How to Include a Library Module Dependency in an Android Studio Project

How to include a library module dependency in an Android Studio project?

Android Studio works on project-modules concept,All your modules should be inside a root directory(Your Project Directory). One module can be depended on other module/modules. Your libraries are considered as different modules under same project and your main module(app in your case) depends on them.

Change your project structure a little bit :

Project Root
+-- libs
    +-- PullToRefresh (my lib project)
+-- app
|   +-- builds
|   +-- src
|   |   +-- main (java code and resources)
    +-- .....
+--settings.gradle

Include this line in your settings.gradle

include ':libs:PullToRefresh'

Your build.gradle looks fine. I suggest you to change your directory name from libs to library because use libs for your jar dependency not for module dependencies.

and keep this in your main module's build.gradle file :

dependencies {
    compile project(":libs:PullToRefresh")
}

Importing Module in Android Studio

Steps to import Module in Android Studio 3.3 and lower.

1. Go to File >> New >> Import Module...
2. Select the source directory of the Module you want to import and click Finish.
3. Open Project Structure and open Module Settings for your project.
4. Open the Dependencies tab.
5. Click the (+) icon and select Module Dependency. Select the module and click Ok.
6. Open your build.gradle file and check that the module is now listed under dependencies.implementation project(path: ':ViewPagerIndicator')

Steps to import Module in Android Studio 3.4 and higher (See attached
image).

1. Go to File >> New >> Import Module...
2. Select the source directory of the Module you want to import and click Finish.
3. Open Project Structure Dialog (You can open the PSD by selecting File > Project Structure) and from the left panel click on Dependencies.
4. Select the module from the Module(Middle) section In which you want to add module dependency.
5. Click the (+) icon from the Declared Dependencies section and click Module Dependency.
6. Select the module and click Ok.
7. Open your build.gradle file and check that the module is now listed under dependencies.implementation project(path: ':ViewPagerIndicator')
   

Library module dependency Vs App module dependencies

why do I have to add same dependencies in app module also?

This is because dependencies are not shipped along with your .aar/.jar file. The compile time binding exists, due to which your library compiles, but in order to have runtime implementation, you need to include those libraries in your app module.

Can it be improved?

Can do that but ideally you should let the app module provide the dependencies. This is because, if two libraries ship with their dependencies, which could be used by both, then the common dependencies would be duplicated and overlap each other. This will cause build issues.

If you still want to proceed (may be you have internal module which is proprietary) then you can either extract the dependency libraries jar and include it in libs directory or publish it in maven along with the dependencies.

How do I add a library project to Android Studio?

Update for Android Studio 1.0

Since Android Studio 1.0 was released (and a lot of versions between v1.0 and one of the firsts from the time of my previous answer) some things has changed.

My description is focused on adding external library project by hand via Gradle files (for better understanding the process). If you want to add a library via Android Studio creator just check the answer below with visual guide (there are some differences between Android Studio 1.0 and those from screenshots, but the process is very similar).

Before you start adding a library to your project by hand, consider adding the external dependency. It won’t mess in your project structure. Almost every well-known Android library is available in a Maven repository and its installation takes only one line of code in the app/build.gradle file:

dependencies {
     implementation 'com.jakewharton:butterknife:6.0.0'
}

Adding the library

Here is the full process of adding external Android library to our project:

1. Create a new project via Android Studio creator. I named it HelloWorld.
2. Here is the original project structure created by Android Studio:

HelloWorld/
      app/
           - build.gradle  // local Gradle configuration (for app only)
           ...
      - build.gradle // Global Gradle configuration (for whole project)
      - settings.gradle
      - gradle.properties
      ...

3. In the root directory (HelloWorld/), create new folder: /libs in which we’ll place our external libraries (this step is not required - only for keeping a cleaner project structure).
4. Paste your library in the newly created /libs folder. In this example I used PagerSlidingTabStrip library (just download ZIP from GitHub, rename library directory to „PagerSlidingTabStrip" and copy it). Here is the new structure of our project:

HelloWorld/
      app/
           - build.gradle  // Local Gradle configuration (for app only)
           ...
      libs/
           PagerSlidingTabStrip/
                - build.gradle // Local Gradle configuration (for library only)
      - build.gradle // Global Gradle configuration (for whole project)
      - settings.gradle
      - gradle.properties
      ...

