Automating Data Conversion in a Multi-Flavored Application

In my application, we need to build multiple versions from a single codebase. Each version, or flavor, requires different embedded data files. To manage this, we created a conversion script that must be run each time we switch to a different flavor. However, developers sometimes forget to run this script, leading to incorrect data in the application.

To solve this, I wanted to automate the conversion script to run automatically before building the application. Here’s how I achieved this.

Initial Attempt

After some investigation, I found that we could create a task in build.gradle.kts and make the assemble tasks depend on this conversion task. Here's the initial code I used:

fun createConvertTask(appFlavor: String) {
    val taskName = getAppFlavorConvertTaskName(appFlavor)
    tasks.register(taskName, org.gradle.api.tasks.Exec::class) {
        // Set the description and group for better organization and clarity in Gradle tasks
        description = "Converts data for $appFlavor flavor"
        group = "Conversion"

        // Set the working directory to the parent directory
        workingDir = file("$projectDir/..")

        // Set the command line to run the script with the app flavor as argument
        commandLine("sh", "./convert.sh", appFlavor)
    }
}

Since tasks can be added dynamically, we used a callback on tasks.whenTaskAdded to ensure our conversion task runs before the assemble tasks:

    if (name.startsWith("assemble") && !name.endsWith("Test")) {
        // Updated regex to handle specific build types 'Debug' or 'Release'
        val regex = Regex("assemble([A-Z][^A-Z]*)(Debug|Release)")

        val matchResult = regex.find(name)

        if (matchResult != null) {
            val (appFlavor, _) = matchResult.destructured
            this.dependsOn(getAppFlavorConvertTaskName(appFlavor))
        }
    }
}

However, when attempting to build the release version of the app, we encountered the following error:

ERROR: <app_root>/build/intermediates/merged_java_res/<app_release>/base.jar: R8: com.android.tools.r8.ResourceException: com.android.tools.r8.internal.Ub: I/O exception while reading '<app_root>/build/intermediates/merged_java_res/<app_release>/base.jar': <app_root>/build/intermediates/merged_java_res/<app_release>/base.jar

Solution

To resolve this issue, I moved the configuration to the afterEvaluate block. This ensures that all tasks are fully configured before we add dependencies. Here’s the final solution:

afterEvaluate {
    tasks.withType<DefaultTask>().configureEach {
        val regex = Regex("assemble([A-Z][^A-Z]*)(Debug|Release)")

        val matchResult = regex.find(name)

        if (matchResult != null) {
            val (appFlavor, _) = matchResult.destructured
            this.dependsOn(getAppFlavorConvertTaskName(appFlavor))
        }
    }
}

With this change, the APK builds successfully, and the conversion script runs automatically, ensuring the correct data files are embedded for each flavor.