(#) Creating a MutableState object with a mutable collection type !!! WARNING: Creating a MutableState object with a mutable collection type This is a warning. Id : `MutableCollectionMutableState` Summary : Creating a MutableState object with a mutable collection type Severity : Warning 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/MutableCollectionMutableStateDetector.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/MutableCollectionMutableStateDetectorTest.kt) Copyright Year : 2021 Writes to mutable collections inside a MutableState will not cause a recomposition - only writes to the MutableState itself will. In most cases you should either use a read-only collection (such as List or Map) and assign a new instance to the MutableState when your data changes, or you can use an snapshot-backed collection such as SnapshotStateList or SnapshotStateMap which will correctly cause a recomposition when their contents are modified. (##) Example Here is an example of lint warnings produced by this check: ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~text src/test/test.kt:12:Warning: Creating a MutableState object with a mutable collection type [MutableCollectionMutableState] val listProperty = mutableStateOf(list) -------------- src/test/test.kt:14:Warning: Creating a MutableState object with a mutable collection type [MutableCollectionMutableState] val setFunction = mutableStateOf(mutableSetOf(1)) -------------- src/test/test.kt:15:Warning: Creating a MutableState object with a mutable collection type [MutableCollectionMutableState] val setProperty = mutableStateOf(set) -------------- src/test/test.kt:17:Warning: Creating a MutableState object with a mutable collection type [MutableCollectionMutableState] val mapFunction = mutableStateOf(mutableMapOf(1 to 1)) -------------- src/test/test.kt:18:Warning: Creating a MutableState object with a mutable collection type [MutableCollectionMutableState] val mapProperty = mutableStateOf(map) -------------- src/test/test.kt:20:Warning: Creating a MutableState object with a mutable collection type [MutableCollectionMutableState] val collectionProperty = mutableStateOf(collection) -------------- src/test/test.kt:28:Warning: Creating a MutableState object with a mutable collection type [MutableCollectionMutableState] val listParameter = mutableStateOf(listParam) -------------- src/test/test.kt:29:Warning: Creating a MutableState object with a mutable collection type [MutableCollectionMutableState] val setParameter = mutableStateOf(setParam) -------------- src/test/test.kt:30:Warning: Creating a MutableState object with a mutable collection type [MutableCollectionMutableState] val mapParameter = mutableStateOf(mapParam) -------------- src/test/test.kt:31:Warning: Creating a MutableState object with a mutable collection type [MutableCollectionMutableState] val collectionProperty = mutableStateOf(collectionParam) -------------- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Here is the source file referenced above: `src/test/test.kt`: ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~kotlin linenumbers package test import androidx.compose.runtime.* val list = mutableListOf(1) val set = mutableSetOf(1) val map = mutableMapOf(1 to 1) val collection: MutableCollection = list val listFunction = mutableStateOf(mutableListOf(1)) val listProperty = mutableStateOf(list) val setFunction = mutableStateOf(mutableSetOf(1)) val setProperty = mutableStateOf(set) val mapFunction = mutableStateOf(mutableMapOf(1 to 1)) val mapProperty = mutableStateOf(map) val collectionProperty = mutableStateOf(collection) fun test( listParam: MutableList, setParam: MutableSet, mapParam: MutableMap, collectionParam: MutableCollection ) { val listParameter = mutableStateOf(listParam) val setParameter = mutableStateOf(setParam) val mapParameter = mutableStateOf(mapParam) val collectionProperty = mutableStateOf(collectionParam) } ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 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/MutableCollectionMutableStateDetectorTest.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, `MutableCollectionMutableStateDetector.mutableCollection_stdlib`. 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("MutableCollectionMutableState") fun method() { mutableStateOf(...) } ``` or ```java // Java @SuppressWarnings("MutableCollectionMutableState") void method() { mutableStateOf(...); } ``` * Using a suppression comment like this on the line above: ```kt //noinspection MutableCollectionMutableState 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="MutableCollectionMutableState" 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 'MutableCollectionMutableState' } ``` In Android projects this should be nested inside an `android { }` block. * For manual invocations of `lint`, using the `--ignore` flag: ``` $ lint --ignore MutableCollectionMutableState ...` ``` * Last, but not least, using baselines, as discussed [here](https://googlesamples.github.io/android-custom-lint-rules/usage/baselines.md.html).