ADVANCED ANDROID APP SHRINKING TECHNIQUES In Search of Lightness: Christophe Beyls bladecoder@androiddev.social

Hello! I am Christophe Beyls Freelance Android developer from Belgium. ▸ bladecoder@androiddev.social ▸ bladecoder.medium.com ▸ github.com/cbeyls 2 Now available for hire!

3 Medium-sized app Large app FOSDEM Companion https://github.com/cbeyls/fosdem-companion-android Tusky https://github.com/tuskyapp/Tusky

Why smaller app packages? ▸ Faster app downloads and less consumed data. (slow connections, costly/limited data fees) ▸ Smaller install size on the device. Uncompressed compiled native code takes more space! ▸ Faster app initialization (less code and resources to load). ▸ Faster performance (code optimizations by R8). 4

Inside an APK file 5 Resources resources.arsc res/ assets/ Bytecode classes.dex classes2.dex … Others AndroidManifest.xml META-INF/ lib/ resources.arsc: Compiled resources tables (strings, colors, dimens, styles, ids, …) res/: Folder containing resource files (images, layouts, menus, fonts, …) assets/ (optional): Folder containing other arbitrary resource files.

6 Android Studio APK Analyzer Browse and explore all file types.

The basics android { buildTypes { release { isMinifyEnabled = true proguardFiles( getDefaultProguardFile("proguard-android.txt"), "proguard-rules.pro" ) isShrinkResources = true } } } 7 build.gradle.kts

The basics android { buildTypes { release { isMinifyEnabled = true proguardFiles( getDefaultProguardFile("proguard-android.txt"), "proguard-rules.pro" ) isShrinkResources = true } } } 8 Remove unused code build.gradle.kts

The basics android { buildTypes { release { isMinifyEnabled = true proguardFiles( getDefaultProguardFile("proguard-android.txt"), "proguard-rules.pro" ) isShrinkResources = true } } } 9 Remove unused resources build.gradle.kts

Agenda 10 1 3 5 6 4 2 Optimize images Optimize dependencies XML resources vs. shrinking Optimize resources Optimize Proguard rules The future: Jetpack Compose

Optimize images Not all pixels are created equal 1

(with comparable perceived image quality) ▸ Replace JPEG with lossy WebP: 20-30% smaller file sizes. ▸ Android 14+ Replace JPEG with AVIF: 50% smaller file sizes. 12 Better lossy image formats

13 640x640 transparent PNG 400,4 Kb 640x640 transparent WebP 106,1 Kb Original Lossy WebP (drawing mode, q98)

14 640x640 transparent PNG 400,4 Kb 640x640 transparent WebP 106,1 Kb Original Lossy WebP (drawing mode, q98)

▸ Replace PNG with lossless WebP: 20-40% smaller file sizes. ▸ For small icons, prefer density-independent Vector Drawables to sets of PNG/WebP images. 15 Better lossless image formats

https://github.com/alexjlockwood/avocado 16 Avocado: optimize vector drawables

Optimize resources Remove, remove, remove 2

Remove unsupported locales ▸ Libraries like AppCompat, Material Components or Google Play Services include many strings in 75+ languages. ▸ Specify the locales you actually support and let the build tool remove the rest. 18 android { defaultConfig { ... resourceConfigurations += listOf("en", "fr", "nl") } } build.gradle.kts

Remove unsupported locales: Example case study 19

Remove unused custom fonts ▸ Each style/weight combination in a font family needs a separate font file. ▸ Not all font variants are used in an app. ▸ The resources shrinker is unable to detect unused variants within a font family. 20

APK meta data 21

Remove APK metadata android { buildTypes { release { packaging { resources { excludes += listOf( "DebugProbesKt.bin", "kotlin-tooling-metadata.json", "/*.properties", "kotlin/**" ) } } vcsInfo.include = false } } dependenciesInfo { includeInApk = false includeInBundle = false } } 22 build.gradle.kts

Remove APK metadata android { buildTypes { release { packaging { resources { excludes += listOf( "DebugProbesKt.bin", "kotlin-tooling-metadata.json", "/*.properties", "kotlin/**" ) } } vcsInfo.include = false } } dependenciesInfo { includeInApk = false includeInBundle = false } } 23 build.gradle.kts For security checks (Google Play only) Version control info

A word about native binaries If ▹ You distribute your app as an APK file ▹ Your app includes large native binaries in the /lib folder Then ▹ You should build one APK file per CPU architecture. 24

