Learn How To Add Expansion Files In Android?

As every Android developer knows that it is not possible to launch an Android app with a size greater than 100 MB on the store, this is something each developer should retain while developing an application with a large number of assets. As assets grow we look for more reliable techniques to optimize the application like using a WebP image instead of PNG or adding SVG (Vector Drawable) or eliminating unwanted resources.

Some applications demand dynamic graphics or media files or huge assets. The Android team had provided an option of expansion support. Let’s see how to implement an App expansion for an application.

Expansion Files And It’s File Type

Expansion files are utterly archived files format as Opaque Binary Blob (.obb) which we can upload once the released APK is updated on Google Play Console. There are two distinct expansion file alternatives provided by Google Android Team. Each file has a volume of around 2GB and is of any format ZIP, PDF or MP4 that can be shared.

  1. Main Expansion File is a primary alternative for additional resources required by an application.
  2. Patch Expansion File is optional and has small updates to main expansion files.

While we can make use of two alternatives as per requirements, the team has recommended making use of the Main Expansion file to deliver a primary app asset through them, and patch files should be used rarely for frequent updates.

OBB File Format

We can upload any format (MP4, ZIP, PDF) expansion file. Regardless of the uploaded file format, the Play Console will always consider them as Opaque Binary Blob (OBB). The file can be renamed in the below format

[main/patch].<expansion-version>.<package-name>.obb

main: Specifies the file is the main file or primary

patch: Associated file for a small update to the primary file

expansion-version: Expansion version indicated the version code of the whole application which should be the same

package-name: The package name symbolizes the name of the application package given in the Android Manifest

For example, if our application version is 1, then it should be defined like this

main.1.com.package_name.obb

OBB Storage Location

When an application with APK expansion is downloaded, the files are instantly stored to the internal shared folder of storage location with an obb folder inside an Android folder.

<shared-storage>/Android/obb/<package-name>/

shared-storage: It is a path to shared storage space.

package-name: The package name symbolizes the name of the application package given in the Android Manifest.

For each android application, there are only single app expansion files, while the other is a patch file that supports frequent updates to main files.

Implementing Expansion File In Android

The fundamental logic is to download the Expansion file while installing an application from the Play Store. Even so, we need to add the various dependencies in the application code which will help to download the expansion file from the store.

The first and leading thing is to head toward the SDK manager and go-to tab SDK tools and download the Google Play APK Expansion Library and Google Play Licensing Library. Please see the below image

Implementing Expansion Files In Android | MindBowser
Fig 1.1 Library Dependency

The Down-loader Library

To use expansion in the application we need to import the Downloader Library as a new module. It is present inside the Android SDK under the extra package folder. Which further goes up to extras > google > market_apk_expansion > downloader_library.

Follow the below steps for adding a library to the project:

  1. Before continuing the library go-to project.properties files and remove/comment out the line

“android.library.reference.1=../market_licensing.”

  1. File > New > New Import
  2. Browse to the downloader_library folder, press open, and import.

Market Licensing Library

The second step is to import the market licensing library from the Android SDK folder.

Follow the below steps for adding a library to the project:

  1. File > New > New Module
  1. Browse to /extras/google/market_licensing/library/ folder.
  2. Rename Module name from library to market_licensing and import it in the project.

Import zip library

This library implementation is optional. If an expansion file is in a zip package this library can be useful.

Follow the below steps for adding a library to the project:

  1. File > New > New Imports
  2. Browse to zip_files inside the SDK extras folder
  3. Import the library.
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Conclusion 

This article is helpful for understanding expansion files that help in creating gaming applications or applications having requirements of larger size images, videos or pdf files into it. We have to add the obb file created to the play console while launching the application on the play store.

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