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Debugging Jetpack Compose Kimin Ryu, Senior Developer, HOLIX

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Agenda • Jetpack Compose Debugging Tools • Debugging Practice • Debugging Mindset • Common Issues • recomposition • jank • tracing • Tips • Summary

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Jetpack Compose Debugging Tools Compose ѐߊ द ࢎਊೞח ٣ߡӦ بҳٜ

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1. Layout Inspector ઱۽ ޙઁܳ ੋ૑ ೞחؘ ࢎਊ • Recomposition Count • Recomposition Skip Count • Recomposition Highlight * Android Studio Hedgehogࠗఠ э਷ చীࢲ Device ചݶҗ Layout Inspectorܳ ೣԋ ࢎਊೡ ࣻ ੓਺ (Embedded Layout Inspector)

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“৵ ੉ composableীࢲ recomposition੉ ੌযզө?”

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Types of recomposition Unskippable recomposition Indirect recomposition A parent composable got recomposed and this caused parameters to change Direct recomposition A compose state object inside the composable changed.

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@Composable fun DirectRecomposition() { var count by remember { mutableStateOf(0) } Text("$count") Button(onClick = { count++ }) { Text("Increment") } }

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@Composable fun IndirectRecomposition() { var count by remember { mutableStateOf(0) } val doubled = count * 2 MyText(doubled) Button(onClick = { count++ }) { Text("Increment") } } @Composable fun MyText(count: Int) { Text("$count") }

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@Composable fun UnstableRecomposition() { var count by remember { mutableStateOf(0) } Text("$count") var list by remember { mutableStateOf(listOf(1, 2, 3)) } MyList(list) Button(onClick = { count++ }) { Text("Increment") } } @Composable fun MyList(list: List) { /**/ }

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Problem: Composableীࢲ যڃ ч ٸޙী recomposition੉ ੌযաח૑ ঌ ࣻ হ਺

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2. Recomposition state in debugger🎉

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Recomposition state • Unchanged - ߸҃੉ হ਺ • Changed - ߸҃੉ ੌযթ • Uncertain • Static - ߸҃੉ হਸ Ѫ੉ۄ ౸ױؽ • Unstable

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@Composable fun IndirectRecomposition() { var count by remember { mutableStateOf(0) } val doubled = count * 2 MyText(doubled) Button(onClick = { count++ }) { Text("Increment") } } @Composable fun MyText(count: Int) { Text("$count") }

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@Composable fun UnstableRecomposition() { var count by remember { mutableStateOf(0) } Text("$count") var list by remember { mutableStateOf(listOf(1, 2, 3)) } MyList(list) Button(onClick = { count++ }) { Text("Increment") } } @Composable fun MyList(list: List) { /**/ }

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3. Logs ੣਷ Recomposition੉ ߊࢤೞח ࢚ടীࢲ જ਷ ؀উ झ௼܀੉ա গפݫ੉࣌੉ ੌযզ ٸ ч੉ ࡅܰѱ ߸ೞݴ recomposeغחؘ, breakpointܳ ੟ই ݒ ೐ۨ੐݃׮ чਸ ࠁח Ѫ਷ য۰਑

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@Composable fun ScrollingList() { val scrollState = rememberLazyListState() var count by remember { mutableStateOf(0) } Log.d("ScrollingList", "${scrollState.firstVisibleItemIndex}") Button(onClick = { count++ }) { Text(text = "Increment") } Text(text = "count: $count") LazyColumn( modifier = Modifier.fillMaxSize(), state = scrollState, ) { items(100) { Text(text = "index $it") } } }

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@Composable fun ScrollingList() { val scrollState = rememberLazyListState() var count by remember { mutableStateOf(0) } Log.d("ScrollingList", "${scrollState.firstVisibleItemIndex}") Button(onClick = { count++ }) { Text(text = "Increment") } Text(text = "count: $count") LazyColumn( modifier = Modifier.fillMaxSize(), state = scrollState, ) { items(100) { Text(text = "index $it") } } }

