If your app has a minSdk
of API 20 or lower and your app and the
libraries it references exceed 65,536 methods, you encounter the following build error that
indicates your app has reached the limit of the Android build architecture:
trouble writing output: Too many field references: 131000; max is 65536. You may try using --multi-dex option.
Older versions of the build system report a different error, which is an indication of the same problem:
Conversion to Dalvik format failed: Unable to execute dex: method ID not in [0, 0xffff]: 65536
These error conditions display a common number: 65536. This number represents the total number of references that can be invoked by the code within a single Dalvik Executable (DEX) bytecode file. This page explains how to move past this limitation by enabling an app configuration known as multidex, which allows your app to build and read multiple DEX files.
About the 64K reference limit
Android app (APK) files contain executable bytecode files in the form of Dalvik Executable (DEX) files, which contain the compiled code used to run your app. The Dalvik Executable specification limits the total number of methods that can be referenced within a single DEX file to 65,536—including Android framework methods, library methods, and methods in your own code.
In the context of computer science, the term kilo, or K, denotes 1024 (or 2^10). Because 65,536 is equal to 64x1024, this limit is referred to as the _64K reference limit_.Multidex support prior to Android 5.0
Versions of the platform prior to Android 5.0 (API level 21) use the Dalvik
runtime for executing app code. By default, Dalvik limits apps to a single
classes.dex
bytecode file per APK. To get around this
limitation, add the multidex library to the module-level build.gradle
or
build.gradle.kts
file:
Groovy
dependencies { def multidex_version = "2.0.1" implementation "androidx.multidex:multidex:$multidex_version" }
Kotlin
dependencies { val multidex_version = "2.0.1" implementation("androidx.multidex:multidex:$multidex_version") }
This library becomes part of the primary DEX file of your app and then manages access to the additional DEX files and the code they contain. To view the current versions for this library, see multidex versions.
For more details, see the section about how to configure your app for multidex.Multidex support for Android 5.0 and higher
Android 5.0 (API level 21) and higher uses a runtime called ART that
natively supports loading multiple DEX files from APK files. ART
performs pre-compilation at app install time, scanning for
classesN.dex
files and compiling them into a single
OAT file for
execution by the Android device. Therefore, if your minSdkVersion
is 21 or higher, multidex is enabled by default and you don't need the multidex library.
For more information on the Android 5.0 runtime, read Android Runtime (ART) and Dalvik.
Note: When running your app using Android Studio, the build is optimized for the target devices you deploy to. This includes enabling multidex when the target devices are running Android 5.0 and higher. Since this optimization is applied only when deploying your app using Android Studio, you might still need to configure your release build for multidex to avoid the 64K limit.
Avoid the 64K limit
Before configuring your app to enable use of 64K or more method references, take steps to reduce the total number of references called by your app code, including methods defined by your app code or included libraries.
The following strategies can help you avoid hitting the DEX reference limit:
- Review your app's direct and transitive dependencies
- Consider whether the value of any large library dependency you include in your app outweighs the amount of code being added to the app. A common but problematic pattern is to include a very large library because a few utility methods were useful. Reducing your app code dependencies can often help you avoid the DEX reference limit.
- Remove unused code with R8
- Enable code shrinking to run R8 for your release builds. Enable shrinking to help ensure that you aren't shipping unused code with your APKs. If code shrinking is configured correctly, it can also remove unused code and resources from your dependencies.
Using these techniques can help you decrease the overall size of your APK and avoid the need for multidex in your app.
Configure your app for multidex
Note: If yourminSdkVersion
is set to 21 or higher, multidex is enabled by default
and you don't need the multidex library.
