[android-studio] How to create a library project in Android Studio and an application project that uses the library project

I'm new to the gradle build system and IntelliJ.

So how do I create an Android Library Project (e.g. com.myapp.lib1) and the application project (e.g. com.myapp.app) and make the build system include com.myapp.lib1 on the application project?

I went to the Project Structure -> Modules -> My App project and added a dependency to the lib project. IntelliJ now can recognize classes from the lib project when used in the app project, but when I run the app project, there are errors like:

Gradle: error: package com.myapp.lib1 does not exist

The simplest way for me to create and reuse a library project:

1. On an opened project file > new > new module (and answer the UI questions)

2. check/or add if in the file settings.gradle: include ':myLibrary'

3. check/or add if in the file build.gradle:

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

4. To reuse this library module in another project, copy it's folder in the project instead of step 1 and do the steps 2 and 3.

You can also create a new studio application project You can easily change an existing application module to a library module by changing the plugin assignment in the build.gradle file to com.android.library.

apply plugin: 'com.android.application'

android {...}

to

apply plugin: 'com.android.library'

android {...}

more here

Purpose: Android library at single place - Share across multiple projects http://raevilman.blogspot.com/2016/02/android-library-project-using-android.html

I wonder why there is no example of stand alone jar project.

In eclipse, we just check "Is Library" box in project setting dialog.
In Android studio, I followed this steps and got a jar file.

1. Create a project.

2. open file in the left project menu.(app/build.gradle): Gradle Scripts > build.gradle(Module: XXX)

3. change one line: apply plugin: 'com.android.application' -> 'apply plugin: com.android.library'

4. remove applicationId in the file: applicationId "com.mycompany.testproject"

5. build project: Build > Rebuild Project

6. then you can get aar file: app > build > outputs > aar folder

7. change aar file extension name into zip

8. unzip, and you can see classes.jar in the folder. rename and use it!

Anyway, I don't know why google makes jar creation so troublesome in android studio.

For Intellij IDEA (and Android Studio) each library is a Module. Think of a Module in Android Studio as an equivalent to project in Eclipse. Project in Android Studio is a collection of modules. Modules can be runnable applications or library modules.

So, in order to add a new android library project to you need to create a module of type "Android library". Then add this library module to the dependency list of your main module (Application module).

Google’s Gradle Plugin recommended way for configuring your gradle files to build multiple projects has some shortcomings If you have multiple projects depending upon one library project, this post briefly explain Google’s recommended configuration, its shortcomings, and recommend a different way to configure your gradle files to support multi-project setups in Android Studio:

An alternative multiproject setup for android studio

A Different Way :

It turns out there’s a better way to manage multiple projects in Android Studio. The trick is to create separate Android Studio projects for your libraries and to tell gradle that the module for the library that your app depends on is located in the library’s project directory. If you wanted to use this method with the project structure I’ve described above, you would do the following:

1. Create an Android Studio project for the StickyListHeaders library
2. Create an Android Studio project for App2
3. Create an Android Studio project for App1
4. Configure App1 and App2 to build the modules in the StickyListHeaders project.

The 4th step is the hard part, so that’s the only step that I’ll describe in detail. You can reference modules that are external to your project’s directory by adding a project statement in your settings.gradle file and by setting the projectDir property on the ProjectDescriptor object that’s returned by that project statement:

The code one has to put in settings.gradle:

include ':library1'
project(':library1').projectDir = new File('../StickyListHeader/library1')

If you’ve done this correctly, you’ll notice that the modules referenced by your project will show up in the project navigator, even if those modules are external to the project directory:

This allows you to work on library code and app code simultaneously. Version control integration also works just fine when you reference modules externally this way. You can commit and push your modifications to the library code just like you can commit and push modifications to your app code.

This way of setting up multiple projects avoids the difficulties that plague Google’s recommended configuration. Because we are referencing a module that is outside of the project directory we don’t have to make extra copies of the library module for every app that depends on it and we can version our libraries without any sort of git submodule nonsense.

Unfortunately, this other way of setting up multiple projects is very difficult to find. Obviously, its not something you’ll figure out from looking at Google’s guide, and at this point, there’s no way to configure your projects in this way by using the UI of Android Studio.

Documentation Way

This is the recommended way as per the advice given in the Android Studio documentation.

Create a library module

Create a new project to make your library in. Click File > New > New Module > Android Library > Next > (choose name) > Finish. Then add whatever classes and resourced you want to your library.