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@Composable fun ScrollingList() { val scrollState = rememberLazyListState() var count by remember { mutableStateOf(0) } SideEffect { Log.d("ScrollingList", "${scrollState.firstVisibleItemIndex}") } Button(onClick = { count++ }) { Text(text = "Increment") } Text(text = "count: $count") LazyColumn( modifier = Modifier.fillMaxSize(), state = scrollState, ) { items(100) { Text(text = "index $it") } } }

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4. Visual Lint 22֙ I/Oীࢲ ୭ୡ ҕѐ ׼दী View दझమ݅ ੸ਊ. Android Studio Hedgehogীࢲ Compose Previewী ؀ೠ ૑ਗ द੘🎉

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5. Tracing (Profiler) System trace ծ਷ overhead दр ஏ੿੉ ਊ੉ೣ ݃ఊػ ੉߮౟݅ਸ ୶੸ Method trace ֫਷ overhead ݽٚ method callਸ ࠁৈષ

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“System trace੄ ࡅܲ ࣘب৬ Method trace੄ ੿ࠁܳ о઎ਵݶ…”

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// build.gradle dependencies { implementation(“androidx.compose.runtime:runtime-tracing:") }

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6. Macrobenchmark ইې৬ э਷ য೒ܻா੉࣌ ز੘੄ ࢿמਸ ஏ੿ೡ ࣻ ੓਺ • App startup • Scroll • Animation

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Debugging Practice ٣ߡӦ ೐۽ࣁझ ୓೷ ೧ࠁӝ

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Debugging Mindset A process for debugging

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Define Reproduce Validate Assumptions Fix

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٣ߡӦ਷ ޙઁо ޖ঺ੋ૑ ੿੄ೞח Ѫীࢲ द੘ • যڌѱ ز੘ೞח Ѫ੉ۄ ৘࢚೮ա? • ؀न যڃ ੌ੉ ੌযաҊ ੓ա? • ৵ Ӓۧѱ ز੘ೡ Ѫ੉ۄ ࢤп೮ա? • ׼नҗ زܐٜ਷ যڃ о੿ਸ ೞҊ ੓ա? Define Reproduce Validate Assumptions Fix What is the problem?

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੤അ оמೠ ৘दܳ ҳഅ • ৘࢚чҗ पઁч, ഑਷ ৘࢚ ز੘җ पઁ ز੘ਸ ࠺Үೞח పझ౟ ੘ࢿ • (TIP) ੘਷ playground ೐۽ં౟ ഑਷ ݽٕਸ ٜ݅যفݶ ಞೞ׮. Define Reproduce Validate Assumptions Fix Reproduce the problem

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ޙઁܳ ੤അೡ ࣻ ੓ਵפ بҳܳ ੉ਊೞৈ оࢸਸ Ѩૐ • ޙઁী ٮۄ ب਑ਸ ߉ਸ ࣻ ੓ח ׮নೠ بҳٜ੉ ੓਺ Define Reproduce Validate Assumptions Fix Validate Assumptions

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ޙઁܳ ೧Ѿ🎉 • పझ౟ܳ ా೧ ޙઁо ೧Ѿغ঻ח૑ ഛੋ Define Reproduce Validate Assumptions Fix Implement the fix

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Debugging Case #1 Recomposition Layout Inspector۽ recompositionਸ ನ଱ೞҊ, recomposition stateܳ ഛੋ೧ ޙઁ ೧Ѿ੄ द੘੼ ଺ӝ

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lastEpisodeDate is unstable!

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FollowedPodcastCarouselItem( … lastEpisodeDate = lastEpisodeDate, … ) @Composable private fun FollowedPodcastCarouselItem( … lastEpisodeDate: OffsetDateTime? = null, … ) { … if (lastEpisodeDate != null) { Text( text = lastEpisodeDate?.let { lastUpdated(it) }, … ) } … }

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FollowedPodcastCarouselItem( … lastEpisodeDateText = lastEpisodeDate?.let { lastUpdated(it) }, … ) @Composable private fun FollowedPodcastCarouselItem( … lastEpisodeDateText: String? = null, … ) { … if (lastEpisodeDateText != null) { Text( text = lastEpisodeDateText, … ) } … }