APK split per CPU architecture android { splits { abi { isEnable = true reset() include ("x86", "armeabi-v7a", "arm64-v8a") isUniversalApk = false } } } 25 build.gradle.kts

Optimize dependencies Select and deduplicate 3

Your actual dependencies ▸ ./gradlew app:dependencies --configuration releaseCompileClasspath > deps.txt +--- org.jetbrains.kotlinx:kotlinx-coroutines-android:1.8.1 (*) +--- androidx.core:core-ktx:1.13.1 (*) +--- androidx.activity:activity:1.9.0 (*) +--- androidx.fragment:fragment-ktx:1.8.0 | +--- androidx.activity:activity-ktx:1.8.1 -> 1.9.0 | | +--- androidx.activity:activity:1.9.0 (*) | | +--- androidx.core:core-ktx:1.13.0 -> 1.13.1 (*) | | +--- androidx.lifecycle:lifecycle-runtime-ktx:2.6.1 -> 2.8.2 | | | \--- androidx.lifecycle:lifecycle-runtime-ktx-android:2.8.2 | | | +--- androidx.annotation:annotation:1.8.0 (*) | | | +--- androidx.lifecycle:lifecycle-runtime:2.8.2 (*) | | | +--- org.jetbrains.kotlin:kotlin-stdlib:1.8.22 -> 2.0.0 (*) | | | +--- org.jetbrains.kotlinx:kotlinx-coroutines-android:1.7.3 -> 1.8.1 (*) | | | +--- androidx.lifecycle:lifecycle-common:2.8.2 (c) | | | +--- androidx.lifecycle:lifecycle-livedata-core:2.8.2 (c) | | | +--- androidx.lifecycle:lifecycle-livedata-core-ktx:2.8.2 (c) | | | +--- androidx.lifecycle:lifecycle-runtime:2.8.2 (c) | | | +--- androidx.lifecycle:lifecycle-viewmodel:2.8.2 (c) | | | +--- androidx.lifecycle:lifecycle-viewmodel-ktx:2.8.2 (c) 27

Choose your dependencies wisely ▸ Prefer libraries using the same dependencies as your app: ▹ Same JSON parser (Kotlinx serialization, Moshi) ▹ Same image loader (Coil, Glide) ▹ Same network stack (Retrofit/OkHttp, Ktor). ▸ Avoid libraries with too many dependencies. 28

Choose your dependencies wisely ▸ Avoid heavy libraries (check size using APK Analyzer) ▸ Avoid libraries depending on kotlin-reflect (+ 1 MB dex!) (example: replace moshi-kotlin with moshi-kotlin-codegen) ▸ Replace RxJava with Kotlin coroutines. 29

Optimize Proguard rules Beyond the defaults 4

Optimize Proguard rules android { buildTypes { release { isMinifyEnabled = true proguardFiles( getDefaultProguardFile("proguard-android.txt"), "proguard-rules.pro" ) isShrinkResources = true } } } 31 build.gradle.kts -dontoptimize

Optimize Proguard rules android { buildTypes { release { isMinifyEnabled = true proguardFiles( getDefaultProguardFile("proguard-android.txt"), getDefaultProguardFile("proguard-android-optimize.txt"), "proguard-rules.pro" ) isShrinkResources = true } } } 32 build.gradle.kts

proguard-android-optimize.txt # Preserve some attributes that may be required for reflection. -keepattributes AnnotationDefault, EnclosingMethod, InnerClasses, RuntimeVisibleAnnotations, RuntimeVisibleParameterAnnotations, RuntimeVisibleTypeAnnotations, Signature 33

proguard-android-optimize.txt # Preserve some attributes that may be required for reflection. -keepattributes AnnotationDefault, EnclosingMethod, InnerClasses, RuntimeVisibleAnnotations, RuntimeVisibleParameterAnnotations, RuntimeVisibleTypeAnnotations, Signature # Preserve some attributes that may be required for reflection. -keepattributes RuntimeVisible*Annotations, AnnotationDefault 34

proguard-android-optimize.txt # Keep setters in Views so that animations can still work. -keepclassmembers public class * extends android.view.View { void set*(***); *** get*(); } 35 ObjectAnimator.ofInt(myView, "counter", 1, 4)

proguard-android-optimize.txt # Keep setters in Views so that animations can still work. -keepclassmembers public class * extends android.view.View { void set*(***); *** get*(); } 36 ObjectAnimator.ofInt(myView, "counter", 1, 4) ObjectAnimator.ofInt(myView, MyView.COUNTER, 1, 4)

proguard-android-optimize.txt # We want to keep methods in Activity that could be used in the XML attribute onClick. -keepclassmembers class * extends android.app.Activity { public void *(android.view.View); } 37

proguard-android-optimize.txt # For enumeration classes -keepclassmembers enum * { public static **[] values(); public static ** valueOf(java.lang.String); } 38 bundle.putSerializable("type", AnimalType.CAT)

proguard-android-optimize.txt # For enumeration classes -keepclassmembers enum * { public static **[] values(); public static ** valueOf(java.lang.String); } 39 bundle.putSerializable("type", AnimalType.CAT) bundle.putString("type", AnimalType.CAT.name) val type = enumValueOf(bundle.getString("type")!!)

