(#) Creating a state object during composition without using `remember` !!! ERROR: Creating a state object during composition without using `remember` This is an error. Id : `UnrememberedMutableState` Summary : Creating a state object during composition without using `remember` Severity : Error Category : Correctness Platform : Any Vendor : Jetpack Compose Identifier : androidx.compose.runtime Feedback : https://issuetracker.google.com/issues/new?component=612128 Min : Lint 8.7+ Compiled : Lint 8.7+ Artifact : [androidx.compose.runtime:runtime-android](androidx_compose_runtime_runtime-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/runtime/runtime-lint/src/main/java/androidx/compose/runtime/lint/UnrememberedStateDetector.kt) Tests : [Source Code](https://cs.android.com/androidx/platform/frameworks/support/+/androidx-main:/compose/runtime/runtime-lint/src/test/java/androidx/compose/runtime/lint/UnrememberedStateDetectorTest.kt) Copyright Year : 2020 State objects created during composition need to be `remember`ed, otherwise they will be recreated during recomposition, and lose their state. Either hoist the state to an object that is not created during composition, or wrap the state in a call to `remember`. (##) Example Here is an example of lint warnings produced by this check: ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~text src/androidx/compose/runtime/foo/{.kt:8:Error: Creating a state object during composition without using remember [UnrememberedMutableState] val foo = mutableStateOf(0) -------------- src/androidx/compose/runtime/foo/{.kt:9:Error: Creating a state object during composition without using remember [UnrememberedMutableState] val bar = mutableStateListOf<Int>() ------------------ src/androidx/compose/runtime/foo/{.kt:10:Error: Creating a state object during composition without using remember [UnrememberedMutableState] val baz = mutableStateMapOf<Int, Float>() ----------------- src/androidx/compose/runtime/foo/{.kt:11:Error: Creating a state object during composition without using remember [UnrememberedMutableState] val derived = derivedStateOf { foo.value } -------------- src/androidx/compose/runtime/foo/{.kt:15:Error: Creating a state object during composition without using remember [UnrememberedMutableState] val foo = mutableStateOf(0) -------------- src/androidx/compose/runtime/foo/{.kt:16:Error: Creating a state object during composition without using remember [UnrememberedMutableState] val bar = mutableStateListOf<Int>() ------------------ src/androidx/compose/runtime/foo/{.kt:17:Error: Creating a state object during composition without using remember [UnrememberedMutableState] val baz = mutableStateMapOf<Int, Float>() ----------------- src/androidx/compose/runtime/foo/{.kt:18:Error: Creating a state object during composition without using remember [UnrememberedMutableState] val derived = derivedStateOf { foo.value } -------------- src/androidx/compose/runtime/foo/{.kt:22:Error: Creating a state object during composition without using remember [UnrememberedMutableState] val foo = mutableStateOf(0) -------------- src/androidx/compose/runtime/foo/{.kt:23:Error: Creating a state object during composition without using remember [UnrememberedMutableState] val bar = mutableStateListOf<Int>() ------------------ src/androidx/compose/runtime/foo/{.kt:24:Error: Creating a state object during composition without using remember [UnrememberedMutableState] val baz = mutableStateMapOf<Int, Float>() ----------------- src/androidx/compose/runtime/foo/{.kt:25:Error: Creating a state object during composition without using remember [UnrememberedMutableState] val derived = derivedStateOf { foo.value } -------------- src/androidx/compose/runtime/foo/{.kt:34:Error: Creating a state object during composition without using remember [UnrememberedMutableState] val foo = mutableStateOf(0) -------------- src/androidx/compose/runtime/foo/{.kt:35:Error: Creating a state object during composition without using remember [UnrememberedMutableState] val bar = mutableStateListOf<Int>() ------------------ src/androidx/compose/runtime/foo/{.kt:36:Error: Creating a state object during composition without using remember [UnrememberedMutableState] val baz = mutableStateMapOf<Int, Float>() ----------------- src/androidx/compose/runtime/foo/{.kt:37:Error: Creating a state object during composition without using remember [UnrememberedMutableState] val derived = derivedStateOf { foo.value } -------------- src/androidx/compose/runtime/foo/{.kt:40:Error: Creating a state object during composition without using remember [UnrememberedMutableState] val foo = mutableStateOf(0) -------------- src/androidx/compose/runtime/foo/{.kt:41:Error: Creating a state object during composition without using remember [UnrememberedMutableState] val bar = mutableStateListOf<Int>() ------------------ src/androidx/compose/runtime/foo/{.kt:42:Error: Creating a state object during composition without using remember [UnrememberedMutableState] val baz = mutableStateMapOf<Int, Float>() ----------------- src/androidx/compose/runtime/foo/{.kt:43:Error: Creating a state object during composition without using remember [UnrememberedMutableState] val derived = derivedStateOf { foo.value } -------------- src/androidx/compose/runtime/foo/{.kt:49:Error: Creating a state object during composition without using remember [UnrememberedMutableState] val foo = mutableStateOf(0) -------------- src/androidx/compose/runtime/foo/{.kt:50:Error: Creating a state object during composition without using remember [UnrememberedMutableState] val bar = mutableStateListOf<Int>() ------------------ src/androidx/compose/runtime/foo/{.kt:51:Error: Creating a state object during composition without using remember [UnrememberedMutableState] val baz = mutableStateMapOf<Int, Float>() ----------------- src/androidx/compose/runtime/foo/{.kt:52:Error: Creating a state object during composition without using remember [UnrememberedMutableState] val derived = derivedStateOf { foo.value } -------------- src/androidx/compose/runtime/foo/{.kt:56:Error: Creating a state object during composition without using remember [UnrememberedMutableState] val foo = mutableStateOf(0) -------------- src/androidx/compose/runtime/foo/{.kt:57:Error: Creating a state object during composition without using remember [UnrememberedMutableState] val bar = mutableStateListOf<Int>() ------------------ src/androidx/compose/runtime/foo/{.kt:58:Error: Creating a state object during composition without using remember [UnrememberedMutableState] val baz = mutableStateMapOf<Int, Float>() ----------------- src/androidx/compose/runtime/foo/{.kt:59:Error: Creating a state object during composition without using remember [UnrememberedMutableState] val derived = derivedStateOf { foo.value } -------------- src/androidx/compose/runtime/foo/{.kt:66:Error: Creating a state object during composition without using remember [UnrememberedMutableState] val foo = mutableStateOf(0) -------------- src/androidx/compose/runtime/foo/{.kt:67:Error: Creating a state object during composition without using remember [UnrememberedMutableState] val bar = mutableStateListOf<Int>() ------------------ src/androidx/compose/runtime/foo/{.kt:68:Error: Creating a state object during composition without using remember [UnrememberedMutableState] val baz = mutableStateMapOf<Int, Float>() ----------------- src/androidx/compose/runtime/foo/{.kt:69:Error: Creating a state object during composition without using remember [UnrememberedMutableState] val derived = derivedStateOf { foo.value } -------------- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Here is the source file referenced above: `src/androidx/compose/runtime/foo/{.kt`: ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~kotlin linenumbers package androidx.compose.runtime.foo import androidx.compose.runtime.* @Composable fun Test() { val foo = mutableStateOf(0) val bar = mutableStateListOf() val baz = mutableStateMapOf() val derived = derivedStateOf { foo.value } } val lambda = @Composable { val foo = mutableStateOf(0) val bar = mutableStateListOf() val baz = mutableStateMapOf() val derived = derivedStateOf { foo.value } } val lambda2: @Composable () -> Unit = { val foo = mutableStateOf(0) val bar = mutableStateListOf() val baz = mutableStateMapOf() val derived = derivedStateOf { foo.value } } @Composable fun LambdaParameter(content: @Composable () -> Unit) {} @Composable fun Test2() { LambdaParameter(content = { val foo = mutableStateOf(0) val bar = mutableStateListOf() val baz = mutableStateMapOf() val derived = derivedStateOf { foo.value } }) LambdaParameter { val foo = mutableStateOf(0) val bar = mutableStateListOf() val baz = mutableStateMapOf() val derived = derivedStateOf { foo.value } } } fun test3() { val localLambda1 = @Composable { val foo = mutableStateOf(0) val bar = mutableStateListOf() val baz = mutableStateMapOf() val derived = derivedStateOf { foo.value } } val localLambda2: @Composable () -> Unit = { val foo = mutableStateOf(0) val bar = mutableStateListOf() val baz = mutableStateMapOf() val derived = derivedStateOf { foo.value } } } @Composable fun Test4() { val localObject = object { val foo = mutableStateOf(0) val bar = mutableStateListOf() val baz = mutableStateMapOf() val derived = derivedStateOf { foo.value } } } ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ You can also visit the [source code](https://cs.android.com/androidx/platform/frameworks/support/+/androidx-main:/compose/runtime/runtime-lint/src/test/java/androidx/compose/runtime/lint/UnrememberedStateDetectorTest.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, `UnrememberedStateDetector.notRemembered`. 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.runtime:runtime-android:1.9.0-alpha01") // build.gradle implementation 'androidx.compose.runtime:runtime-android:1.9.0-alpha01' // build.gradle.kts with version catalogs: implementation(libs.runtime.android) # libs.versions.toml [versions] runtime-android = "1.9.0-alpha01" [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: runtime-android = { module = "androidx.compose.runtime:runtime-android", version.ref = "runtime-android" } ``` 1.9.0-alpha01 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.runtime:runtime-lint:1.9.0-alpha01`. [Additional details about androidx.compose.runtime:runtime-android](androidx_compose_runtime_runtime-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("UnrememberedMutableState") fun method() { problematicStatement() } ``` or ```java // Java @SuppressWarnings("UnrememberedMutableState") void method() { problematicStatement(); } ``` * Using a suppression comment like this on the line above: ```kt //noinspection UnrememberedMutableState 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="UnrememberedMutableState" 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 'UnrememberedMutableState' } ``` In Android projects this should be nested inside an `android { }` block. * For manual invocations of `lint`, using the `--ignore` flag: ``` $ lint --ignore UnrememberedMutableState ...` ``` * Last, but not least, using baselines, as discussed [here](https://googlesamples.github.io/android-custom-lint-rules/usage/baselines.md.html).