The document discusses various techniques for reducing Android application size, including compressing resources and assets, trimming unused resources and assets, splitting APK files, shrinking libraries, shrinking the application bytecode, and splitting dex files. It provides examples of using tools like ProGuard, DexGuard, and the Android Gradle plugin to apply these techniques at build time in order to reduce the overall size of the packaged Android application.

1. Fighting application size
with ProGuard and beyond
Eric Lafortune
Developer of ProGuard and DexGuard
Technical director at Saikoa
www.saikoa.com

2. Applications
Dalvik
bytecode
Resources Assets
Native
code
Renderscript
code
App

3. Dalvik
bytecode
Resources Assets
Native
code
Renderscript
code
Technical constraints
App
Google Play Store: max 50 MB
Froyo/Gingerbread: 5 MB LinearAlloc buffer
Dex format: max 65536 method IDs

4. Android build process

5. Android build process
Application
Java bytecode
Libraries
Java bytecode
Dex Dalvik bytecode
Javac
Application
Java source
Libraries
Java bytecode
XML resources
Assets Assets
Compiled
XML resourcesAapt

6. Compress media
●
Images: JPEG (lossy)
●
Images: PNG
●
Audio: AAC
●
Video: H264 AVC
aapt crunch -S input_dir -C output_diraapt crunch -S input_dir -C output_dir

7. Remove unused resources
●
Lint (Android SDK)
●
android-resource-remover (Philipp Berner)
●
android-unused-resources (S. Kennedy)
●
Gradle (Android SDK)
gradle lintgradle lint
android {
buildTypes {
release {
minifyEnabled true
shrinkResources true
}
}
}
android {
buildTypes {
release {
minifyEnabled true
shrinkResources true
}
}
}

8. Splitting apk files

9. Splitting apk files
Application
Java bytecode
Libraries
Java bytecode
Dex Dalvik bytecode
Javac
Application
Java source
Libraries
Java bytecode
XML resources
Assets
Assets
Compiled
XML resources
Aapt
Dalvik bytecode
Assets
Compiled
XML resources

10. Splitting apk files
●
Different variants in Gradle:
android {
...
productFlavors {
flavor1 {
ignoreAssetsPattern '!*_large.png'
assets.srcDirs = ['assets1']
res.srcDirs = ['res1']
}
flavor2 {
ignoreAssetsPattern '!*_small.png'
assets.srcDirs = ['assets2']
res.srcDirs = ['res2']
}
}
}
android {
...
productFlavors {
flavor1 {
ignoreAssetsPattern '!*_large.png'
assets.srcDirs = ['assets1']
res.srcDirs = ['res1']
}
flavor2 {
ignoreAssetsPattern '!*_small.png'
assets.srcDirs = ['assets2']
res.srcDirs = ['res2']
}
}
}

11. Splitting apk files
●
Splits in Gradle:
android {
...
splits {
density {
enable true
reset()
include 'mdpi', 'hdpi', 'xhdpi'
}
abi {
enable true
reset()
include 'armeabi-v7a', 'x86', 'mips'
}
}
}
android {
...
splits {
density {
enable true
reset()
include 'mdpi', 'hdpi', 'xhdpi'
}
abi {
enable true
reset()
include 'armeabi-v7a', 'x86', 'mips'
}
}
}

12. Code size

13. Code size
Application
Java bytecode
Libraries
Java bytecode
Dex Dalvik bytecode
Javac
Application
Java source
Libraries
Java bytecode
XML resources
Assets Assets
Compiled
XML resourcesAapt
java.lang.IllegalArgumentException:
method ID not in [0, 0xffff]: 65536
java.lang.IllegalArgumentException:
method ID not in [0, 0xffff]: 65536

14. Dex file
...
Strings
Types
Prototypes
Field IDs
Method IDs
Class definitions
Method IDs
#0: Accounts . <init>(.....)
#1: AccountManager . get(......)
#2: AccountManager . …..
#3: …..
#4: …..
...
...
...
...
...
...
...
...
...
...
...
...
...
...
#65535: …..