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Debugging Case #2 Jank Scroll, Animation١ীࢲ ߡߢ੐੉ ߊࢤ೮ਸ ٸ, ޙઁܳ ೧ѾೞҊ MacroBenchmark۽ ѐࢶ ഛੋೞӝ

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@Google I/O 23

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Debugging Case #3 Tracing दрਸ য়ې ੟ইݡח Composable੉ ੓ח Ѫ э׮? Profiler - System traceܳ ੉ਊ

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x

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class BigObject { init { List(250000) { it } } }

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class BigObject { init { trace("Big Object") { List(250000) { it } } } }

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val expensive = remember { BigObject() }

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fun ProvideAndroidCompositionLocals( owner: AndroidComposeView, content: @Composable () -> Unit ) { val view = owner val context = view.context …… val uriHandler = remember { AndroidUriHandler(context) } val saveableStateRegistry = remember { DisposableSaveableStateRegistry(view, viewTreeOwners.savedStateRegistryOwner) } …… val imageVectorCache = obtainImageVectorCache(context, configuration) }

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Tip: Twitter Jetpack Compose rule Jetpack Composeীࢲ पࣻೞѢա ֬஖ӝ ए਍ ࠗ࠙ਸ ੟ই઱ח ktlint rules

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Tip: Compose Compiler Reports Unstable class৬ parameterܳ ޷ܻ ଺ח ߨ

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Setup // build.gradle (root) subprojects { tasks.withType().configureEach { compilerOptions { if (project.findProperty("composeCompilerReports") == "true") { freeCompilerArgs.addAll( "-P", "plugin:androidx.compose.compiler.plugins.kotlin:reportsDestination=" + project.buildDir.absolutePath + “/compose_compiler”, ) } if (project.findProperty("composeCompilerMetrics") == "true") { freeCompilerArgs.addAll( "-P", "plugin:androidx.compose.compiler.plugins.kotlin:metricsDestination=" + project.buildDir.absolutePath + “/compose_compiler” ) } } } }

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Build # 1. local.properties, gradle.properties ١ীࢲ property ࢸ੿ composeCompilerReports=true composeCompilerMetrics=true # 2. terminalীࢲ gradle task प೯ द property ࢸ੿ ➜ ./gradlew -PcomposeCompilerReports=true -PcomposeCompilerMetrics=true assembleDebug

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Result

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Top Level Metrics (-module.json) { "skippableComposables": 16, "restartableComposables": 20, "readonlyComposables": 0, "totalComposables": 20, "restartGroups": 20, "totalGroups": 20, "staticArguments": 21, "certainArguments": 1, "knownStableArguments": 276, "knownUnstableArguments": 1, "unknownStableArguments": 0, "totalArguments": 277, "markedStableClasses": 0, "inferredStableClasses": 3, "inferredUnstableClasses": 2, "inferredUncertainClasses": 0, "effectivelyStableClasses": 3, "totalClasses": 5, "memoizedLambdas": 15, "singletonLambdas": 1, "singletonComposableLambdas": 9, "composableLambdas": 9, "totalLambdas": 15 }

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Top Level Metrics (-module.json) { "skippableComposables": 16, "restartableComposables": 20, “knownUnstableArguments": 1, }

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Composable Signatures (-composables.txt) restartable skippable scheme("[androidx.compose.ui.UiComposable]") fun Greeting( stable name: String stable modifier: Modifier? = @static Companion ) restartable skippable scheme("[androidx.compose.ui.UiComposable]") fun GreetingPreview() restartable skippable scheme("[androidx.compose.ui.UiComposable]") fun DirectRecomposition() restartable skippable scheme("[androidx.compose.ui.UiComposable]") fun IndirectRecomposition() restartable skippable scheme("[androidx.compose.ui.UiComposable]") fun MyText( stable count: Int ) restartable skippable scheme("[androidx.compose.ui.UiComposable]") fun ScrollingList() restartable skippable scheme("[androidx.compose.ui.UiComposable]") fun UnstableRecomposition() restartable scheme("[androidx.compose.ui.UiComposable]") fun MyList( unstable list: List )

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Composable Signatures (-composables.txt) restartable scheme("[androidx.compose.ui.UiComposable]") fun MyList( unstable list: List )