If your minSdkVersion
is set to 20 or lower, then you
must use the
multidex library and make
the following modifications to your app project:
-
Modify the module-level
build.gradle
file to enable multidex and add the multidex library as a dependency, as shown here:Groovy
android { defaultConfig { ... minSdkVersion 15 targetSdkVersion 33 multiDexEnabled true } ... } dependencies { implementation "androidx.multidex:multidex:2.0.1" }
Kotlin
android { defaultConfig { ... minSdk = 15 targetSdk = 33 multiDexEnabled = true } ... } dependencies { implementation("androidx.multidex:multidex:2.0.1") }
- Depending on whether you override the
Application
class, perform one of the following:If you don't override the
Application
class, edit your manifest file to setandroid:name
in the<application>
tag as follows:<?xml version="1.0" encoding="utf-8"?> <manifest xmlns:android="http://schemas.android.com/apk/res/android" package="com.example.myapp"> <application android:name="androidx.multidex.MultiDexApplication" > ... </application> </manifest>
If you do override the
Application
class, change it to extendMultiDexApplication
, as follows:Kotlin
class MyApplication : MultiDexApplication() {...}
Java
public class MyApplication extends MultiDexApplication { ... }
If you override the
Application
class but it's not possible to change the base class, then instead override theattachBaseContext()
method and callMultiDex.install(this)
to enable multidex:Kotlin
class MyApplication : SomeOtherApplication() { override fun attachBaseContext(base: Context) { super.attachBaseContext(base) MultiDex.install(this) } }
Java
public class MyApplication extends SomeOtherApplication { @Override protected void attachBaseContext(Context base) { super.attachBaseContext(base); MultiDex.install(this); } }
Caution: Don't execute
MultiDex.install()
or any other code through reflection or JNI beforeMultiDex.install()
is complete. Multidex tracing will not follow those calls, causingClassNotFoundException
or verify errors due to a bad class partition between DEX files.
Now when you build your app, the Android build tools construct a primary DEX
file (classes.dex
) and supporting DEX files
(classes2.dex
, classes3.dex
, and so on) as needed.
The build system then packages all DEX files into your APK.
At runtime, instead of searching only in the main
classes.dex
file, the multidex APIs use a special class loader to search all of the
available DEX files for your methods.
Limitations of the multidex library
The multidex library has some known limitations. When you incorporate the library into your app build configuration, consider the following:
- The installation of DEX files during startup onto a device's data partition is complex and can result in Application Not Responding (ANR) errors if the secondary DEX files are large. To avoid this issue, enable code shrinking to minimize the size of DEX files and remove unused portions of code.
- When running on versions prior to Android 5.0 (API level 21), using
multidex is not enough to work around the linearalloc limit (issue 37008143). This limit was increased in
Android 4.0 (API level 14), but that didn't solve the issue completely.
On versions lower than Android 4.0, you might reach the linearalloc limit before reaching the DEX index limit. So if you are targeting API levels lower than 14, test thoroughly on those versions of the platform, because your app might have issues at startup or when particular groups of classes are loaded.
Code shrinking can reduce or possibly eliminate these issues.
Declare classes required in the primary DEX file
When building each DEX file for a multidex app, the build tools perform
complex decision-making to determine which classes are needed in the primary DEX
file so that your app can start successfully. If any class that's required
during startup is not provided in the primary DEX file, then your app crashes
with the error java.lang.NoClassDefFoundError
.
The build tools recognize the code paths for code that's accessed directly from your app code. However, this problem can occur when the code paths are less visible, such as when a library you use has complex dependencies. For example, if the code uses introspection or invocation of Java methods from native code, then those classes might not be recognized as required in the primary DEX file.
If you receive java.lang.NoClassDefFoundError
, you
must manually specify the additional classes required in the primary DEX
file by declaring them with the multiDexKeepProguard
property in your build type. If a class is matched in
the multiDexKeepProguard
file, then that class
is added to the primary DEX file.
multiDexKeepProguard property
The multiDexKeepProguard
file uses the same format as ProGuard and supports the
entire ProGuard grammar. For more information about how to customize what is kept in your app, see
Customize which code to keep.
