The Road To Single Dex (GDG San Francisco Meetup)

Jared Burrows
The Road to Single
Dex
Jared Burrows

Motivation
• Yammer is a social networking service used for
communication within an organization
• 3 APKs: Min SDK 15, 16 and 19, Target SDK 26
• Loading extra DEX ﬁles may lead to possible ANRs
• Multidex makes very large memory allocation requests may
crash during run time

Focus
• Reducing DEX method count
• Reducing APK size

Results
1 DEX ﬁle, Smaller APK, All features kept!
Before After Reduction
Method Count 85k+ 60.8k 28.47%
APK Size 10.7MB+ 7.1MB 33.64%

What makes an APK so big?
 
Multiple DEX ﬁles
+
Many Resources

What is inside an APK?
• AndroidManifest.xml
• assets/
• classes.dex
• META-INF/ 
- CERT.SF 
- MANIFEST.MF 
- CERT.RSA
• lib/
• res/ 
- drawable/ 
- layout/
• resources.arsc

Big APKs - DEX size
• Remove all/any dead code
• Remove any old/unused libraries
• Refactor out large/non-mobile libraries
• Verify Gradle conﬁgurations

Big APKs - Resources
• Remove extra and unused ﬁles in your “/res” folder
• Remove extra and used ﬁles in your “/assets” folder

Before Optimizations - Debug build
$ gradlew countDebugDexMethods sizeDebugApk 
 
> Task :countDebugDexMethods 
Total methods in debug.apk: 113007 (172.44% used)  
Total ﬁelds in debug.apk: 50547 (77.13% used)  
Methods remaining in debug.apk: 0  
Fields remaining in debug.apk: 14988 
 
> Task :sizeDebugApk 
Total APK Size in debug.apk in bytes: 12386152 (12.3MB)

Before Optimizations - Release build
$ gradlew countReleaseDexMethods sizeReleaseApk (with Proguard) 
 
> Task :countReleaseDexMethods 
Total methods in release.apk: 85259 (130.10% used)  
Total ﬁelds in release.apk: 39887 (60.86% used)  
Methods remaining in release.apk: 0  
Fields remaining in release.apk: 25648 
 
> Task :sizeReleaseApk 
Total APK Size in release.apk in bytes: 10764242 (10.7MB)

Baselined Results
85k+ > 64k DEX limit = 2 DEX ﬁles
Debug Release
Method Count 113k+ 85k+
APK Size 12.3MB+ 10.7MB+

Trimming the DEX size - Dead Code
• Remove any and all unused code 
- PMD - Comes with Gradle 
- Proguard - Comes with Android Gradle Plugin 
- Intellij/Android Studio Inspections - Click “Analyze” > Click “Inspect Code…”
• Remove all unused libraries 
- We chose HockeyApp over an open source analytics library called ApplicationInsights 
- HockeyApp’s functionality encompasses all of the functionality that we need from
ApplicationInsights

Trimming the DEX size - Old Libraries
• Remove old libraries 
- Using HockeyApp for releasing versioning/nightlies - Allowed us to remove AndroidQuery - version
checking
• Remove unnecessary libraries 
- Try not add libraries that duplicate Android’s existing functionality 
- Able to remove Apache Commons validator - validate emails addresses
• Removing differential versions of same library 
- Jackson 1 and Jackson 2 are the same library but Jackson 2 has a different package name 
- Duplicating functionality across across prevent tools such as Proguard from optimizing

Trimming the DEX size - Transitive Libraries
• Watch out for Library Duplication 
- Jackson 1 vs Jackson 2 vs Gson 
- Consider using a Groovy map in your build.gradle
• Bringing in extra libraries based on a libraries’ dependencies 
- Use “gradlew dependencies” to see what you are actually using

ext { 
supportLibraryVersion = "27.0.0" 
} 
 
ext.deps = [ 
"design" : "com.android.support:design:$supportLibraryVersion", 
"recyclerviewV7" : "com.android.support:recyclerview-v7:$supportLibraryVersion", 
"appcompatV7" : "com.android.support:appcompat-v7:$supportLibraryVersion", 
"cardviewV7" : "com.android.support:cardview-v7:$supportLibraryVersion" 
]
dependencies { 
compile deps.design 
}
Keep track of dependencies, Enforce versions

gradlew dependencies --conﬁguration compile*
compile - Classpath for compiling the main sources.
+--- project :yammer-common
| --- com.google.code.gson:gson:2.8.2
+--- project :yammer-data
| --- com.squareup.retrofit:retrofit:1.9.0
| --- com.google.code.gson:gson:2.3.1 -> 2.8.2
+--- com.microsoft.aad:adal:1.12.0
| --- com.google.code.gson:gson:2.2.4 -> 2.8.2

