大型App面臨的挑戰

- Multidex探究與Apk size最佳化

2016/04/21 @ Android Taipei

Hello!I am Johnny Lee

Software Engineer at XPEC, HTC and Leopard MobileYou can find me at facebook.com/johnnnielee

Outline● Multidex● 衍生應用

○ Compressing sub-dex○ Install dex in worker thread

● Tips for reducing APK file size

Multidex

Single Dex methods over 65536

will cause

“Conversion to Dalvik format failed”

at build time

Single Dex file size >5MB

will cause

INSTALL_FAILED_DEXOPT

before Android 2.3 at apk install time

“Multidex build tools construct a primary dex (classes.dex) and supporting (classes2.dex, classes3.dex) as needed. The build system will then package them into an APK file for distribution.

-Android Developer

What is dex file?

Java code → Java bytecode → Dalvik executable (DEX)

“Programs are commonly written in Java and compiled to bytecode for the Java virtual machine, which is then translated to Dalvik bytecode and stored in .dex (Dalvik EXecutable).

-Wikipedia

How to use it?

STEP1: Change your Gradle build

configuration to enable multidex

Below Android 5.0

STEP2: Making application extends MultiDexApplication

Prior to Android 5.0

“Android 5.0 and higher uses a runtime called ART which natively supports loading multiple dex files from application APK files. ART scans for classes(..N).dex files and compiles them into a single .oat file at install time.

-Android Developer

For Android 5.0 and higher

身為一個專業的Android工程師...

What’s the secret behind

Multidex.install()?

● What’s the rule to divide dex into primary dex and sub dex?

● How to install dex at runtime?

Primary dex should contain all classes have been referenced before Mutidex.install() was called

Multidex.install()

● What’s the rule to divide dex into primary dex and sub dex?

● How to install dex at runtime?

1. Call DexPathList$makeDexElement() by reflection to force Dalvik loads dex files

2. Get dexElements by reflection and write back extra elements by System.arraycopy()

衍生應用

● Reducing APK size by compressing sub-dex

● Show splash activity before install sub-dex

● Inject compress dex task into build.gradle○ Unpack Proguarded jar to get class files○ Split class files into main-dex and sub-dexs.○ Generate dex file from class file by “dx” build tool○ Compress sub-dex files by lzma○ Add compressed files into resource file

8.64MB→ 7.79MB

● Modify Multidex.install()○ Decompress zipped sub-dex○ Install sub-dex

● Reducing APK size by compressing sub-dex

● Show splash activity before install sub-dex

● Defer install sub-dex process into worker thread

● Move splash activity related classes into maindex

● Show splash activity

Before After

Other tips for reducing APK file size

● Resource Proguard(link)

○ Obfuscate resources id in APK■ res/drawable/logo.png → r/s/a.png■ Reduce resource table size in Resources.arsc

○ Repack Resources.arsc by 7-zip

● IconFont(link)

○ Merge multiple SVGs into one TTF

● TinyPNG(link)

○ Reduce PNG size by decreasing the number of colors in the image

Thanks!Any questions?You can find me at facebook.com/johnnnielee