The Android lint tool is a static code analysis tool that checks your Android project source files for potential bugs and optimization improvements for correctness, security, performance, usability, accessibility, and internationalization. Lint comes with over 200 checks, however it can be extended with additional custom rules.

NOTE: The lint API is not a final API; if you rely on this be prepared to adjust your code for the next tools release.

The Android Lint API allows users to create custom lint rules. For example, if you are the author of a library project, and your library project has certain usage requirements, you can write additional lint rules to check that your library is used correctly, and then you can distribute those extra lint rules for users of the library. Similarly, you may have company-local rules you'd like to enforce.

This sample demonstrates how to create a custom lint checks and corresponding tests for those rules.

This project shows how Android Studio 4 handles packaging of lint rules.

First, there's the lint check implementation itself. That's done in the "checks" project, which just applies the Gradle "java" plugin, and that project produces a jar. Note that the dependencies for the lint check project (other than its testing dependencies) must all be "compileOnly":

dependencies {
    compileOnly "com.android.tools.lint:lint-api:$lintVersion"
    compileOnly "com.android.tools.lint:lint-checks:$lintVersion"
	...

Next, there's a separate Android library project, called "library". This library doesn't have any code on its own (though it could). However, in its build.gradle, it specifies this:

dependencies {
    lintPublish project(':checks')
}

This tells the Gradle plugin to take the output from the "checks" project and package that as a "lint.jar" payload inside this library's AAR file. When that's done, any other projects that depends on this library will automatically be using the lint checks.

Note that you don't have to go through the extra "library indirection" if you have a lint check that you only want to apply to one or more app modules. You can simply include the lintChecks dependency as shown above there as well, and then lint will include these rules when analyzing the project.

The lint version of the libraries (specified in this project as the lintVersion variable in build.gradle) should be the same version that is used by the Gradle plugin.

If the Gradle plugin version is X.Y.Z, then the Lint library version is X+23.Y.Z.

git clone https://github.com/googlesamples/android-custom-lint-rules.git
cd android-custom-lint-rules

When building your own rules, you will likely want to know which dependencies you should bring into your own project. The below descriptions of the dependencies included within this project serve to help you make that decision:

Source Dependencies

• com.android.tools.lint:lint-api: The most important one; it contains things like LintClient, the Detector base class, the Issue class, and everything else that Lint checks rely on in the Lint framework.
• com.android.tools.lint:lint-checks: Contains the built-in checks that are developed internally. Also contains utilities that are sometimes useful for other lint checks, such as the VersionChecks class (which figures out whether a given UAST element is known to only be called at a given API level, either by surrounding if >= SDK-version checks or if < SDK-version early returns in the method).

Test Dependencies

• com.android.tools.lint:lint-tests: Contains useful utilities for writing unit tests for Lint checks, including the LintDetectorTest base class.
• com.android.tools:testutils: It's unlikely that you need to depend on this directly. The test infrastructure depends on it indirectly though (the methods we use there were mostly for the older lint test infrastructure, not the newer one).
• com.android.tools.lint:lint: Lint checks don't need to depend on this. It's a separate artifact used by tools that want to integrate lint with the command line, such as the Gradle integration of lint. This is where things like terminal output, HTML reporting, command line parsing etc is handled.

• The "lint-dev" Google group: https://groups.google.com/forum/#!forum/lint-dev
• Stack Overflow: http://stackoverflow.com/questions/tagged/android

If you've found an error in this sample, please file an issue: https://github.com/googlesamples/android-custom-lint-rules/issues

Patches are encouraged, and may be submitted by forking this project and submitting a pull request through GitHub.

Licensed under the Apache 2.0 license. See the LICENSE file for details.

Please read and follow the steps in the CONTRIBUTING.md