Trimming the DEX size - Large Libraries
• Try not to use Large/Non-mobile libraries 
- Guava - 15k+ methods 
- Jackson2 2.9.0.pr3 - 12k+ methods 
- Check size of libraries with methodscount.com
• Necessary Evils 
- AppCompat - 25.4.0 has 16.5k+ methods, 26.0.0-beta2 has 18.3k+ (continues to increase) 
- Google Play Services GCM 11.0.0 - 16.7k+ methods 
- Simply using both App Compat + Play Services together brings your APK to 30k+ methods,
halfway to the 64k limit per DEX ﬁle!

Trimming the DEX size - MethodsCount
methodscount.com/?lib=com.android.support:appcompat-v7:24.2.1

Trimming the DEX size - Gradle Conﬁgurations
dependencies {
compile project(":common") 
compile project(":common-test") 
}
Pre Android Gradle Plugin 3.0

Pre Android Gradle Plugin 3.0
dependencies {
compile project(":common") 
testCompile project(":common-test") 
}

dependencies {
implementation project(":common") 
testImplementation project(":common-test") 
}
With Android Gradle Plugin 3.0

Trimming the DEX size - Proguard
• Use Proguard on Release builds 
- Set “minifyEnabled” to true! 
- Easiest way to help lower your DEX size
• Consider using “proguard-android-optimize.txt” over
“proguard-android.txt” 
- Proguard will make 5 optimization passes on your code

android { 
buildTypes { 
release { 
minifyEnabled true 
proguardFile getDefaultProguardFile("proguard-android.txt") 
proguardFile "custom-proguard-rules.txt" 
signingConfig signingConfigs.release 
} 
} 
} 
Make sure you turn on “minifyEnabled”

Make sure you provide Proguard rules
android { 
buildTypes { 
release { 
proguardFile getDefaultProguardFile("proguard-android.txt") 
} 
} 
}

Try using more aggressive Proguard rules
android { 
buildTypes { 
release { 
proguardFile getDefaultProguardFile("proguard-android-optimize.txt") 
} 
} 
}

• Remove extra Proguard rules
• Keep them up to date with the current libraries in your app
• Make sure to use “-keep” sparingly

Over using “-keep” can be costly
-keep class okhttp3.* { ; } 
-keep interface okhttp3.* { ; } 
-dontwarn okhttp3.** 
-dontnote okhttp3.**

Try and let Proguard decide
-dontwarn okhttp3.** 
-dontnote okhttp3.**

Trimming the Resources - Lint
• Make sure to use lint to check for “UnusedResources”
• Do not suppress this lint rule unless you are writing an
Android library
• Consider failing the builds based on lint warnings/errors

Strict lint options
android { 
lintOptions { 
textReport true 
textOutput "stdout" 
checkAllWarnings true 
warningsAsErrors true 
} 
}

android { 
lintOptions { 
error "UnusedResources" 
} 
}
Less strict, check for “UnusedResources”

Trimming the Resources - ShrinkResources
• What Lint does not find, you have to remove manually
• Remove all unused resources in “assets/” folder 
- Raw media such as Font files
• Use “shrinkResources” to remove unused resources 
- Great for removing library dependencies resources in your final APK

android { 
buildTypes { 
release { 
} 
} 
} 
Missing “shrinkResources”

Added “shrinkResources”
android { 
buildTypes { 
release { 
minifyEnabled true
shrinkResources true 
} 
} 
}

Using “shrinkResources”
android { 
buildTypes { 
release { 
minifyEnabled true
shrinkResources true 
} 
} 
}

Trimming the Resources - ResConfigs
• Use “resConfigs” to filter out localizations that you do not
want/support in your app

Trimming the Resources - ResConﬁg
Using “resConﬁgs” to keep multiple resources or languages
android {
defaultConfig {
resConfigs "en"
}
}

Trimming the Resources - ResConﬁg
Using “resConﬁgs” to keep multiple languages
android {
defaultConfig { 
resConfigs "en","de","fr" 
} 
}

Trimming the Resources - PackagingOptions
• Remove extra files that are baked into your APK
• Use the APK Analyzer to find these files 
- In Android Studio, Click “Build” > Click “Analyze APK…”
• Use “packagingOptions” to filter out these files

android { 
packagingOptions { 
exclude "META-INF/LICENSE.txt" 
exclude "META-INF/NOTICE.txt" 
} 
}
Common “packagingOptions” excludes

