(#) Frequently changing state should not be directly read in composable function !!! WARNING: Frequently changing state should not be directly read in composable function This is a warning. Id : `FrequentlyChangedStateReadInComposition` Summary : Frequently changing state should not be directly read in composable function Severity : Warning Category : Performance Platform : Any Vendor : Jetpack Compose Identifier : androidx.compose.foundation Feedback : https://issuetracker.google.com/issues/new?component=612128 Min : Lint 8.0 and 8.1 Compiled : Lint 8.7+ Artifact : [androidx.compose.foundation:foundation-android](androidx_compose_foundation_foundation-android.md.html) Since : 1.5.0 Affects : Kotlin and Java files and test sources Editing : This check runs on the fly in the IDE editor Implementation : [Source Code](https://cs.android.com/androidx/platform/frameworks/support/+/androidx-main:/compose/foundation/foundation-lint/src/main/java/androidx/compose/foundation/lint/LazyLayoutStateReadInCompositionDetector.kt) Tests : [Source Code](https://cs.android.com/androidx/platform/frameworks/support/+/androidx-main:/compose/foundation/foundation-lint/src/test/java/androidx/compose/foundation/lint/LazyLayoutStateReadInCompositionDetectorTest.kt) Copyright Year : 2022 This property is observable and is updated after every scroll or remeasure. If you use it in the composable function directly, it will be recomposed on every change, causing potential performance issues including infinity recomposition loops. Prefer wrapping it with derivedStateOf to use calculation based on this property in composition or collect changes inside LaunchedEffect instead. !!! Tip This lint check has an associated quickfix available in the IDE. (##) Example Here is an example of lint warnings produced by this check: ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~text src/androidx/compose/foundation/foo/test.kt:10:Warning: Frequently changing state should not be directly read in composable function [FrequentlyChangedStateReadInComposition] val index = state.firstVisibleItemIndex --------------------------- src/androidx/compose/foundation/foo/test.kt:11:Warning: Frequently changing state should not be directly read in composable function [FrequentlyChangedStateReadInComposition] val offset = state.firstVisibleItemScrollOffset ---------------------------------- src/androidx/compose/foundation/foo/test.kt:12:Warning: Frequently changing state should not be directly read in composable function [FrequentlyChangedStateReadInComposition] val layoutInfo = state.layoutInfo ---------------- src/androidx/compose/foundation/foo/test.kt:17:Warning: Frequently changing state should not be directly read in composable function [FrequentlyChangedStateReadInComposition] val index = state.firstVisibleItemIndex --------------------------- src/androidx/compose/foundation/foo/test.kt:18:Warning: Frequently changing state should not be directly read in composable function [FrequentlyChangedStateReadInComposition] val offset = state.firstVisibleItemScrollOffset ---------------------------------- src/androidx/compose/foundation/foo/test.kt:19:Warning: Frequently changing state should not be directly read in composable function [FrequentlyChangedStateReadInComposition] val layoutInfo = state.layoutInfo ---------------- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Here is the source file referenced above: `src/androidx/compose/foundation/foo/test.kt`: ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~kotlin linenumbers package androidx.compose.foundation.foo import androidx.compose.runtime.Composable import androidx.compose.foundation.lazy.grid.LazyGridState import androidx.compose.foundation.lazy.LazyListState @Composable fun TestGrid(state: LazyGridState) { val index = state.firstVisibleItemIndex val offset = state.firstVisibleItemScrollOffset val layoutInfo = state.layoutInfo } @Composable fun TestList(state: LazyListState) { val index = state.firstVisibleItemIndex val offset = state.firstVisibleItemScrollOffset val layoutInfo = state.layoutInfo } ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ You can also visit the [source code](https://cs.android.com/androidx/platform/frameworks/support/+/androidx-main:/compose/foundation/foundation-lint/src/test/java/androidx/compose/foundation/lint/LazyLayoutStateReadInCompositionDetectorTest.kt) for the unit tests for this check to see additional scenarios. The above example was automatically extracted from the first unit test found for this lint check, `LazyLayoutStateReadInCompositionDetector.observablePropertiesUsedInComposableFunction`. To report a problem with this extracted sample, visit https://issuetracker.google.com/issues/new?component=612128. (##) Including !!! This is not a built-in check. To include it, add the below dependency to your project. ``` // build.gradle.kts implementation("androidx.compose.foundation:foundation-android:1.8.0-alpha07") // build.gradle implementation 'androidx.compose.foundation:foundation-android:1.8.0-alpha07' // build.gradle.kts with version catalogs: implementation(libs.foundation.android) # libs.versions.toml [versions] foundation-android = "1.8.0-alpha07" [libraries] # For clarity and text wrapping purposes the following declaration is # shown split up across lines, but in TOML it needs to be on a single # line (see https://github.com/toml-lang/toml/issues/516) so adjust # when pasting into libs.versions.toml: foundation-android = { module = "androidx.compose.foundation:foundation-android", version.ref = "foundation-android" } ``` 1.8.0-alpha07 is the version this documentation was generated from; there may be newer versions available. NOTE: These lint checks are **also** made available separate from the main library. You can also use `androidx.compose.foundation:foundation-lint:1.8.0-alpha07`. [Additional details about androidx.compose.foundation:foundation-android](androidx_compose_foundation_foundation-android.md.html). (##) Suppressing You can suppress false positives using one of the following mechanisms: * Using a suppression annotation like this on the enclosing element: ```kt // Kotlin @Suppress("FrequentlyChangedStateReadInComposition") fun method() { problematicStatement() } ``` or ```java // Java @SuppressWarnings("FrequentlyChangedStateReadInComposition") void method() { problematicStatement(); } ``` * Using a suppression comment like this on the line above: ```kt //noinspection FrequentlyChangedStateReadInComposition problematicStatement() ``` * Using a special `lint.xml` file in the source tree which turns off the check in that folder and any sub folder. A simple file might look like this: ```xml <?xml version="1.0" encoding="UTF-8"?> <lint> <issue id="FrequentlyChangedStateReadInComposition" severity="ignore" /> </lint> ``` Instead of `ignore` you can also change the severity here, for example from `error` to `warning`. You can find additional documentation on how to filter issues by path, regular expression and so on [here](https://googlesamples.github.io/android-custom-lint-rules/usage/lintxml.md.html). * In Gradle projects, using the DSL syntax to configure lint. For example, you can use something like ```gradle lintOptions { disable 'FrequentlyChangedStateReadInComposition' } ``` In Android projects this should be nested inside an `android { }` block. * For manual invocations of `lint`, using the `--ignore` flag: ``` $ lint --ignore FrequentlyChangedStateReadInComposition ...` ``` * Last, but not least, using baselines, as discussed [here](https://googlesamples.github.io/android-custom-lint-rules/usage/baselines.md.html).