15. ProGuard
Shrink
Android
runtime
Optimize Obfuscate
Android
runtime
Libraries
Application
code
Processed
code

16. ProGuard
Application
Java bytecode
ProGuard
Libraries
Java bytecode
Processed
Java bytecode Dex
Javac
Application
Java source
Libraries
Java bytecode
XML resources
Assets Assets
Compiled
XML resourcesAapt
Dalvik bytecode

17. -keepclassmembers,allowobfuscation class * {
@dagger.** <fields>;
@dagger.** <methods>;
}
-keep class **$$ModuleAdapter
-keep class **$$InjectAdapter
-keep class **$$StaticInjection
-keep class com.example.DemoModule
-keep class com.example.AndroidModule
-keep class com.example.HomeActivity
-keepnames class dagger.Lazy
-keepclassmembers,allowobfuscation class * {
@dagger.** <fields>;
@dagger.** <methods>;
}
-keep class **$$ModuleAdapter
-keep class **$$InjectAdapter
-keep class **$$StaticInjection
-keep class com.example.DemoModule
-keep class com.example.AndroidModule
-keep class com.example.HomeActivity
-keepnames class dagger.Lazy
Example configuration: Dagger
Generated classes
Corresponding base classes

18. Libraries
Library Method IDs
Google Play Services 6.0 23,607
Guava 15.0 14,495
Yahoo Flurry Ads 4.1.0 8,511
ActionBarSherlock 4.4.0 4,300
RoboGuice 2.0 3,787
Facebook 3.5.2 3,166
Yahoo Flurry Analytics 4.1.0 1,148
Scala Core 2.11.2 50,786

19. ProGuard on libraries
ProGuard
Library
Java bytecode
Processed library
Java bytecode

20. Shrink Ads library
-injars google-play-services.jar
-outjars google-play-services-ads.jar
-libraryjars android-sdk/extras/android/support/v4/android-support-v4.jar
-libraryjars android-sdk/platforms/android-20/android.jar
-dontoptimize
-dontobfuscate
-dontwarn com.google.**.R
-dontwarn com.google.**.R$*
-dontnote
-keep public class com.google.android.gms.ads.** {
public protected *;
}
-keep class com.google.android.gms.common.internal.safeparcel.SafeParcelable {
java.lang.String NULL;
}
-injars google-play-services.jar
-outjars google-play-services-ads.jar
-libraryjars android-sdk/extras/android/support/v4/android-support-v4.jar
-libraryjars android-sdk/platforms/android-20/android.jar
-dontoptimize
-dontobfuscate
-dontwarn com.google.**.R
-dontwarn com.google.**.R$*
-dontnote
-keep public class com.google.android.gms.ads.** {
public protected *;
}
-keep class com.google.android.gms.common.internal.safeparcel.SafeParcelable {
java.lang.String NULL;
}
proguard @ configuration.txtproguard @ configuration.txt
Command line:
configuration.txt

21. Shrink Ads library
Before After Reduction
Size 3.3 M 578 K 83 %
Classes 3294 497 85 %
Method IDs 23607 3751 84 %
ProGuard
Google Play
Services
library
Ads library

22. Shrink Maps library
-injars google-play-services.jar
-outjars google-play-services-maps.jar
-libraryjars android-sdk/extras/android/support/v4/android-support-v4.jar
-libraryjars android-sdk/platforms/android-20/android.jar
-dontoptimize
-dontobfuscate
-dontwarn com.google.**.R
-dontwarn com.google.**.R$*
-dontnote
-keep public class com.google.android.gms.maps.**,
com.google.android.gms.common.**,
com.google.android.gms.location.** {
public protected *;
}
-keep class com.google.android.gms.common.internal.safeparcel.SafeParcelable {
java.lang.String NULL;
}
-injars google-play-services.jar
-outjars google-play-services-maps.jar
-libraryjars android-sdk/extras/android/support/v4/android-support-v4.jar
-libraryjars android-sdk/platforms/android-20/android.jar
-dontoptimize
-dontobfuscate
-dontwarn com.google.**.R
-dontwarn com.google.**.R$*
-dontnote
-keep public class com.google.android.gms.maps.**,
com.google.android.gms.common.**,
com.google.android.gms.location.** {
public protected *;
}
-keep class com.google.android.gms.common.internal.safeparcel.SafeParcelable {
java.lang.String NULL;
}
proguard @ configuration.txtproguard @ configuration.txt

23. Shrink Maps library
Before After Reduction
Size 3.3 M 583 K 82 %
Classes 3294 546 83 %
Method IDs 23607 4891 79 %
ProGuard
Google Play
Services
library
Maps library

24. Splitting dex files
Main dex file
Secondary
dex file
Build-time Run-time

25. Splitting dex files
Application
Java bytecode
Libraries
Java bytecode
Dex
Main
Dalvik bytecodeJavac
Application
Java source
Libraries
Java bytecode
XML resources
Assets Assets
Compiled
XML resourcesAapt
Secondary
Dalvik bytecode
Dex

26. Dex splitting: tools
●
secondary-dex-gradle (Mohit Kanwal)
●
Dex 65536 (Mmin18)
●
DexGuard (Saikoa)
●
multiDex (Android Gradle plugin 0.14)