After using common “packagingOptions” excludes

Strict “packagingOptions” excludes
android { 
packagingOptions { 
exclude "**/*.kotlin_module"
exclude "**/*.version" 
exclude "**/kotlin/**" 
exclude "**/*.xml" 
exclude “**/*.txt"
exclude "**/*.properties" 
} 
}

After using stricter “packagingOptions” excludes

Trimming the Resources - Vector Drawables
• Consider converting simple PNGs to “Vector” Drawables
• Single XML ﬁle is smaller than multiple PNGs
• Use tools such as “svg2android” to convert SVGs to Android
Vector Drawables

android { 
defaultConfig { 
resConfigs "en", "de", "fr" 
vectorDrawables { 
useSupportLibrary = true 
} 
} 
}
Using “vectorDrawables.useSupportLibrary = true” to prevent PNG generation

inloop.github.io/svg2android/

After dropping your SVG ﬁle, Copy it to your project in “res/drawable”

Make sure to use “app:srcCompat” your in XML
<?xml version="1.0" encoding="utf-8"?> 
<LinearLayout 
xmlns:android="http://schemas.android.com/apk/res/android" 
xmlns:app="http://schemas.android.com/apk/res-auto" 
android:orientation="vertical" 
android:layout_width="match_parent" 
android:layout_height="match_parent"> 
 
<ImageView 
android:layout_width="30dp" 
android:layout_height="30dp" 
android:src="@drawable/circle"/> 
 
<ImageView 
android:src="@drawable/hello"/> 
</LinearLayout>

Using “app:srcCompat” your in XML
<?xml version="1.0" encoding="utf-8"?> 
<LinearLayout 
xmlns:android="http://schemas.android.com/apk/res/android" 
xmlns:app="http://schemas.android.com/apk/res-auto" 
android:orientation="vertical" 
android:layout_width="match_parent" 
android:layout_height="match_parent"> 
 
<ImageView 
app:srcCompat="@drawable/circle"/> 
 
<ImageView 
app:srcCompat="@drawable/hello"/> 
</LinearLayout>

Trimming the Resources - WebP
• Reduces image sizes by converting to WebP
• Does not need to compress at build time(PNG crunching)
• By converting beforehand, this will help speed up your build

Trimming the Resources - WebP
Right-click on “drawable” folders, click on “Convert to WebP”

After Optimizations - Debug build
$ gradlew countDebugDexMethods sizeDebugApk 
 
> Task :countDebugDexMethods 
Total methods in debug.apk: 100595 (153.50% used)  
Total ﬁelds in debug.apk: 51278 (78.25% used)  
Methods remaining in debug.apk: 0  
Fields remaining in debug.apk: 14257 
 
> Task :sizeDebugApk 
Total APK Size in debug.apk in bytes: 10053036 (10.1MB)

After Optimizations - Release build
$ gradlew countReleaseDexMethods sizeReleaseApk (with Proguard) 
 
> Task :countReleaseDexMethods 
Total methods in release.apk: 60810 (92.79% used)  
Total ﬁelds in release.apk: 29445 (44.93% used)  
Methods remaining in release.apk: 4725 
Fields remaining in release.apk: 36090 
 
> Task :sizeReleaseApk 
Total APK Size in release.apk in bytes: 7049930 (7.1MB)

Optimized Results
60.8k+ < 64k DEX limit = 1 DEX ﬁle!
Debug Release
Method Count 100k+ 60.8k
APK Size 10.1MB+ 7.1MB

Before vs After Release Builds
1 DEX ﬁle, Smaller APK, All features kept!
Before After Reduction
Method Count 85k+ 60.8k 28.47%
APK Size 10.7MB+ 7.1MB 33.64%

Automating Dex Count Plugin
gradle.taskGraph.whenReady { taskGraph -> 
if (taskGraph.hasTask(":assembleRelease")) { 
dexcount { 
maxMethodCount = 61000 // 61k methods 
} 
} 
}
github.com/KeepSafe/dexcount-gradle-plugin

Automating APK Size Plugin
gradle.taskGraph.whenReady { taskGraph -> 
if (taskGraph.hasTask(":assembleRelease")) { 
apkSize { 
maxApkSize = 8000 // in Kb 
} 
} 
}
github.com/vanniktech/gradle-android-apk-size-plugin

Thank you! Questions?
twitter.com/jaredsburrows
github.com/jaredsburrows
jaredsburrows@gmail.com
jaredsburrows.com

The Road To Single Dex (GDG San Francisco Meetup)

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