When you build the module an AAR file will be created. You can find it in project-name/module-name/build/outputs/aar/.

Add your library as a dependency

You can add your library as a dependency to another project like this:

1. Import your library AAR file with File > New Module > Import .JAR/.AAR Package > Next > (choose file location) > Finish. (Don't import the code, otherwise it will be editable in too many places.)

2. In the settings.gradle file, make sure your library name is there.

   include ':app', ':my-library-module'
   

3. In the app's build.gradle file, add the compile line to the dependencies section:

   dependencies {
       compile project(":my-library-module")
   }
   

4. You will be prompted to sync your project with gradle. Do it.

That's it. You should be able to use your library now.

Notes

If you want to make your library easily available to a larger audience, consider using JitPac or JCenter.

In my case, using MAC OS X 10.11 and Android 2.0, and by doing exactly what Aqib Mumtaz has explained.

But, each time, I had this message : "A problem occurred configuring project ':app'. > Cannot evaluate module xxx : Configuration with name 'default' not found."

I found that the reason of this message is that Android 2.0 doesn't allow to create a library directly. So, I have decided first to create an app projet and then to modify the build.gradle in order to transform it as a library.

This solution doesn't work, because a Library project is very different than an app project.

So, I have resolved my problem like this :

• First create an standard app (if needed) ;
• Then choose 'File/Create Module'
• Go to the finder and move the folder of the module freshly created in your framework directory

Then continue with the solution proposed by Aqib Mumtaz.

As a result, your library source will be shared without needing to duplicate source files each time (it was an heresy for me!)

Hoping that this help you.

There are two simplest ways if one does not work please try the other one.

1. Add dependency of the library inside dependency inside build.gradle file of the library u r using, and paste ur library in External Libraries.

OR

2. Just Go to your libs folder inside app folder and paste all your .jar e.g Library files there Now the trick here is that now go inside settings.gradle file now add this line "include ':app:libs'" after "include ':app'" It will definitely work...........:)

You can add a new module to any application as Blundell says on his answer and then reference it from any other application.

If you want to move the module to any place on your computer just move the module folder (modules are completely independent), then you will have to reference the module.

To reference this module you should:

• On build.gradle file of your app add:

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

• On settings.gradle file add the following:

   include ':app', ':myandroidlib'
   project(':myandroidlib').projectDir = new File(PATH_TO_YOUR_MODULE)
  

Don't forget to use apply plugin: 'com.android.library' in your build.gradle instead of apply plugin: 'com.android.application'

As theczechsensation comment above I try to search about Gradle Build Varians and I found this link: http://code.tutsplus.com/tutorials/using-gradle-build-variants--cms-25005 This is a very simple solution. This is what I did: - In build.gradle:

flavorDimensions "version"

productFlavors {
    trial{
        applicationId "org.de_studio.recentappswitcher.trial"
        flavorDimension "version"
    }
    pro{
        applicationId "org.de_studio.recentappswitcher.pro"
        flavorDimension "version"
    }

}

Then I have 2 more version of my app: pro and trial with 2 diffrent packageName which is 2 applicationId in above code so I can upload both to Google Play. I still just code in the "main" section and use the getpackageName to switch between to version. Just go to the link I gave for detail.

Had the same question and solved it the following way:

Start situation:

FrigoShare (root)
|-Modules:    frigoshare,   frigoShare-backend

Target: want to add a module named dataformats

1. Add a new module (e.g.: Java Library)

2. Make sure your settings.gradle look like this (normally automatically):

   include ':frigoshare', ':frigoShare-backend', ':dataformats'

3. Make sure (manually) that the build.gradle files of the modules that need to use your library have the following dependency:

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

Check out this link about multi project setups.

Some things to point out, make sure you have your settings.gradle updated to reference both the app and library modules.

settings.gradle: include ':app', ':libraries:lib1', ':libraries:lib2'

Also make sure that the app's build.gradle has the followng:

dependencies {
     compile project(':libraries:lib1')
}

You should have the following structure:

 MyProject/
  | settings.gradle
  + app/
    | build.gradle
  + libraries/
    + lib1/
       | build.gradle
    + lib2/
       | build.gradle

The app's build.gradle should use the com.android.application plugin while any libraries' build.gradle should use the com.android.library plugin.

The Android Studio IDE should update if you're able to build from the command line with this setup.