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Composable Table (-composables.csv) package,name,composable,skippable,restartable,readonly,inline,isLambda,hasDefaults,defau ltsGroup,groups,calls, com.example.sample.Greeting,Greeting,1,1,1,0,0,0,0,0,1,1, com.example.sample.GreetingPreview,GreetingPreview,1,1,1,0,0,0,0,0,1,1, com.example.sample.DirectRecomposition,DirectRecomposition,1,1,1,0,0,0,0,0,1,4, com.example.sample.IndirectRecomposition,IndirectRecomposition,1,1,1,0,0,0,0,0,1,4, com.example.sample.MyText,MyText,1,1,1,0,0,0,0,0,1,1, com.example.sample.ScrollingList,ScrollingList,1,1,1,0,0,0,0,0,1,8, com.example.sample.UnstableRecomposition,UnstableRecomposition,1,1,1,0,0,0,0,0,1,1, com.example.sample.MyList,MyList,1,0,1,0,0,0,0,0,1,1,

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classes.txt data class StableClass( val stableProperty1: String, val stableProperty2: Int, val stableProperty3: Long, val stableProperty4: Double ) data class StableNestedClass( val stableClass: StableClass ) data class UnstableClass( val stableProperty1: String, val stableProperty2: Int, val stableProperty3: Long, val unstableProperty1: List, // Date, Map, Set... ) data class UnstableNestedClass( val unstableClass: UnstableClass ) stable class StableClass { stable val stableProperty1: String stable val stableProperty2: Int stable val stableProperty3: Long stable val stableProperty4: Double = Stable } stable class StableNestedClass { stable val stableClass: StableClass = Stable } unstable class UnstableClass { stable val stableProperty1: String stable val stableProperty2: Int stable val stableProperty3: Long unstable val unstableProperty1: List = Unstable } unstable class UnstableNestedClass { unstable val unstableClass: UnstableClass = Unstable }

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⚠ ݣ౭ ݽٕਸ ॳҊ ҅द׮ݶ? ݣ౭ ݽٕ ೐۽ં౟ীࢲ domainҗ э਷ ࣽࣻ kotlin module੄ ௿ېझח 
 Compose compilerо unstable۽ р઱ 3rd party ۄ੉࠳۞ܻܳ ࢎਊೡ ٸب ਬ੄೧ঠ… 1. Compose runtime dependencyܳ ୶оೞѢա 2. UI moduleীࢲ ui model۽ mapping ژח wrapper۽ ੜ хऱࢲ ࢎਊ

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ݽٚ Composable਷ Skippable੉যঠ? ইפ׮. skippable۽ ݅٘ח ࣻҊо प૕੸ੋ о஖ࠁ׮ ੸਷ ҃਋ ޖद • ੗઱ recomposeо غ૑ ঋח composable (৘: ചݶ ױਤ) • ױࣽ൤ ղࠗীࢲ skippableೠ composableਸ о૑Ҋ ੓ח ҃਋

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Compose Compiler Report to HTML

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Mendable

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Summary

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1. ޙઁ ߊࢤ ߑ૑ೞӝ • Lint۽ ੜޅػ ز੘ਸ ঠӝೞח ௏٘ܳ ੘ࢿೞ૑ ঋب۾ ೞ੗ • Twitter compose rules • Visual Lint • Compose Compiler Reportsܳ ా೧ ਫ਼੤੸ਵ۽ ޙઁо ੓ח class, composableਸ ଺੗.

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ز੘ী ޙઁо ੓ਸ ٸ ؀୊ߨ • Layout Inspectorܳ ా೧ ࠛ೙ਃೠ recompositionਸ ଺ইࠁ੗. • Composable functionী breakpointܳ Ѧয ٣ߡѢীࢲ Recomposition Stateܳ ഛੋೡ ࣻ ੓׮. • झ௼܀, গפݫ੉࣌ ١ ࠼بо ੣਷ recomposition੉ ߊࢤೡ ٸח Logܳ ࢎਊೞ੗.

