Creating a new Firebase SDK

1. Repository layout and Gradle
2. Creating an SDK
   1. Update firebase-foo.gradle.kts with the following content
   2. Create src/main/AndroidManifest.xml with the following content:
   3. Create com.google.firebase.foo.FirebaseFoo
   4. Create com.google.firebase.foo.FirebaseFooRegistrar

Want to create a new SDK in firebase/firebase-android-sdk? Read on.

Repository layout and Gradle

firebase/firebase-android-sdk uses a multi-project Gradle build to organize the different libraries it hosts. As a consequence, each project/product within this repo is hosted under its own subdirectory with its respective build file(s).

firebase-android-sdk
├── buildSrc
├── appcheck
│   └── firebase-appcheck
│   └── firebase-appcheck-playintegrity
├── firebase-annotations
├── firebase-common
│   └── firebase-common.gradle # note the name of the build file
│   └── ktx
│      └── ktx.gradle.kts # it can also be kts
└── build.gradle # root project build file.

Most commonly, SDKs are located as immediate child directories of the root directory, with the directory name being the exact name of the Maven artifact ID the library will have once released. e.g. firebase-common directory hosts code for the com.google.firebase:firebase-common SDK.

Note that the build file name for any given SDK is not build.gradle or build.gradle.kts but rather mirrors the name of the sdk, e.g. firebase-common/firebase-common.gradle or firebase-common/firebase-common.gradle.kts.

All of the core Gradle build logic lives in buildSrc and is used by all SDKs.

SDKs can be grouped together for convenience by placing them in a directory of choice.

Creating an SDK

Let’s say you want to create an SDK named firebase-foo

1. Create a directory called firebase-foo.
2. Create a file firebase-foo/firebase-foo.gradle.kts.
3. Add firebase-foo line to subprojects.cfg at the root of the tree.

Update firebase-foo.gradle.kts with the following content

plugins {
  id("firebase-library")
  // Uncomment for Kotlin
  // id("kotlin-android")
}

firebaseLibrary {
    // enable this only if you have tests in `androidTest`.
    testLab.enabled = true
    publishSources = true
    publishJavadoc = true
}

android {
  val targetSdkVersion : Int by rootProject
  val minSdkVersion : Int by rootProject

  compileSdk = targetSdkVersion
  defaultConfig {
    namespace = "com.google.firebase.foo"
    // change this if you have custom needs.
    minSdk = minSdkVersion
    targetSdk = targetSdkVersion
    testInstrumentationRunner = "androidx.test.runner.AndroidJUnitRunner"
  }

  testOptions.unitTests.isIncludeAndroidResources = true
}

dependencies {
  implementation("com.google.firebase:firebase-common:21.0.0")
  implementation("com.google.firebase:firebase-components:18.0.0")
}

Create src/main/AndroidManifest.xml with the following content:

<?xml version="1.0" encoding="utf-8"?>
<!-- Copyright 2024 Google LLC -->
<!-- -->
<!-- Licensed under the Apache License, Version 2.0 (the "License"); -->
<!-- you may not use this file except in compliance with the License. -->
<!-- You may obtain a copy of the License at -->
<!-- -->
<!--      http://www.apache.org/licenses/LICENSE-2.0 -->
<!-- -->
<!-- Unless required by applicable law or agreed to in writing, software -->
<!-- distributed under the License is distributed on an "AS IS" BASIS, -->
<!-- WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. -->
<!-- See the License for the specific language governing permissions and -->
<!-- limitations under the License. -->

<manifest xmlns:android="http://schemas.android.com/apk/res/android">
  <application>
      <service android:name="com.google.firebase.components.ComponentDiscoveryService"
          android:exported="false">
          <meta-data
              android:name="com.google.firebase.components:com.google.firebase.foo.FirebaseFooRegistrar"
              android:value="com.google.firebase.components.ComponentRegistrar" />
      </service>
  </application>
</manifest>

Create com.google.firebase.foo.FirebaseFoo

For Kotlin

class FirebaseFoo {
  companion object {
    @JvmStatic
    val instance: FirebaseFoo
      get() = getInstance(Firebase.app)

    @JvmStatic fun getInstance(app: FirebaseApp): FirebaseFoo = app.get(FirebaseFoo::class.java)
  }
}

For Java

public class FirebaseFoo {
  public static FirebaseFoo getInstance() {
    return getInstance(FirebaseApp.getInstance());
  }
  public static FirebaseFoo getInstance(FirebaseApp app) {
    return app.get(FirebaseFoo.class);
  }
}

Create com.google.firebase.foo.FirebaseFooRegistrar

For Kotlin

class FirebaseFooRegistrar : ComponentRegistrar {
  override fun getComponents() =
    listOf(
      Component.builder(FirebaseFoo::class.java).factory { container -> FirebaseFoo() }.build(),
      LibraryVersionComponent.create("fire-foo", BuildConfig.VERSION_NAME)
    )
}

For Java

public class FirebaseFooRegistrar implements ComponentRegistrar {
  @Override
  public List<Component<?>> getComponents() {
    return Arrays.asList(
        Component.builder(FirebaseFoo.class).factory(c -> new FirebaseFoo()).build(),
        LibraryVersionComponent.create("fire-foo", BuildConfig.VERSION_NAME));

  }
}

Continue to How Firebase works.