Android Gradle Build Error: Could not create an instance of LibraryVariantBuilderImpl

Problem Statement

When building an Android application (commonly in Flutter projects), you may encounter the error:

FAILURE: Build failed with an exception.

* What went wrong:
A problem occurred configuring project ':wakelock'.
> Could not create an instance of type com.android.build.api.variant.impl.LibraryVariantBuilderImpl.
   > Namespace not specified. Please specify a namespace in the module's build.gradle file

This error occurs even if your main app/build.gradle already defines a namespace. The root cause is typically:

• Using Android Gradle Plugin (AGP) 8+ which requires explicit namespaces
• Third-party library modules (like wakelock in the example) that lack namespace definitions
• Build configuration conflicts after updating development environments or dependencies

Solutions

1. Configure Namespace for All Subprojects (Recommended)

TIP

This solution forces namespace resolution for all library dependencies

Add this code to your project-level build.gradle (android/build.gradle):

allprojects {
    repositories {
        google()
        mavenCentral()
    }
}

subprojects {
    afterEvaluate { project ->
        if (project.hasProperty('android')) {
            project.android {
                if (namespace == null) {
                    namespace project.group
                }
            }
        }
    }
}

For Kotlin DSL (build.gradle.kts):

allprojects {
    repositories {
        google()
        mavenCentral()
    }
}

subprojects {
    afterEvaluate {
        if (plugins.hasPlugin("com.android.library")) {
            extensions.configure<com.android.build.gradle.LibraryExtension>("android") {
                if (namespace == null) {
                    namespace = group.toString()
                }
            }
        }
    }
}

Key Notes

• Place this BEFORE any other subprojects blocks
• Applies only to library modules (com.android.library)
• Does not override existing namespaces

Perform a clean build after applying:

flutter clean
flutter run

2. Fix AndroidManifest.xml in Problematic Modules

If you encounter subsequent manifest errors like:

Execution failed for task ':app:processDebugManifest'

Add tools namespace to empty manifests in libraries:

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools">
    <!-- Content -->
</manifest>

3. Update Outdated Dependencies

Replace incompatible packages with updated alternatives. For wakelock:

# pubspec.yaml
dependencies:
  wakelock_plus: ^4.0.0 # Instead of wakelock

4. Downgrade AGP (Temporary Workaround)

Only use if other solutions fail:

1. Downgrade Gradle in gradle-wrapper.properties:

   distributionUrl=https\://services.gradle.org/distributions/gradle-7.6.3-all.zip

2. Downgrade AGP in project-level build.gradle:

   plugins {
       id "com.android.application" version "7.3.0" apply false
   }

Explanation

Why This Happens

• AGP 8+ requires all modules to declare namespace
• Some older libraries omit this declaration
• Build systems can't resolve dependencies when namespaces are missing

Solution Priority Table

Solution	Recommended For	Long-term Stability
Subproject Configuration	Projects with multiple dependencies	✅ Excellent
Dependency Updates	Projects using known outdated packages	✅ Best
Manifest Fixes	Secondary manifest-related errors	⚠️ Case-specific
AGP Downgrade	Temporary emergencies	❌ Not recommended

Additional Best Practices

1. Verify AGP versions in all build.gradle files
2. Ensure consistency in these files:
   • android/build.gradle
   • android/app/build.gradle
   • android/settings.gradle
3. Always run flutter clean after Gradle modifications
4. Verify namespace syntax in libraries:

   android {
       namespace 'com.example.library' // Must be present
   }

Common Pitfalls

• Applying configurations to wrong build.gradle file (app/ vs project-level)
• Forgetting to sync Gradle after changes
• Not fully cleaning build artifacts before retrying