Create an AAR with multiple AARs/JARs - android-gradle-plugin

Question

I have seen questions (Android Studio combine 2 .aar into one and others) posted by various developers but I haven't seen a definitive response that enables me to create an AAR that includes 1 or more AARs or JARs (I can do with JARs since I don't need to share any resources; only classes). Here is the app.gradle for my library project:
apply plugin: 'com.android.library'
android {
compileSdkVersion 19
buildToolsVersion "19.1.0"
defaultConfig {
minSdkVersion 16
targetSdkVersion 21
}
buildTypes {
release {
minifyEnabled false
proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.txt'
}
}
}
dependencies {
compile 'com.google.code.gson:gson:2.1'
compile ('libs/eventbus.jar')
compile project(':core-release')
compile project(':midware-release')
}
Again, this app is a library project which needs two other library projects ('core-release', 'midware-release') and while I was able to generate one AAR file that I can use in my application, the application was unable to find the dependent library projects' classes so, I had to add the two library projects' AARs into my application.
Here is the app.gradle application project (without adding the JARs manually) which is unable to find the dependent projects' classes:
apply plugin: 'com.android.application'
android {
compileSdkVersion 23
buildToolsVersion "23.0.1"
defaultConfig {
applicationId "com.app.sample"
minSdkVersion 19
targetSdkVersion 23
versionCode 1
versionName "1.0"
}
buildTypes {
release {
minifyEnabled false
proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
}
}
}
dependencies {
compile fileTree(dir: 'libs', include: ['*.jar'])
testCompile 'junit:junit:4.12'
compile 'com.android.support:appcompat-v7:23.1.1'
compile 'com.android.support:design:23.1.1'
compile files('libs/eventbus.jar')
compile project(':sdk3-debug')
}
I don't think the library project's AAR file is pulling in the dependent projects (AAR or JAR) and hence the application is unable to find the classes.
I read about transitive dependency, but I was unable to find an example implementation which may help with my situation.

Answer 1

I haven't seen a definitive response that enables me to create an AAR that includes 1 or more AARs or JARs.
Yes, I think because this topic is not limited to AAR or JAR, but how Maven manage dependency.
https://maven.apache.org/guides/introduction/introduction-to-dependency-mechanism.html
while I was able to generate one AAR file that I can use in my application, the application was unable to find the dependent library projects' classes so, I had to add the two library projects' AARs into my application.
It's not your AAR responsibility to include your dependencies, your POM file should include information about dependencies.
https://maven.apache.org/pom.html
I don't think the library project's AAR file is pulling in the dependent projects (AAR or JAR) and hence the application is unable to find the classes.
Correct, you still need to include libraries dependency in your Application.
I assume you want your library can be used by Application, without specifying your library dependencies core-release and midware-release. I made a full explanation here android studio generate aar with dependency but here is what you need to do:
Upload core-release and midware-release to your Maven repository
Create a POM file for your library that include your dependencies
<project>
<modelVersion>4.0.0</modelVersion>
<parent>...</parent>
<artifactId>okhttp</artifactId>
<name>OkHttp</name>
<dependencies>
<dependency>
<groupId>com.example</groupId>
<artifactId>core-release</artifactId>
</dependency>
<dependency>
<groupId>com.example</groupId>
<artifactId>midware-release</artifactId>
</dependency>
</dependencies>
<build>...</build>
</project>
Publish your AAR with that POM file
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:mavenPassword#nexus.example.com/repository/maven-releases/"
And then your Application can use your library. Gradle will download your library transitive dependencies automatically.

Answer 2

I was able to address the issue by following Stan Kurdziel 's suggestion: stackoverflow.com/questions/30052058/multiple-aar-files and here are steps I took to arrive at a solution:
I created an AAR which I published to the local maven repository
Now this AAR was accessible in the application project
This AAR also had reference to the classes in the core and midware libraries. I followed Stan Kurdziel's approach #2:
Manually add the dependency on Library Project 2 to the Application Project - so that your Application has a dependency line for both Libraries. Depending on your specific situation this may or may not be a workable solution.
Hope this helps others that might run into similar issue.

Answer 3

This should fix your issue:
dependencies {
compile fileTree(dir: 'libs', include: ['*.jar'])
testCompile 'junit:junit:4.12'
compile 'com.android.support:appcompat-v7:23.1.1'
compile 'com.android.support:design:23.1.1'
compile files('libs/eventbus.jar')
compile project(':sdk3-debug') { transitive = true }
}
Include the transitive flag at true.