27. Dex splitting: secondary-dex-gradle
●
ApplicationProject
LibraryProject
●
settings.gradle
●
AndroidManifest.xml
●
AppProject/src/com/example/App.java
AppProject/src/com/example/SecondaryDex.java
AppProject/src/com/example/FrameworkHack.java
include ':ApplicationProject', ':LibraryProject'include ':ApplicationProject', ':LibraryProject'
<application
android:name="com.example.App"
... >
<application
android:name="com.example.App"
... >

28. Dex splitting: secondary-dex-gradle
Advantages:
●
It works!
Disadvantages:
●
Split project
●
No references library application→
●
Dex classpath hack

29. Dex splitting: Dex 65536
●
libs/google-play-services.jar (for example)
●
custom_rules.xml
●
AndroidManifest.xml
●
src/com/example/App.java
...
<pathtool
libs="libs/google-play-services.jar"
... />
...
...
<pathtool
libs="libs/google-play-services.jar"
... />
...
<application
android:name="com.example.App"
... >
<application
android:name="com.example.App"
... >
new DexClassLoader(dexFile.getAbsolutePath(),
dexOpt.getAbsolutePath(),
nativeLibraryDir,
classLoader.getParent());
new DexClassLoader(dexFile.getAbsolutePath(),
dexOpt.getAbsolutePath(),
nativeLibraryDir,
classLoader.getParent());

30. Dex splitting: Dex 65536
Advantages:
●
It works!
Disadvantages:
●
Only for library jars
●
Dex classloader hack

31. Dex splitting: DexGuard
●
Gradle, Ant, Eclipse, Maven, Android Studio,...
●
dexguard-project.txt
-splitdexfile com.google.**
-splitdexfile !com.facebook.samples.**, com.facebook.**
-splitdexfile com.google.**
-splitdexfile !com.facebook.samples.**, com.facebook.**

32. Dex splitting: DexGuard
Advantages:
●
Transparent
●
Flexible
●
Lazy loading
Disadvantages:
●
Reflection

33. Dex splitting: multiDex
Android 5.0 loads classes2.dex, classes3.dex, etc.
●
build.gradle
●
AndroidManifest.xml (for legacy platforms)
dependencies {
compile 'com.android.support:multidex:1.0.0'
}
android {
...
defaultConfig {
multiDexEnabled true
}
}
dependencies {
compile 'com.android.support:multidex:1.0.0'
}
android {
...
defaultConfig {
multiDexEnabled true
}
}
<application
android:name="android.support.multidex.MultiDexApplication"
... >
<application
android:name="android.support.multidex.MultiDexApplication"
... >

34. Dex splitting: Android 5.0
Advantages:
●
Latest standard
Disadvantages:
●
Eager loading

35. Summary
Resources and assets:
– Compress
– Trim
– Split apk
Bytecode:
– Shrink libraries
– Shrink application
– Split dex file

36. Further reading
●
“Custom Class Loading in Dalvik”, Fred Chung, Google
http://android-developers.blogspot.com/2011/07/custom-class-loading-in-dalvik.html
●
“Play Services 5.0 Is A Monolith Abomination”, Jake Wharton
http://jakewharton.com/play-services-is-a-monolith/
●
“DEX Sky’s the limit? No, 65K methods is”, Sebastiano Gottardo
https://medium.com/@rotxed/dex-skys-the-limit-no-65k-methods-is-28e6cb40cf71
●
“Multi-dex support”, Xavier Ducrohet
https://plus.google.com/+XavierDucrohet/posts/1FnzwdcBnyC
●
“Under the Hood: Dalvik patch for Facebook for Android”, David Reiss
https://www.facebook.com/notes/facebook-engineering/under-the-hood-dalvik-patch-for-facebook-for-android/10151345597798920
●
“Remove unused resources”, Tor Norbye
https://plus.google.com/+TorNorbye/posts/eHsStybrrBf
●
“Tips for reducing APK file size”, David Karlsson, Sony
http://developer.sonymobile.com/2012/01/31/tips-for-reducing-apk-file-size/

37. Software tools
●
android-resource-remover, Philipp Berner, KeepSafe
https://github.com/KeepSafe/android-resource-remover
●
android-unused-resources, S. Kennedy
https://code.google.com/p/android-unused-resources/
●
secondary-dex-gradle, Mohit Kanwal
https://github.com/creativepsyco/secondary-dex-gradle
●
Dex 65536, Mmin18
https://github.com/mmin18/Dex65536
●
ProGuard
http://proguard.sourceforge.net/
●
DexGuard
http://www.saikoa.com/dexguard

38. Questions?
Open source
Java bytecode
ProGuard
Saikoa
DexGuard
Dalvik bytecode
Shrinking
Optimization