This recipe shows how you can adapt a built-in Gradle Task using intrinsic file types like File in order to be
compatible with the new Variant API. The new variant API requires using instances of Property<> when wiring
things up in order to carry task dependency within those property objects. This is not easy when you want to use
an old task expressing its input or output using File for instance.
In this example, we add a source folder to Android's assets. The source folder
content is provided by a org.gradle.api.tasks.Copy
Task which expresses its output folder using a
File
In this recipe, we use the SourceDirectories.addGeneratedSourceDirectory to add a new folder for assets
processing using Gradle's Copy Tasks.
| Module | Content |
|---|---|
| build-logic | Contains the Project plugin that is the core of the recipe. |
| app | An Android application that will be configured with the added source folder. |
When you need to bridge a Task output expressed using a File
to a Provider which is expected by the variant API, you cannot just create a DirectoryProperty using
Gradle's 'ObjectFactory' and call set() with the File instance. Although the value would be set correctly, the
Property object would not carry the Task dependency which would eventually yield to a failure :
':projectA:someTask' uses this output of task ':projectA:generatingAssetTask' without declaring an explicit or
implicit dependency. This can lead to incorrect results being produced, depending on what order the tasks are executed.
In order for gradle to set the property object correctly, you must do a map
or flatMap
using the TaskProvider of the generating Task.
The easiest way to do that is to subclass the original Task and override the right methods to redirect the input or output values to properties. In our case, the subclass is simply :
abstract class PropertyBasedCopy: Copy() {
@get:OutputDirectory
abstract val outputDirectory: DirectoryProperty
override fun getDestinationDir(): File =
outputDirectory.get().asFile
override fun setDestinationDir(destination: File) {
outputDirectory.set(destination)
}
}
Once the TaskProvider is created, you need to use SourceDirectories.addGeneratedSourceDirectory to register its
output as a new source folder.
variant.sources.assets?.addGeneratedSourceDirectory(
propertyBasedCopyTaskProvider,
PropertyBasedCopy::outputDirectory)
To run the examples, you can just do:
./gradlew debugVerifyAsset