If you want to enable Travis builds for your project, you first need to log in to Travis CI and connect your account to GitHub. Once that is done, you need to enable the project you want to build in the settings.

In order to configure the build process, Travis requires you to create a file called .travis.yml that contains the entire setup. To configure an Android project, you need to define the language and add a few Android-specific properties:

language: android
android:
  components:
    # The build tools version used by your project
    - build-tools-22.0.1

    # The SDK version used to compile your project
    - android-22

    # Additional components
    - extra-android-m2repository

The language setting specifies which kind of build process you want to run. In this case, you are building an Android app. The Android-specific properties include the version of the build tools and the Android SDK version that need to be used. Travis will download those prior to running the build tasks. If you make use of the support library or Google Play Services, you need to specify that explicitly because Travis needs to download the repositories for those dependencies as well.

If you create an Android project on Microsoft Windows, the Gradle Wrapper file is known to have issues with permissions. Therefore, it is a good idea to fix the permission before running the actual build script. You can add a prebuild step like this:

before_script:
  # Change Gradle wrapper permissions
  - chmod +x gradlew

To start the build itself, add this line to the Travis configuration file:

# Let's build
script: ./gradlew clean build

This command will run the Gradle Wrapper, just like you would on a developer machine, and execute the clean and build tasks.

When you are done configuring the Travis build, you can commit and push the file to the project's GitHub repository. If everything is set up correctly, Travis will start the build process, which you can follow on the Travis website. This is what it looks like when a project is successfully built:

Travis also sends an e-mail report after every build. This can be especially useful if you are the maintainer of an open source library that regularly gets pull requests. The report e-mail from Travis looks like this when a build is successful:

You will quickly notice that Travis has a big downside, and that is speed. Travis does not give you one specific machine, but boots up a vanilla virtual machine for every build you trigger. This means for every new build, Travis has to download and install the Android SDK and build tools, before it can start building your app or library.

On the upside, Travis is free and public, which makes it perfect for open source projects. Travis also builds pull requests automatically, which can give you peace of mind when someone submits a patch to your code.