-allowaccessmodification # Preserve some attributes that may be required for reflection. -keepattributes RuntimeVisible*Annotations, AnnotationDefault # For native methods -keepclasseswithmembernames class * { native ; } -keepclassmembers class * implements android.os.Parcelable { public static final ** CREATOR; } # Preserve annotated Javascript interface methods. -keepclassmembers class * { @android.webkit.JavascriptInterface ; } # The support libraries contains references to newer platform versions. # Don't warn about those in case this app is linking against an older # platform version. We know about them, and they are safe. -dontnote androidx.** -dontwarn androidx.** # This class is deprecated, but remains for backward compatibility. -dontwarn android.util.FloatMath # These classes are duplicated between android.jar and core-lambda-stubs.jar. -dontnote java.lang.invoke.** 40 Modern defaults

41 Impact of optimizing default Proguard rules

42 Impact of optimizing default Proguard rules

https://jakewharton.com/blog/ 43 More about R8 optimizations

Kotlin assertions import java.time.Instant class Demo { fun hello(name: String) { val now = Instant.now().toString() println("Hello $name at $now") } } 44 public final class Demo { public final void hello(@NotNull String name) { Intrinsics.checkNotNullParameter(name, "name"); String now = Instant.now().toString(); Intrinsics.checkNotNullExpressionValue(now, "Instant.now().toString()"); String var3 = "Hello " + name + " at " + now; System.out.println(var3); } } compiled into

android { buildTypes { release { kotlinOptions { freeCompilerArgs += listOf( "-Xno-param-assertions", "-Xno-call-assertions", "-Xno-receiver-assertions" ) } } } } 45 build.gradle.kts Remove some Kotlin assertions

# Remove Kotlin assertions -assumenosideeffects class kotlin.jvm.internal.Intrinsics { public static void checkNotNull(...); public static void checkExpressionValueIsNotNull(...); public static void checkNotNullExpressionValue(...); public static void checkParameterIsNotNull(...); public static void checkNotNullParameter(...); public static void checkReturnedValueIsNotNull(...); public static void checkFieldIsNotNull(...); public static void throwUninitializedPropertyAccessException(...); public static void throwNpe(...); public static void throwJavaNpe(...); public static void throwAssert(...); public static void throwIllegalArgument(...); public static void throwIllegalState(...); } 46 proguard-rules.pro Remove all Kotlin assertions

47 Impact of removing all Kotlin assertions

Debug your Proguard rules -dontobfuscate ▹ To be able to check which packages and classes are kept in dex files using the APK Analyzer. -printconfiguration proguard-config.txt ▹ Check the rules added by third-party libraries. 48 proguard-rules.pro

Examples of bad third-party library rules -keep class com.mylibrary.** { *; } -keep class * extends android.view.View { *; } -dontobfuscate -dontoptimize 49

Fixing bad third-party library rules ▸ Proguard rules are global to the app. ▸ A Proguard rule can not be overridden by another Proguard rule. ▸ Since AGP 7.3 (Sept 2022), Proguard rules can be excluded for a specific library, then can be copied and fixed in the app rules file. 50

Excluding Proguard rules of a specific library android { buildTypes { release { optimization.keepRules { ignoreFrom("com.badlibrary:badlibrary") } } } } 51 build.gradle.kts

fun patchDesugarConfig(config: Property) { val defaultConfig = config as org.gradle.api.internal.provider.DefaultProperty val patchedDesugarConfig = defaultConfig.provider.map { it.replace( "\"support_all_callbacks_from_library\":true", "\"support_all_callbacks_from_library\":false" ) } config.set(patchedDesugarConfig) } afterEvaluate { tasks.withType(com.android.build.gradle.internal.tasks.R8Task::class).configureEach { patchDesugarConfig(coreLibDesugarConfig) } tasks.withType(com.android.build.gradle.internal.tasks.L8DexDesugarLibTask::class).configureEach { patchDesugarConfig(libConfiguration) } } 52 build.gradle.kts Packaging Patching desugaring configuration

