Advanced App Shrinking Techniques

With the inner complexity of Android apps gradually increasing over the years, it has become crucial to use tools to reduce their footprint in production. But simply enabling code and resource shrinking is not enough to make your release builds as small as they could be!

In this talk, we're going to take a full tour of the available techniques to put apps on a diet, including undocumented ones. We will see how Jetpack Compose enables new minification opportunities compared to the classic Views system. We will discover the limitations of R8 and the resources shrinker and figure out how to work around them in order to eliminate the last unused bytes of APK files.

This will be illustrated with concrete file sizes and case studies of real applications.

Learn how to tweak your code, resources and configuration to make your apps lighter than ever!

Transcript

1. ADVANCED ANDROID APP SHRINKING TECHNIQUES In Search of Lightness: Christophe Beyls bladecoder@androiddev.social
2. 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. 3 Medium-sized app Large app FOSDEM Companion https://github.com/cbeyls/fosdem-companion-android Tusky https://github.com/tuskyapp/Tusky
4. 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
5. 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. 6 Android Studio APK Analyzer Browse and explore all file types.
7. The basics android { buildTypes { release { isMinifyEnabled = true proguardFiles( getDefaultProguardFile("proguard-android.txt"), "proguard-rules.pro" ) isShrinkResources = true } } } 7 build.gradle.kts
8. The basics android { buildTypes { release { isMinifyEnabled = true proguardFiles( getDefaultProguardFile("proguard-android.txt"), "proguard-rules.pro" ) isShrinkResources = true } } } 8 Remove unused code build.gradle.kts
9. The basics android { buildTypes { release { isMinifyEnabled = true proguardFiles( getDefaultProguardFile("proguard-android.txt"), "proguard-rules.pro" ) isShrinkResources = true } } } 9 Remove unused resources build.gradle.kts
10. 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
11. Optimize images Not all pixels are created equal 1
12. (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. 13 640x640 transparent PNG 400,4 Kb 640x640 transparent WebP 106,1 Kb Original Lossy WebP (drawing mode, q98)
14. 14 640x640 transparent PNG 400,4 Kb 640x640 transparent WebP 106,1 Kb Original Lossy WebP (drawing mode, q98)
15. ▸ 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
16. https://github.com/alexjlockwood/avocado 16 Avocado: optimize vector drawables
17. Optimize resources Remove, remove, remove 2
18. 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
19. Remove unsupported locales: Example case study 19
20. 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
21. APK meta data 21
22. 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
23. 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
24. 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
25. APK split per CPU architecture android { splits { abi { isEnable = true reset() include ("x86", "armeabi-v7a", "arm64-v8a") isUniversalApk = false } } } 25 build.gradle.kts
26. Optimize dependencies Select and deduplicate 3
27. 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
28. 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
29. 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
30. Optimize Proguard rules Beyond the defaults 4
31. Optimize Proguard rules android { buildTypes { release { isMinifyEnabled = true proguardFiles( getDefaultProguardFile("proguard-android.txt"), "proguard-rules.pro" ) isShrinkResources = true } } } 31 build.gradle.kts -dontoptimize
32. 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
33. proguard-android-optimize.txt # Preserve some attributes that may be required for reflection. -keepattributes AnnotationDefault, EnclosingMethod, InnerClasses, RuntimeVisibleAnnotations, RuntimeVisibleParameterAnnotations, RuntimeVisibleTypeAnnotations, Signature 33
34. 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
35. 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)
36. 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)
37. 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 <Button android:id="@+id/button" android:onClick="onButtonClick" android:text="@string/about_text" />
38. proguard-android-optimize.txt # For enumeration classes -keepclassmembers enum * { public static **[] values(); public static ** valueOf(java.lang.String); } 38 bundle.putSerializable("type", AnimalType.CAT)
39. 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<AnimalType>(bundle.getString("type")!!)
40. -allowaccessmodification # Preserve some attributes that may be required for reflection. -keepattributes RuntimeVisible*Annotations, AnnotationDefault # For native methods -keepclasseswithmembernames class * { native <methods>; } -keepclassmembers class * implements android.os.Parcelable { public static final ** CREATOR; } # Preserve annotated Javascript interface methods. -keepclassmembers class * { @android.webkit.JavascriptInterface <methods>; } # 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. 41 Impact of optimizing default Proguard rules
42. 42 Impact of optimizing default Proguard rules
43. https://jakewharton.com/blog/ 43 More about R8 optimizations
44. 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
45. android { buildTypes { release { kotlinOptions { freeCompilerArgs += listOf( "-Xno-param-assertions", "-Xno-call-assertions", "-Xno-receiver-assertions" ) } } } } 45 build.gradle.kts Remove some Kotlin assertions
46. # 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. 47 Impact of removing all Kotlin assertions
48. 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
49. Examples of bad third-party library rules -keep class com.mylibrary.** { *; } -keep class * extends android.view.View { *; } -dontobfuscate -dontoptimize 49
50. 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
51. Excluding Proguard rules of a specific library android { buildTypes { release { optimization.keepRules { ignoreFrom("com.badlibrary:badlibrary") } } } } 51 build.gradle.kts
52. fun patchDesugarConfig(config: Property<String>) { val defaultConfig = config as org.gradle.api.internal.provider.DefaultProperty<String> 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. 53 Impact of desugaring optimization
55. XML resources vs. shrinking Jetpack libraries using XML to load code 5
56. 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
57. 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
58. 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
59. 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
60. 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
61. android { sourceSets { getByName("main") { res.srcDir("src/main/res-override") } } } 61 A workaround build.gradle.kts <merge />
62. Library resources overriding: Example case study 62
63. Down the Rabbit hole. 63
64. ▸ The AppCompat and Material Components libraries use a custom layout inflater to replace 14 system widgets: Button, TextView, CheckBox, ImageView, … <Button android:text="@string/button_text" android:layout_width="match_parent" android:layout_height="wrap_content" /> ▸ These widgets and their resources are always included. 64 Shrinking limitations of XML-based Jetpack libraries com.google.android.material .button.MaterialButton inflate
65. ▸ The CoordinatorLayout library adds a Proguard rule to keep every CoordinatorLayout.Behavior. They are created via reflection: <androidx.coordinatorlayout.widget.CoordinatorLayout> <com.google.android.material.appbar.AppBarLayout /> <androidx.core.widget.NestedScrollView app:layout_behavior="@string/appbar_scrolling_view_behavior" /> </androidx.coordinatorlayout.widget.CoordinatorLayout> 65 Shrinking limitations of XML-based Jetpack libraries
66. ▸ The RecyclerView library adds a Proguard rule to keep all LayoutManagers. They may be created via reflection: <androidx.recyclerview.widget.RecyclerView android:id="@android:id/list" android:layout_width="match_parent" android:layout_height="match_parent" app:layoutManager="androidx.recyclerview.widget.LinearLayoutManager" /> 66 Shrinking limitations of XML-based Jetpack libraries
67. ▸ 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
69. “ How do we move on from the code + XML duo? 69
70. Jetpack Compose 70
71. Compose Everywhere Going 100% Compose 6
72. ▸ 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
73. ▸ 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)
74. (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
75. ▸ 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. 76 Better Fix: Send a pull request
77. 77 Case study: Migrating an entire app to Compose T.B.D. 😅
78. 78 A Compose migration example: Tivi https:/ /github.com/chrisbanes/tivi
79. 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”.