The file you specify in multiDexKeepProguard
should contain -keep
options in any valid ProGuard syntax. For example,
-keep com.example.MyClass.class
. You can create a file called
multidex-config.pro
that looks like this:
-keep class com.example.MyClass -keep class com.example.MyClassToo
If you want to specify all classes in a package, the file looks like this:
-keep class com.example.** { *; } // All classes in the com.example package
Then you can declare that file for a build type, as follows:
Groovy
android { buildTypes { release { multiDexKeepProguard file('multidex-config.pro') ... } } }
Kotlin
android { buildTypes { getByName("release") { multiDexKeepProguard = file("multidex-config.pro") ... } } }
Optimize multidex in development builds
A multidex configuration requires significantly increased build processing time because the build system must make complex decisions about which classes must be included in the primary DEX file and which classes can be included in secondary DEX files. This means that incremental builds using multidex typically take longer and can potentially slow your development process.
To mitigate longer incremental build times, use
pre-dexing to reuse multidex output between builds.
Pre-dexing relies on an ART format available only on Android 5.0
(API level 21) and higher. If you're using Android Studio, the IDE automatically uses pre-dexing
when deploying your app to a device running Android 5.0 (API level 21) or higher.
However, if you're running Gradle builds from the command line, you need to set the
minSdkVersion
to 21 or higher to enable pre-dexing.
minSdkVersion
,
as shown:
Groovy
android { defaultConfig { ... multiDexEnabled true // The default minimum API level you want to support. minSdkVersion 15 } productFlavors { // Includes settings you want to keep only while developing your app. dev { // Enables pre-dexing for command-line builds. When using // Android Studio 2.3 or higher, the IDE enables pre-dexing // when deploying your app to a device running Android 5.0 // (API level 21) or higher, regardless of minSdkVersion. minSdkVersion 21 } prod { // If you've configured the defaultConfig block for the production version of // your app, you can leave this block empty and Gradle uses configurations in // the defaultConfig block instead. You still need to include this flavor. // Otherwise, all variants use the "dev" flavor configurations. } } buildTypes { release { minifyEnabled true proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro' } } } dependencies { implementation "androidx.multidex:multidex:2.0.1" }
Kotlin
android { defaultConfig { ... multiDexEnabled = true // The default minimum API level you want to support. minSdk = 15 } productFlavors { // Includes settings you want to keep only while developing your app. create("dev") { // Enables pre-dexing for command-line builds. When using // Android Studio 2.3 or higher, the IDE enables pre-dexing // when deploying your app to a device running Android 5.0 // (API level 21) or higher, regardless of minSdkVersion. minSdk = 21 } create("prod") { // If you've configured the defaultConfig block for the production version of // your app, you can leave this block empty and Gradle uses configurations in // the defaultConfig block instead. You still need to include this flavor. // Otherwise, all variants use the "dev" flavor configurations. } } buildTypes { getByName("release") { isMinifyEnabled = true proguardFiles(getDefaultProguardFile("proguard-android.txt"), "proguard-rules.pro") } } } dependencies { implementation("androidx.multidex:multidex:2.0.1") }
To learn more strategies to help improve build speeds from either Android Studio or the command line, read Optimize your build speed. For more information about using build variants, see Configure build variants.
Tip: If you have different build variants for different
multidex needs, you can provide a different manifest file for each
variant so only the file for API level 20 and lower changes the
<application>
tag name. You can also
create a different Application
subclass for each variant so
only the subclass for API level 20 and lower extends the MultiDexApplication
class or
calls MultiDex.install(this)
.
Test multidex apps
When you write instrumentation tests for multidex apps, no additional configuration is required
if you use a
MonitoringInstrumentation
or an
AndroidJUnitRunner
instrumentation. If you use another
Instrumentation
,
then you must override its onCreate()
method with the following code:
Kotlin
fun onCreate(arguments: Bundle) { MultiDex.install(targetContext) super.onCreate(arguments) ... }
Java
public void onCreate(Bundle arguments) { MultiDex.install(getTargetContext()); super.onCreate(arguments); ... }