Why does Gradle only include classes from my library with project dependency

Question

I'm building an Android app that has a dependency on a custom library, and Gradle is only willing to include my custom library when I use a project dependency, not when I use a files dependency to include the library's jar file. I'm building both my app and the library with the API levee 19 SDK.

failing dependencies section from build.gradle:

dependencies {
  compile 'com.android.support:appcompat-v7:+'
  compile files('libs/MyLibrary.jar')
}

If I use the above dependencies section, none of the class in MyLibrary.jar are included in the build apk file, as verified by extracting its classes.dex and running dexdump. I have also verified that all of the classes are present in the jar file I'm using.

If I use the following dependencies section, then all of the classes in MyLibrary are included in the apk file:

dependencies {
  compile 'com.android.support:appcompat-v7:+'
  compile project(':MyLibrary')
}

I'm using Android Studio 0.4.0, Gradle 1.9, and I think the Gradle plugin 0.7.1.

What is going on here? I'd really like to build my app with the API level 18 sdk to test compatibility, but I can't get that working unless I'm able to just use the jar file for my library.

Answer 1

Okay, this was my fault. My library's build.gradle was configured to only include the source files in the jar output file. The following is incorrect Gradle code and will give you the same problems as I've had.

task jar(type: Jar) {
  from android.sourceSets.main.java
}

This answer shows how to fix the jar file creation. It's ugly, but it seems to work.