AndroidX is a fairly large project with 300+ modules which makes it a very resource heavy project for local development.
Playground setup allows sub projects to have an additional settings.gradle file that can be run independent of the main project. It also allows using external resources for artifacts such that just checking out the AndroidX git repository is enough without the prebuilt repositories that are needed by the main AndroidX project.
These project setups are only meant to be used for local development and all CI tasks run using the root AndroidX project.
A playground project needs a settings.gradle file that includes the playground-common/playground-plugin build and applies the playground plugin.
The playground plugin provides functionality allowing the playground project to be executed independently of the main AndroidX build, and to pull select projects from AndroidX.
To share as much common configuration as possible, it is also recommended to symlink some common files like gradle and .idea configuration.
To do that, execute “setup-playground.sh” command in your playground directory.
cd room; ../playground-common/setup-playground.sh
This script will create symbolic links for gradle and .idea files that are committed to the git repository. It also force adds the .idea files to the git repository because by default any nested .idea folder is ignored from git.
The playground plugin sets a pre-defined build file (playground-build.gradle) for the root project and also provides a playground extension for settings.gradle with useful configuration methods.
The custom settings.gradle file should first call setupPlayground("..") on the playground extension to establish the main configuration, providing the relative path of the playground project to the main AndroidX project.
After running setupPlayground, it can either include projects via includeProject method or filter projects from the main AndroidX settings gradle file using the selectProjectsFromAndroidX method.
When a gradle.properties file shows up under a sub project, main AndroidX build ends up reading it. For this reason, we can only keep a minimal gradle.properties file in these sub modules that also support playground setup.
We cannot avoid creating gradle.properties as certain properties (e.g. useAndroidX) are read at configuration time and we cannot set it dynamically.
Properties that will be set dynamically are kept in playground.properties file while shared properties are kept in androidx-shared.properties file. The dynamic properties are read in the playground plugin and set on each project.
There is a VerifyPlaygroundGradleConfigurationTask task that validates the contents of androidx-shared.properties file as part of the main AndroidX build.
Even though sub-projects usually declare exact coordinates for their dependencies, for tests, it is a common practice to declare project dependencies. To avoid needing to include all of those projects to make the build file work, AndroidXPlaygroundRootPlugin adds a projectOrArtifact method to each sub project. This function can be used instead of project to declare optional project dependencies. This function will return the project if it exists or default to its latest artifact if it doesn't.
Note that range artifacts are not allowed in the main AndroidX build so when the sub project is opened as part of the main AndroidX build, projectOrArtifact always resolves to the project. In playground projects, it always resolves to the latest SNAPSHOT artifact that is included in the playground build.