5. Edit settings.gradle by adding your library to include. If you use a custom path like I did, you have also to define the project directory for our library. A whole settings.gradle should look like below:

    include ':app', ':PagerSlidingTabStrip'
    project(':PagerSlidingTabStrip').projectDir = new File('libs/PagerSlidingTabStrip')
   

5.1 If you face "Default Configuration" error, then try this instead of step 5,

    include ':app'
    include ':libs:PagerSlidingTabStrip'

6. In app/build.gradle add our library project as an dependency:

    dependencies {
        implementation fileTree(dir: 'libs', include: ['*.jar'])
        implementation 'com.android.support:appcompat-v7:21.0.3'
        implementation project(":PagerSlidingTabStrip")
    }
   

6.1. If you followed step 5.1, then follow this instead of 6,

    dependencies {
        implementation fileTree(dir: 'libs', include: ['*.jar'])
        implementation 'com.android.support:appcompat-v7:21.0.3'

        implementation project(":libs:PagerSlidingTabStrip")
    }

7. If your library project doesn’t have build.gradle file you have to create it manually. Here is example of that file:

        apply plugin: 'com.android.library'
   
        dependencies {
            implementation 'com.android.support:support-v4:21.0.3'
        }
   
        android {
            compileSdkVersion 21
            buildToolsVersion "21.1.2"
   
            defaultConfig {
                minSdkVersion 14
                targetSdkVersion 21
            }
   
            sourceSets {
                main {
                    manifest.srcFile 'AndroidManifest.xml'
                    java.srcDirs = ['src']
                    res.srcDirs = ['res']
                }
            }
        }
   

8. Additionally you can create a global configuration for your project which will contain SDK versions and build tools version for every module to keep consistency. Just edit gradle.properties file and add lines:

    ANDROID_BUILD_MIN_SDK_VERSION=14
    ANDROID_BUILD_TARGET_SDK_VERSION=21
    ANDROID_BUILD_TOOLS_VERSION=21.1.3
    ANDROID_BUILD_SDK_VERSION=21
   

   Now you can use it in your build.gradle files (in app and libraries modules) like below:

    //...
    android {
        compileSdkVersion Integer.parseInt(project.ANDROID_BUILD_SDK_VERSION)
        buildToolsVersion project.ANDROID_BUILD_TOOLS_VERSION
   
        defaultConfig {
            minSdkVersion Integer.parseInt(project.ANDROID_BUILD_MIN_SDK_VERSION)
            targetSdkVersion Integer.parseInt(project.ANDROID_BUILD_TARGET_SDK_VERSION)
        }
    }
    //...
   

9. That’s all. Just click‚ synchronise the project with the Gradle’ icon . Your library should be available in your project.

Google I/O 2013 - The New Android SDK Build System is a great presentation about building Android apps with Gradle Build System: As Xavier Ducrohet said:

Android Studio is all about editing, and debugging and profiling.
It's not about building any more.

At the beginning it may be little bit confusing (especially for those, who works with Eclipse and have never seen the ant - like me ;) ), but at the end Gradle gives us some great opportunities and it worth to learn this build system.

Add local Library Project as a dependency to multiple Projects in Android Studio

You can also refer to a library outside of your project folder using the project().projectDir property. If your external library is relative to your project like so

- MyLibrary
   - library
- MyProject
    - app

in MyProject/settings.gradle

include ':library'
project(':library').projectDir = new File(settingsDir, '../MyLibrary/library')

in MyProject/app/build.gradle

dependencies {
   compile project(':library')
}

Adding external library in Android studio

Try this:

File > Project Structure > Dependencies Tab > Add module dependency (scope = compile)

Where the module dependency is the project library Android folder.

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