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୭੸ച • composable tracingਸ ా೧ Composableীࢲ য়ې Ѧܻח ࠗ࠙ਸ ఐ૑ೞӝ • Macrobenchmarkܳ ా೧ ࢿמ ೱ࢚ ഛੋ

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Resources • https://goo.gle/jetcaster-pager • https://goo.gle/compose-stability-explained • https://goo.gle/baseline-profiles • https://goo.gle/compose-tracing • https://medium.com/androiddevelopers/jetpack-compose-debugging-recomposition-bfcf4a6f8d37 • https://medium.com/androiddevelopers/jetpack-compose-composition-tracing-9ec2b3aea535 • https://youtube.com/watch?v=Kp-aiSU8qCU

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Q&A Q. Composable ௏٘ ܻ࠭ ౲੉ ੓ਸөਃ? A. ୊਺ী ٣੗ੋ दझమਸ উ੟Ҋ ௏٘ܳ ૢ ٸח ઺ࠂغח ஹನք౟ب ݆Ҋ modifierо ؋૑؋૑ ׳ܻחѱ ࠁӝب উજওणפ׮. ஹನ੷࠶ ௏٘о ݠ݁ࣘীࢲ ੜ উӒ۰૑ח ҃਋о ݆ওחؘ ٣੗ੋ दझమ ҳഅਸ ೞݶࢲ оةࢿ੉ ѐ ࢶغ঻؍ ҃೷੉ ੓णפ׮. ௏٘ ܻ࠭ ౲਷ ইק Ѫ э૑݅, ઁ ҃೷ਸ ݈ॹܻ٘੗ݶ ҳഅ ࢎ೦ਸ যڌѱ ҳഅೡ૑ ҳ࢚ਸ alignೞח োणਸ ૓೯೮ णפ׮. Composeח ࢜۽਍ ӝࣿ੉׮ࠁפ п੗ ѐੋٜ੄ ࣼ۲ب৬ ૑ध Ѻରо ߥয૕ ࣻ ੓חؘ, ੷ח ಕয ೐۽Ӓ ې߁, VOD, ࢎղ ࣁ޷աܳ ా೧ ࢜۽਍ ૑धਸ ੹౵೮णפ׮. ੉۠ җ੿ਸ ా೧ ௏٘ ܻ࠭ ੉੹ী ࢎҊߑधਸ ੌ஖द ெ ௏٘ ܻ࠭ ബਯਸ ֫ੌ ࣻ ੓঻णפ׮.

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Q&A Q. Compose internals ъ੄? ଼?ਸ ࠁݶ Compose Compilerо ঌইࢲ ೧઻ࢲ @Stable, @Immutable annotationਸ ׮ח Ѫਸ ௼ѱ न҃ ॳ૑ ঋইب ػ׮Ҋ غয੓חؘ যڌѱ ࢤпೞदաਃ? (૕ޙ ӝরաח؀۽ ੸যࠌ חؘ ݏѷભ…?) A. Ӓ ޙ੢ ੹റ۽ যڃ ղਊ੉ ੓ח૑ ઁо ੍যࠁ૑ ঋইࢲ ૒੽੸ਵ۽ ׹ਸ ೧ܻ٘ӟ য۰਎ Ѫ эणפ׮. ׮݅, @Stableҗ @Immutable੄ ৉ೡҗ ӝמਸ ੿ഛ൤ ইन׮ݶ ੷ח ԙ ೙ਃೞ׮Ҋ ࢤп೤פ׮. @Stableҗ @Immutable annotation੄ ഝਊ਷ ৉द Compose ղࠗ ௏٘ܳ ଵઑೞदݶ જणפ׮. Color, Dp৬ э਷ Ѫٜ ࠗఠ द੘ೞৈ material, material3١ componentٜী ٜযоח ੋ੗ٜ੄ ҳഅਸ ా೧ annotation੄ ৉ೡਸ ഛੋ ೞप ࣻ ੓ਸ Ѫ эणפ׮. ੷ח ৮੹ ୡӝী ੗ܐо ցޖ ࠗ઒ೞ؍ द੺ ଵҊೡ݅ೠѱ ղࠗ ௏٘ ߆ী হ঻חؘ, ૑Әب stabilityী ؀ೠ ӝળਸ ࣁ਋ח ਬബೠ ೟णߑध੉ۄ ࢤп೤פ׮.

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Thank you