If your app has a[`minSdk`of API 20 or lower](https://developer.android.com/build/multidex#mdex-pre-l)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)](https://source.android.com/devices/tech/dalvik/dex-format)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*](https://en.wikipedia.org/wiki/Kilo-), 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

```groovy
dependencies {
    def multidex_version = "2.0.1"
    implementation "androidx.multidex:multidex:$multidex_version"
}
```

### Kotlin

```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](https://developer.android.com/jetpack/androidx/releases/multidex#2.0.1).
For more details, see the section about how to[configure your app for multidex](https://developer.android.com/build/multidex#mdex-gradle).

### 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`classes`<var translate="no">N</var>`.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](https://source.android.com/devices/tech/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](https://developer.android.com/build/multidex#mdex-gradle)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](https://developer.android.com/studio/build/shrink-code)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 your`minSdkVersion`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](https://developer.android.com/jetpack/androidx/releases/multidex)and make the following modifications to your app project:

1. Modify the module-level`build.gradle`file to enable multidex and add the multidex library as a dependency, as shown here:

   ### Groovy

   ```groovy
   android {
       defaultConfig {
           ...
           minSdkVersion 15 
           targetSdkVersion 36
           multiDexEnabled true
       }
       ...
   }

   dependencies {
       implementation "androidx.multidex:multidex:2.0.1"
   }
   ```

   ### Kotlin

   ```kotlin
   android {
       defaultConfig {
           ...
           minSdk = 15 
           targetSdk = 36
           multiDexEnabled = true
       }
       ...
   }

   dependencies {
       implementation("androidx.multidex:multidex:2.0.1")
   }
   ```
2. Depending on whether you override the[`Application`](https://developer.android.com/reference/android/app/Application)class, perform one of the following:
   - If you don't override the`Application`class, edit your manifest file to set`android:name`in the`<application>`tag as follows:

     ```xml
     <?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 extend`MultiDexApplication`, as follows:

     ### Kotlin

     ```kotlin
     class MyApplication : MultiDexApplication() {...}
     ```

     ### Java

     ```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 the[`attachBaseContext()`](https://developer.android.com/reference/android/content/ContextWrapper#attachBaseContext(android.content.Context))method and call`MultiDex.install(this)`to enable multidex:

     ### Kotlin

     ```kotlin
     class MyApplication : SomeOtherApplication() {

         override fun attachBaseContext(base: Context) {
             super.attachBaseContext(base)
             MultiDex.install(this)
         }
     }
     ```

     ### Java

     ```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 before`MultiDex.install()`is complete. Multidex tracing will not follow those calls, causing`ClassNotFoundException`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](https://developer.android.com/studio/build/shrink-code)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](https://issuetracker.google.com/issues/37008143)). This limit was increased in Android 4.0 (API level 14), but that didn't solve the issue completely.

  <br />

  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](https://developer.android.com/studio/build/shrink-code)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`](https://developer.android.com/reference/tools/gradle-api/8.13/com/android/build/api/dsl/VariantDimension#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](https://developer.android.com/studio/build/shrink-code#keep-code).

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

```groovy
android {
    buildTypes {
        release {
            multiDexKeepProguard file('multidex-config.pro')
            ...
        }
    }
}
```

### Kotlin

```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.
To preserve settings for your production build, you can create two versions of your app[using product flavors](https://developer.android.com/studio/build/build-variants#product-flavors)---one version with a development flavor and one version with a release flavor---with different values for`minSdkVersion`, as shown:

<br />

### Groovy

```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

```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](https://developer.android.com/studio/build/optimize-your-build). For more information about using build variants, see[Configure build variants](https://developer.android.com/studio/build/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`](https://developer.android.com/reference/androidx/test/runner/MonitoringInstrumentation)or an[`AndroidJUnitRunner`](https://developer.android.com/reference/androidx/test/runner/AndroidJUnitRunner)instrumentation. If you use another[`Instrumentation`](https://developer.android.com/reference/android/app/Instrumentation), then you must override its`onCreate()`method with the following code:  

### Kotlin

```kotlin
fun onCreate(arguments: Bundle) {
  MultiDex.install(targetContext)
  super.onCreate(arguments)
  ...
}
```

### Java

```java
public void onCreate(Bundle arguments) {
  MultiDex.install(getTargetContext());
  super.onCreate(arguments);
  ...
}
```
| **Notes:** Don't use`MultiDexTestRunner`, which is deprecated; use[`AndroidJUnitRunner`](https://developer.android.com/reference/androidx/test/runner/AndroidJUnitRunner)instead.