam
kotlin-by-example
kotlin-csv
kotlin-data-storage
kotlin-foundation
kotlin-fuel
kotlin-in-action
kotlin-inject
kotlin-latam
kotlin-logging
kotlin-multiplatform-contest
kotlin-mumbai
kotlin-native
kotlin-pakistan
kotlin-plugin
kotlin-pune
kotlin-roadmap
kotlin-samples
kotlin-sap
kotlin-serbia
kotlin-spark
kotlin-szeged
kotlin-website
kotlinacademy
kotlinbot
kotlinconf
kotlindl
kotlinforbeginners
kotlingforbeginners
kotlinlondon
kotlinmad
kotlinprogrammers
kotlinsu
kotlintest
kotlintest-devs
kotlintlv
kotlinultimatechallenge
kotlinx-datetime
kotlinx-files
kotlinx-html
kotrix
kotson
kovenant
kprompt
kraph
krawler
kroto-plus
ksp
ktcc
ktfmt
ktlint
ktor
ktp
kubed
kug-leads
kug-torino
kvision
kweb
lambdaworld_cadiz
lanark
language-evolution
language-proposals
latvia
leakcanary
leedskotlinusergroup
lets-have-fun
libgdx
libkgd
library-development
lincheck
linkeddata
lithuania
london
losangeles
lottie
love
lychee
macedonia
machinelearningbawas
madrid
malaysia
mathematics
meetkotlin
memes
meta
metro-detroit
mexico
miami
micronaut
minnesota
minutest
mirror
mockk
moko
moldova
monsterpuzzle
montreal
moonbean
morocco
motionlayout
mpapt
mu
multiplatform
mumbai
munich
mvikotlin
mvrx
myndocs-oauth2-server
naming
navigation-architecture-component
nepal
new-mexico
new-zealand
newname
nigeria
nodejs
norway
npm-publish
nyc
oceania
ohio-kotlin-users
oldenburg
oolong
opensource
orbit-mvi
osgi
otpisani
package-search
pakistan
panamá
pattern-matching
pbandk
pdx
peru
philippines
phoenix
pinoy
pocketgitclient
polish
popkorn
portugal
practical-functional-programming
proguard
prozis-android-backup
pyhsikal
python
python-contributors
quasar
random
re
react
reaktive
realm
realworldkotlin
reductor
reduks
redux
redux-kotlin
refactoring-to-kotlin
reflect
refreshversions
reports
result
rethink
revolver
rhein-main
rocksdb
romania
room
rpi-pico
rsocket
russian
russian_feed
russian-kotlinasfirst
rx
rxjava
san-diego
science
scotland
scrcast
scrimage
script
scripting
seattle
serialization
server
sg-user-group
singapore
skia-wasm-interop-temp
skrape-it
slovak
snake
sofl-user-group
southafrica
spacemacs
spain
spanish
speaking
spek
spin
splitties
spotify-mobius
spring
spring-security
squarelibraries
stackoverflow
stacks
stayhungrystayfoolish
stdlib
stlouis
strife-discord-lib
strikt
students
stuttgart
sudan
swagger-gradle-codegen
swarm
sweden
swing
swiss-user-group
switzerland
talking-kotlin
tallinn
tampa
teamcity
tegal
tempe
tensorflow
terminal
test
testing
testtestest
texas
tgbotapi
thailand
tornadofx
touchlab-tools
training
tricity-kotlin-user-group
trójmiasto
truth
tunisia
turkey
turkiye
twitter-feed
uae
udacityindia
uk
ukrainian
uniflow
unkonf
uruguay
utah
uuid
vancouver
vankotlin
vertx
videos
vienna
vietnam
vim
vkug
vuejs
web-mpp
webassembly
webrtc
wimix_sentry
wwdc
zircon
Powered by
Title
a

Aaron Yoder

11/11/2021, 1:15 AM
I'm a little confused. I want to use a boolean value from my model to show/hide some things on my UI, but it doesn't work if I have a TextField in my set of composables. The state won't change for any of the composables in the block
In psuedocode:
if(model.shouldShow()) { // Doesn't show/hide
 Text("Title")
 TextField(...)
 Button(...)
}


Text("Title")
TextField(...)
if(model.shouldShow()) { // Does show/hide
 Button(...)
}
Actually, I guess I'm misunderstanding something. If there's something that triggers the TextField to update, then it will work, but otherwise it doesn't. I do understand that the boolean needs to be observable for the UI state to change, but I'm passing the boolean from a function, which is checking whether a list has > 0 items, and I'm not sure how I would make that observable.
t

Tobias Suchalla

11/11/2021, 6:47 AM
Maybe with
derivedStateOf
(if your list is an observable state):
val shouldShow by derivedStateOf { list.size > 0 }
z

Zach Klippenstein (he/him) [MOD]

11/11/2021, 2:49 PM
Your list needs to either be an immutable list in a MutableState, or a SnapshotStateList/mutableStateListOf
You don't need to use derivedState just to propagate change notifications, although it will save unnecessary recompositions once the list is non-empty.
a

Aaron Yoder

11/11/2021, 5:00 PM
@Zach Klippenstein (he/him) [MOD] I've provided a more concrete example with two classes here: https://gist.github.com/aaronjyoder/5443f0da5765c1892fcbb199ff415737 and https://gist.github.com/aaronjyoder/c10c214f8c816fea28ba23fe6658b862
Those gists reflect the state of the code without the mentioned modifications above. I have tried derivedStateOf and tried using MutableState, though I don't see any changes to how things function by doing that.
z

Zach Klippenstein (he/him) [MOD]

11/11/2021, 5:02 PM
can you share your code after making the changes?
a

Aaron Yoder

11/11/2021, 5:02 PM
Sure
I assume nothing needs to change in the other gist; I have other areas of my code where I've used mutableStateOf without issue so that's why I'm a little confused here; those other areas of code don't deal with lists/sets in this way though
z

Zach Klippenstein (he/him) [MOD]

11/11/2021, 5:06 PM
You missed a word in my original suggestion: the lists need to be immutable if they’re in a
MutableState
MutableState
only sends change notifications when its reference changes, so if you’re mutating the same list then no change notifications get sent
a

Aaron Yoder

11/11/2021, 5:06 PM
Oh, so if I use that, I have to instantiate a new set every time its contents change?
z

Zach Klippenstein (he/him) [MOD]

11/11/2021, 5:08 PM
Yes, or use a
mutableStateMapOf
if you don’t want to do that
a

Aaron Yoder

11/11/2021, 5:10 PM
Are there any other alternatives? This would require me to change quite a lot since I am constantly altering the contents of those sets
z

Zach Klippenstein (he/him) [MOD]

11/11/2021, 5:11 PM
Not really. You either have to make the property itself a mutable state (or
StateFlow
, or
BehaviorSubject
, or etc) with an immutable collection, or use a collection type that is aware of the snapshot state system.
a

Aaron Yoder

11/11/2021, 5:12 PM
Alright thanks
z

Zach Klippenstein (he/him) [MOD]

11/11/2021, 5:12 PM
It’s easy to treat a map like a set, just use
Unit
as the value type
👍 1
a

Aaron Yoder

11/12/2021, 4:50 PM
Just in case anyone else comes across this: perhaps this isn't the cleanest way of doing it, but I decided to use a boolean with
mutableStateOf
and observe that, and change the state of the boolean upon selection/deselection since that was the goal anyway (to make UI appear or disappear based on whether something is selected or not).