How to share a single library source across multiple projects

Question as in title. A similar question was asked here, and the only workaround that time was to publish the project into a local Maven repository.

Is this problem fixed (as claimed by some) in Android Studio 0.5.+? In its release note there is a statement that says "Support for source folders outside the module content root". Does that mean we can finally import the library from outside the project folder?

I tried File->Import Project.. but it doesn't work.

EDIT 2: See accepted answer for latest solution (as of 0.8.+)

EDIT:

My project directory structure has only one module main which looks like this

MyApp
    main
        build.gradle
        src
    build.gradle
    settings.gradle

The library project directory has only one module named like lib (they are all auto-generated when creating a new library project)

MyLibrary
    lib
        build.gradle
        src
    build.gradle
    settings.gradle

The following line is added into MyApp/settings.gradle:

include ':main', '..:MyLibrary'

The following is added into MyApp/main/build.gradle:

dependencies {
    compile project(':..:MyLibrary')
}

The result is the following error:

FAILURE: Build failed with an exception.

* What went wrong:
A problem occurred configuring project ':main'.
> Configuration with name 'default' not found.

As a side note, the library project MyLibrary itself can compile without error. The problem seems to be settings.gradle not being able to recognize the library project structure.

Solution 1:

(as of version 2.1+):

Below are the steps that I took to share library source outside of the project directory. Instead of plain Java library, my codes are compiled as Android module, but that library module is not contained inside the main project. It is fine with me as long as there are no code duplications and I only need to maintain one set of library code for all projects:

1) File->new Project. Give a name to your library project (here I use LibraryProject). Continue the remaining steps to create a normal project (since this is intended as a library, I chose "add no activity")

2) By default, Android studio creates the module named as "app" inside the project folder. To prevent names collision with the actual application module, rename the module to something else (Right click "app" module at left panel->Refactor->Rename).

3) In the build.gradle inside your library module folder, change the top line

apply plugin: 'com.android.application'

to

apply plugin: 'com.android.library'

and then remove the "applicationId" line under "defaultConfig". Also, since this is a library, remove the xlmns:... namespace and <application ..> body from Manifest.xml as well. That's all for the library part. Now, to create/modify your main application:

4) If it is a new project, first create new project File->new Project->ApplicationName.

5) Open settings.gradle (there should only be one such file in every project) and include the following line (note the missing leading semi-colon in library module):

include ':app', '..:LibraryProject:yourLibraryModule'

6) Then go to File->Project Structure.

7) Under the tab "Dependencies" click the green "+" button at right. Select "Module dependency". Choose your library module, then click OK.

You should now be able to use the library classes in your application.

ALTERNATIVE METHOD If, for some reason, there are still problems with the above method, you can try the following (suggested in here):

1) Repeat steps 1 to 4 above. By default the main and external (library) project look something like this:

  /MainProject
    + build.gradle
    + settings.gradle
    + app/
      + build.gradle
      + src/

  /LibraryProject
    + build.gradle
    + settings.gradle
    + app/
      + build.gradle
      + src/

2) As usual, refactor the modules name (in android studio right-click module->refactor->rename) to something less confusing, such as

  /MainProject
    + build.gradle
    + settings.gradle
    + MainModule/
      + build.gradle
      + src/

  /LibraryProject
    + build.gradle
    + settings.gradle
    + LibraryModule/
      + build.gradle
      + src/

3) Modify the settings.gradle in MainProject:

include ':LibraryModule', ':app'
project(':LibraryModule').projectDir = new File(settingsDir, '../LibraryProject/LibraryModule')

Sync the project and you're done.

Note on Proguard

Currently you should not use a proguard on external library projects/modules. Instead, you replace the following (original answer here)

buildTypes {
    release {
        minifyEnabled true
        proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-project.txt'
    }
    debug {
        minifyEnabled false
    }
}

with the following (in build.gradle of the library):

buildTypes {
    release {
        consumerProguardFiles 'proguard-project.txt'
    }
}

where proguard-project.txt is the file that contains the proguard rules for your library project.

Solution 2:

Yes, it works now in 0.5.0. There isn't a friendly UI to it (Import Project isn't what you want, as that creates an entirely new project; Import Module is still broken; see https://code.google.com/p/android/issues/detail?id=62122), but you can set up your build files to make it work.

Let's say you have a directory structure that looks like this:

MyApp
    appmodule
        build.gradle
            src
                main
                    java
    build.gradle
    settings.gradle
MyPlainJavaLibrary
    build.gradle
    src
        java

Note that MyPlainJavaLibrary isn't underneath the MyApp directory in the filesystem.

Set up your settings.gradle file like so:

include ':appmodule', '..:MyPlainJavaLibrary'

and include a dependency to it in build.gradle like this (don't forget the leading colon):

dependencies {
    ...
    compile project(':..:MyPlainJavaLibrary')
}

This works for me. In my Project viewer, I now see MyApp and MyPlainJavaLibrary as two root-level module directories in the view, and I can make java import statements work across module boundaries and such.

Note that in this default setup, this shared module will only have a single build output folder that will be shared among all the projects using it. This may or may not be what you want. If you'd like to have a different output directory for each project using the shared module, you can probably do some magic with the output directory in the sourceSet; if you want help with this, I'd recommend trying it out on your own and posting a question with details on your work if you get stuck.

You can only have one settings.gradle file per project, so this isn't going to take a whole other multimodule Gradle project and bring in all the modules in one fell swoop; you'll need to bring them in individually. However, it should satisfy the use case of using a module in multiple projects.