Android application package

Android Package (APK)[1] is the package file format used by the Android, and a number of other Android-based operating systems for distribution and installation of mobile apps, mobile games and middleware.

APK
Filename extension.apk, .xapk
Internet media type
application/vnd.android.package-archive
Type of formatPackage format
Container forMobile apps
Extended fromJAR

APK is analogous to other software packages such as APPX in Microsoft Windows or a Debian package in Debian-based operating systems. To make an APK file, a program for Android is first compiled using Android Studio[2], and then all of its parts are packaged into one container file. An APK file contains all of a program's code (such as .dex files), resources, assets, certificates, and manifest file. As is the case with many file formats, APK files can have any name needed, but it may be required that the file name ends in the file extension ".apk" for being recognized as such.[3][4][5][6]

The Android system allows users to manually install APK files only after they turn on an "Unknown Sources" setting that allows installation from sources other than trusted ones like Google Play. One may do so for many reasons, such as to install apps not found on the store, or to install an older version.[7] Although one can downgrade an app this way by uninstalling the new version first, doing it via Android Debug Bridge is better as it allows for keeping data.[8]

Package contents

An APK file is an archive that usually contains the following files and directories:

  • META-INF directory:
    • MANIFEST.MF: the Manifest file
    • The certificate of the application.
    • CERT.SF: The list of resources and a SHA-1 digest of the corresponding lines in the MANIFEST.MF file; for example:
      Signature-Version: 1.0
Created-By: 1.0 (Android)
SHA1-Digest-Manifest: wxqnEAI0UA5nO5QJ8CGMwjkGGWE=
...
Name: res/layout/exchange_component_back_bottom.xml
SHA1-Digest: eACjMjESj7Zkf0cBFTZ0nqWrt7w=
Name: res/drawable-hdpi/icon.png
SHA1-Digest: DGEqylP8W0n0iV/ZzBx3MW0WGCA=
  • lib: the directory containing the compiled code that is platform dependent; the directory is split into more directories within it:
    • armeabi: compiled code for all ARM based processors only
    • armeabi-v7a: compiled code for all ARMv7 and above based processors only
    • arm64-v8a: compiled code for all ARMv8 arm64 and above based processors only[9]
    • x86: compiled code for x86 processors only
    • x86_64: compiled code for x86 64 processors only
    • mips: compiled code for MIPS processors only
  • res: the directory containing resources not compiled into resources.arsc (see below).
  • assets: a directory containing applications assets, which can be retrieved by AssetManager.
  • AndroidManifest.xml: An additional Android manifest file, describing the name, version, access rights, referenced library files for the application. This file may be in Android binary XML that can be converted into human-readable plaintext XML with tools such as AXMLPrinter2, apktool, or Androguard.
  • classes.dex: The classes compiled in the dex file format understandable by the Dalvik virtual machine and by the Android Runtime.
  • resources.arsc: a file containing precompiled resources, such as binary XML for example.

See also

References
  1. "Application Fundamentals | Android Developers". Android Developers. Retrieved 2018-12-03.
  2. "Application Studio | Android Studio". Android Developers.
  3. "Inside the Android Application Framework" (video). Google Sites. 2008.
  4. Hatem Ben Yacoub (20 April 2018). "Tips: How to install apk files on Android Emulator". Open Ha Magazine. Archived from the original on 2012-05-26.
  5. "The Structure of Android Package (APK) Files". OPhone SDN. OPhone Software Developer Network. 17 November 2010. Archived from the original on 8 February 2011.
  6. chibucks (28 May 2010). "Learn to Fish: General Structure of an APK". SDX-Developers Forum. Simple Machines Forum. Archived from the original on 17 July 2012.
  7. "Unknown Sources: Everything you need to know!". Android Central. 27 July 2018.
  8. "How to Downgrade an App on Android - No Root Needed". xda-developers. 25 August 2017.
  9. "ABI Management | Android Developers". developer.android.com. Retrieved 16 June 2018.
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