53 Impact of desugaring optimization

54

XML resources vs. shrinking Jetpack libraries using XML to load code 5

The shrinking process 56 STEP 3: Resources shrinking The resources shrinker removes all resources (including layouts) not referenced in the remaining code STEP 2: Code shrinking R8 removes unused code using the concatenated Proguard rules of: app + libraries + step 1 STEP 1: Scan + Configuration Proguard rules are added to keep: - Entry points in AndroidManifest.xml - Custom Views from all XML layouts

Shrinking process limitations 57 My App Material Components library Code Resources MainActivity.class (entry point) main_activity.xml CustomButton.class MaterialTimePicker.class TimePickerView.class material_timepicker_dialog.xml

Shrinking process limitations 58 My App Material Components library Code Resources MainActivity.class (entry point) main_activity.xml CustomButton.class MaterialTimePicker.class TimePickerView.class material_timepicker_dialog.xml Step 1 + MainActivity.class + CustomButton.class + TimePickerView.class

Shrinking process limitations 59 My App Material Components library Code Resources MainActivity.class (entry point) main_activity.xml CustomButton.class TimePickerView.class material_timepicker_dialog.xml Step 2

Shrinking process limitations 60 My App Material Components library Code Resources MainActivity.class (entry point) main_activity.xml CustomButton.class TimePickerView.class Step 3 Unreachable code

android { sourceSets { getByName("main") { res.srcDir("src/main/res-override") } } } 61 A workaround build.gradle.kts

Library resources overriding: Example case study 62

Down the Rabbit hole. 63

▸ The AppCompat and Material Components libraries use a custom layout inflater to replace 14 system widgets: Button, TextView, CheckBox, ImageView, … ▸ These widgets and their resources are always included. 64 Shrinking limitations of XML-based Jetpack libraries com.google.android.material .button.MaterialButton inflate

▸ The CoordinatorLayout library adds a Proguard rule to keep every CoordinatorLayout.Behavior. They are created via reflection: 65 Shrinking limitations of XML-based Jetpack libraries

▸ The RecyclerView library adds a Proguard rule to keep all LayoutManagers. They may be created via reflection: 66 Shrinking limitations of XML-based Jetpack libraries

▸ The Preferences library adds a Proguard rule to keep all 11 preference types. They are created via reflection. ▸ The Transitions library includes the code of all 10 transition types when TransitionInflater is used. ▸ … 67 Shrinking limitations of XML-based Jetpack libraries

68

“ How do we move on from the code + XML duo? 69

Jetpack Compose 70

Compose Everywhere Going 100% Compose 6

▸ XML resources are replaced with Kotlin DSL. ▸ No reflection or Proguard rules needed. But: ▸ The app needs to include the Compose runtime (~900 KB dex code). 72 Compose shrinks best

▸ Compose-only apps don’t need AppCompat. ▸ Check your library dependencies! ▹ ./gradlew app:dependencies > deps.txt +--- io.insert-koin:koin-androidx-compose:3.5.6 | +--- io.insert-koin:koin-android:3.5.6 | | +--- io.insert-koin:koin-core:3.5.6 | | +--- androidx.appcompat:appcompat:1.6.1 73 Compose UI does not depend on AppCompat (or Material Components)

(after shrinking) + AppCompat 1.7.0 + AppCompat 1.7.0 + Material Components 1.12.0 /res + 195 KB + 288 KB *.dex + 426 KB + 929 KB Apk file (3 locales) + 479 KB + 1006 KB 74 Overhead of AppCompat & Material Components

▸ Double-check that the library doesn’t require it. dependencies { implementation(libs.koin.androidx.compose) { exclude(group = "androidx.appcompat", module = "appcompat") } } // Alternatively configurations.configureEach { exclude(group = "androidx.appcompat", module = "appcompat") } 75 build.gradle.kts Quick Fix: Exclude AppCompat

76 Better Fix: Send a pull request

77 Case study: Migrating an entire app to Compose T.B.D. 😅

78 A Compose migration example: Tivi https:/ /github.com/chrisbanes/tivi

79 THANKS! Any questions? Find me at: ▸ bladecoder@androiddev.social ▸ bladecoder.medium.com ▸ github.com/cbeyls Credits ▸ Presentation template by SlidesCarnival ▸ Illustrations from Pixabay ▸ Some images by Sergei Tikhonov ▸ Movie shot from “The Matrix”.