Unable to execute dex: Multiple dex files define Lbolts/AggregateException

Understanding the “Unable to execute dex: Multiple dex files define Lbolts/AggregateException” Error

This error occurs during the build process of an Android application and indicates that two or more library files (dex files) are attempting to define the same class, causing a conflict.

Causes of the Error

1. Conflicting Dependencies

• Multiple libraries in your project depend on the same library, but with different versions. For example, multiple libraries may require different versions of the Bolts framework.

2. Direct Inclusion of Duplicate Libraries

• You might have accidentally included the same library (such as Bolts) in your project multiple times.

3. ProGuard Issues

• In some cases, ProGuard’s minification process can obfuscate classes in a way that leads to conflicts.

Troubleshooting Steps

1. Analyze Dependencies

• Use your build system’s dependency management tools (e.g., Gradle in Android Studio) to review your project’s dependencies.
• Identify libraries that depend on the conflicting class (in this case, Lbolts/AggregateException).
• Check if any libraries have multiple versions included.

2. Resolve Dependency Conflicts

• **Choose a Single Version:** If multiple libraries rely on the same library, select a compatible version that works for all of them.
• **Exclude Conflicting Dependencies:** If you only need specific parts of a library, exclude the conflicting parts using the `exclude` keyword in your dependencies declaration.

3. Remove Duplicate Library Inclusion

• Carefully examine your project structure and remove any duplicate library inclusions. Ensure that the Bolts library is present only once in your project.

4. Adjust ProGuard Configuration

• If you suspect ProGuard is causing the issue, review your ProGuard rules file and ensure that it does not accidentally cause class name collisions.
• Try temporarily disabling ProGuard to see if the error disappears. If it does, investigate your ProGuard configuration further.

Example: Resolving a Dependency Conflict in Gradle

Code Snippet

dependencies {
    implementation("com.android.support:appcompat-v7:28.0.0") // Example conflicting dependency
    implementation("com.bolts:bolts-android:1.4.0") // Another conflicting dependency

    // Exclude the conflicting class from the 'appcompat-v7' dependency
    implementation("com.android.support:appcompat-v7:28.0.0") {
        exclude group: "com.bolts", module: "bolts-android" 
    }
}

Output

This example demonstrates how to exclude the conflicting Bolts library from the appcompat-v7 dependency using Gradle’s `exclude` directive. This ensures that the library is only included once from its direct dependency.