Sharing Gradle Configuration in Multi-Module Android Projects

Using multiple modules in our Android projects help us split apart our code into logical components.  They also can enable faster incremental builds, and more modular code.  One problem with multi-module projects is that there is a lot of verboseness of configuration.  This post shows you a method of sharing common configuration between your Android Library modules in order to cut down on boilerplate Gradle configuration.

I made this change in a PR in my ShoppingApp project on GitHub and ended up deleting a net 90 lines of code over 7 library modules.

apply from: “____.gradle”

You can add the contents of another Gradle file into your current one by using “apply from: ” and specifying the file whose content you want to add.

apply from: "$rootProject.projectDir/android-library.gradle"

$rootProject.projectDir

Modules can exist in different directory structures, so by leveraging the $rootProject.projectDir property, we specify paths based on the root project directory.

Original Library Module build.gradle

apply plugin: 'com.android.library'
apply plugin: 'kotlin-android'

android {
    compileSdkVersion Versions.compile_sdk

    defaultConfig {
        minSdkVersion Versions.min_sdk
        targetSdkVersion Versions.target_sdk
        versionCode 1
        versionName "1.0"

        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
    }
}

dependencies {
    implementation project(Modules.models)
    implementation Libs.kotlin_std_lib
}

Resulting Library Module build.gradle

apply from: "$rootProject.projectDir/android-library.gradle"

dependencies {
    implementation project(Modules.models)
    implementation Libs.kotlin_std_lib
}

Shared Gradle File

apply plugin: 'com.android.library'
apply plugin: 'kotlin-android'

android {
    compileSdkVersion Versions.compile_sdk

    defaultConfig {
        minSdkVersion Versions.min_sdk
        targetSdkVersion Versions.target_sdk
        versionCode 1
        versionName "1.0"

        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
    }
}

If You Do Something 3+ Times, Extract Out Functionality

Whenever it’s possible and makes sense, use common configuration to reduce boilerplate.  This same rule applies if you are writing code, or writing Android Gradle configuration.  This post shares an “easy win”, that you may be able to use to help better manage your multi-module project. There is so much more you can do to clean up your builds by leveraging buildSrc where you can write in Kotlin, Java or Groovy, but that’s for another post.

“It Depends” Is The Answer To Your Android Question

Android Questions:

  • Should I use Flutter? “It Depends”
  • Should I wrap a 3rd party library’s API? “It Depends”
  • Should I install the Android Q Beta? “It Depends”
  • Should I use Dagger? “It Depends”
  • Should I use Kotlin or Java? “It Depends”
  • Should I use React Native? “It Depends”
  • Should I use Dependency Injection? “It Depends”
  • Should I use OkHttp? “It Depends”
  • Should I use Multiple Activities or a Single Activity? “It Depends”
  • Should I upgrade to the latest Support Library? “It Depends”
  • Should I use a library that’s in Alpha? “It Depends”
  • Should I use Room or SqlDelight? “It Depends”
  • Should I write Espresso tests? “It Depends”
  • Should I bump my minSdk to 28? “It Depends”
  • Should I use MVP or MVVM or MVI or MVC? “It Depends”
  • Should I use RxJava or LiveData? “It Depends”
  • Should I learn Android or iOS? “It Depends”
  • Should I start a blog? “It Depends”
  • Should I start a side project? “It Depends”
  • … Insert Your Question Here  … “It Depends”

“It Depends” Is Technically Correct 💯% of the Time

While “It Depends” is technically correct since there is no absolute answer in software, it still doesn’t make it a good answer.  “Probably Should” is an answer well, but when you think about it, it’s still a variation of “It Depends”.

“It Depends” Is a Crappy Answer

Juhani brings up a great point about responsibility in his tweet above.  Opinions are great because they are shaped by experience.  As you gain experience, it’s important to share your opinions and discoveries because they will help provide insight and context into a topic.  That empowers the person searching for the answer to make a decision, because you can’t write software with “It Depends”, since it won’t compile. 😂

There Is No Perfect Answer

My goal of this post was to point out that there are tons of ways to do things, but based on your team, use case and target audience, there is no good 100% right answer for any topic.  I can strongly urge you to use Kotlin, but if you are building something that people are willing to pay millions of dollars from and they need Java, then Java is your right answer.  The important part is to keep listening to opinions and discoveries that are brought up, but know they are not a one-size-fits-all solution.

I’m happy to share my opinion and experiences with you on any topic if you reach out to me on Twitter @HandstandSam, and I’ll do my best not to answer with “It Depends”. 🙂