(#) Use KTX extension function !!! WARNING: Use KTX extension function This is a warning. Id : `UseKtx` Summary : Use KTX extension function Severity : Warning Category : Productivity Platform : Android Vendor : Android Open Source Project Feedback : https://issuetracker.google.com/issues/new?component=192708 Since : 8.9.0 (March 2025) Affects : Kotlin and Java files Editing : This check runs on the fly in the IDE editor Implementation : [Source Code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-checks/src/main/java/com/android/tools/lint/checks/UseKtxDetector.kt) Tests : [Source Code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-tests/src/test/java/com/android/tools/lint/checks/UseKtxDetectorTest.kt) The Android KTX libraries decorates the Android platform SDK as well as various libraries with more convenient extension functions available from Kotlin, allowing you to use default parameters, named parameters, and more. !!! Tip This lint check has an associated quickfix available in the IDE. (##) Options You can configure this lint checks using the following options: (###) remove-defaults Whether to skip arguments that match the defaults provided by the extension. Extensions often provide default values for some of the parameters. For example: ```kotlin fun Path.readLines(charset: Charset = Charsets.UTF_8): List { return Files.readAllLines(this, charset) } ``` This lint check will by default automatically omit parameters that match the default, so if your code was calling ```kotlin Files.readAllLines(file, Charset.UTF_8) ``` lint would replace this with ```kotlin file.readLines() ``` rather than ```kotlin file.readLines(Charset.UTF_8 ``` You can turn this behavior off using this option. Default is true. Example `lint.xml`: ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~xml linenumbers <lint> <issue id="UseKtx"> <option name="remove-defaults" value="true" /> </issue> </lint> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ (###) require-present Whether to only offer extensions already available. This option lets you only have lint suggest extension replacements if those extensions are already available on the class path (in other words, you're already depending on the library containing the extension method.) Default is true. Example `lint.xml`: ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~xml linenumbers <lint> <issue id="UseKtx"> <option name="require-present" value="true" /> </issue> </lint> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ (##) Example Here is an example of lint warnings produced by this check: ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~text src/test/pkg/test.kt:5:Warning: Use the KTX extension function String.htmlEncode instead? [UseKtx] val html = TextUtils.htmlEncode("Is x > y ?") ---------------------------------- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Here is the source file referenced above: `src/test/pkg/test.kt`: ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~kotlin linenumbers package test.pkg import android.text.TextUtils fun test() { val html = TextUtils.htmlEncode("Is x > y ?") } ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ You can also visit the [source code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-tests/src/test/java/com/android/tools/lint/checks/UseKtxDetectorTest.kt) for the unit tests for this check to see additional scenarios. (##) 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("UseKtx") fun method() { problematicStatement() } ``` or ```java // Java @SuppressWarnings("UseKtx") void method() { problematicStatement(); } ``` * Using a suppression comment like this on the line above: ```kt //noinspection UseKtx 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="UseKtx" 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 'UseKtx' } ``` In Android projects this should be nested inside an `android { }` block. * For manual invocations of `lint`, using the `--ignore` flag: ``` $ lint --ignore UseKtx ...` ``` * Last, but not least, using baselines, as discussed [here](https://googlesamples.github.io/android-custom-lint-rules/usage/baselines.md.html).