How to include aar files used in library projects in main project in Android

Question

My project is including some library project. Library is using some aar files and its dependecny is already defined in the module: gradle file. I am facing problem in including this library in my project.

If I keep duplicate aar files in app->lib and define their dependency in app->gradle file then there is no problem. But it shouldn't be the right approach.

Please find below the error:

A problem occurred configuring project ':app'.

Could not resolve all dependencies for configuration ':app:_qaDebugCompile'. Could not find :api-release:. Searched in the following locations:
         https://jcenter.bintray.com//api-release//api-release-.pom
         https://jcenter.bintray.com//api-release//api-release-.aar
         file:/D:/sample/sample-android-app/app/libs/api-release-.aar
         file:/D:/sample/sample-android-app/app/libs/api-release.aar
     Required by:
         sample-android-app:app:unspecified > sample-android-app:misnapworkflow:unspecified

please find below the project structure:

sample
|-- app
|-- misnapworkflow
    |
    |-- lib
        |-- api-release.aar

In app gradle file following has been mentioned to include the project

dependencies { compile project(':misnapworkflow') }

Please find below the misnapworkflow gradle file:

apply plugin: 'com.android.library'

android {
    compileSdkVersion 23
    buildToolsVersion "23.0.1"

    defaultConfig {
        minSdkVersion 10
        targetSdkVersion 23
        consumerProguardFiles 'proguard-rules.pro'
    }

    lintOptions {
        abortOnError false
    }

    // Publish both debug and release libraries
    publishNonDefault true

    buildTypes {
        debug {
            debuggable true
            jniDebuggable true
            minifyEnabled false
            shrinkResources false
            testCoverageEnabled true
        }

        release {
            signingConfig signingConfigs.debug
            debuggable false
            jniDebuggable false
            minifyEnabled true
            shrinkResources false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }
}

task grantPermissions(type: Exec, dependsOn: 'installDebugTest') {
    logger.warn('Granting permissions...')
    commandLine "adb shell pm grant com.miteksystems.misnap.misnapworkflow.test android.permission.WRITE_EXTERNAL_STORAGE".split(' ')
    commandLine "adb shell pm grant com.miteksystems.misnap.misnapworkflow.test android.permission.CAMERA".split(' ')
    logger.warn('Permissions granted.')
}

tasks.whenTaskAdded { task ->
    if (task.name.startsWith('connected')
            || task.name.startsWith('create')) {
        task.dependsOn grantPermissions
    }
}

dependencies {
    compile fileTree(include: ['*.jar'], dir: 'libs')
    compile 'com.android.support:appcompat-v7:23.0.1'

    // Add dependency for MiSnap external API
    compile(name: 'api-release', ext: 'aar')

    // Add dependency for MiSnap
    compile(name: 'misnap-release', ext: 'aar') {
        exclude module: 'appcompat-v7'
    }

    // Eventbus dependency
    compile 'de.greenrobot:eventbus:2.4.0'

    // Add OPTIONAL dependency for Manatee
    compile(name: 'manatee-release', ext: 'aar')

    compile(name: 'cardio-release', ext: 'aar')
}

repositories {
    flatDir {
        dirs 'libs'
    }
}

Answer 1

If I keep duplicate aar files in app->lib and define their dependency in app->gradle file then there is no problem. But it shouldn't be the right approach.

You're right, your app shouldn't define your AAR library dependencies in build.gradle. That's a common practice for 3rd party libraries like OkHttp, Picasso or RxJava. Those libraries are, in fact, has their own dependencies, just like your AAR library.

So, how come OkHttp, Picasso or RxJava doesn't ask your App to include their dependencies? Because they have included their dependencies on a POM file. A POM file contains configuration file for your AAR, including your artifact, group name, version, and its dependencies.

Let's take OkHttp as an example. OkHttp and its dependencies are stored in other people computer. Go to mvnrepository.com and search for OkHttp.

You will find OkHttp and its POM file.

<project>
   <modelVersion>4.0.0</modelVersion>
   <parent>...</parent>
   <artifactId>okhttp</artifactId>
   <name>OkHttp</name>
   <dependencies>
      <dependency>
         <groupId>com.squareup.okio</groupId>
         <artifactId>okio</artifactId>
      </dependency>
      <dependency>
         <groupId>com.google.android</groupId>
         <artifactId>android</artifactId>
         <scope>provided</scope>
      </dependency>
      <dependency>
         <groupId>com.google.code.findbugs</groupId>
         <artifactId>jsr305</artifactId>
         <scope>provided</scope>
      </dependency>
   </dependencies>
   <build>...</build>
</project>

When you include a library in your build.gradle(), Gradle will search that library on repositories define in top-level build.gradle. For OkHttp it was stored in mavenCentral().

repositories {
    google()
    mavenCentral()
    jcenter()
}

Gradle will download the dependencies automatically, you don't need to specify library dependency on your App project.

But it shouldn't be the right approach.

The right approach is:

1. Store your library and its dependencies in a Maven repository.

You can use local Maven repository, host your own Maven repo, or publish your library on Maven Central or Bintray. inthecheesefactory has a good tutorial for that.

2. Create a POM file for your library.

When you deploy your AAR you have to include POM file. It can be done manually.

mvn deploy:deploy-file \
    -DgroupId=com.example \
    -DartifactId=your-library \
    -Dversion=1.0.1 \
    -Dpackaging=aar \
    -Dfile=your-library.aar \
    -DpomFile=path-to-your-pom.xml \
    -DgeneratePom=true \
    -DupdateReleaseInfo=true \
    -Durl="https://mavenUserName:[email protected]/repository/maven-releases/"

Or using android-maven-publish Gradle plugin.

gradle yourlibrary:assembleRelease yourlibrary:publishMavenReleaseAarPublicationToMavenRepository

3. Share your library to your peers:

In app-level build.gradle add the GAV of your library.

dependencies{
    implementation "com.example:yourlibrary:1.0.1"
}

You and your peers should be able to use yourlibrary now.

Answer 2

The aar file doesn't contain the transitive dependencies and doesn't have a pom file which describes the dependencies used by the library.

It means that, if you are importing a aar file using a flatDir repo you have to specify the dependencies also in your project.

You should use a maven repository (you have to publish the library in a private or public maven repo), you will not have the same issue.
In this case, gradle downloads the dependencies using the pom file which will contains the dependencies list.