Resolving Android Activity ClassNotFoundException After Refactoring

What causes the ClassNotFoundException in Android after refactoring an app into a framework library?

06-02 18:22:35.529: E/AndroidRuntime(586): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.matthewrathbone.eastersays/com.matthewrathbone.eastersays.EasterSimonSaysActivity}: java.lang.ClassNotFoundException: com.matthewrathbone.eastersays.EasterSimonSaysActivity

The ClassNotFoundException in your Android application occurs when the system cannot find the specified Activity class, which often happens after refactoring code into a library. Here’s how you can diagnose and fix the issue.

<activity
    android:name=".EasterSimonSaysActivity"
    android:label="@string/app_name">
    <intent-filter>
        <action android:name="android.intent.action.MAIN" />
        <category android:name="android.intent.category.LAUNCHER" />
    </intent-filter>
</activity>

Causes

• The class name in the manifest file is incorrect.
• The refactoring introduced package name mismatches in the project.
• Build or sync issues might prevent the application from recognizing the refactored class.

Solutions

• Ensure the package name in your manifest matches the package declaration in your class files.
• Recheck the build configuration to confirm all dependencies are properly linked.
• Clean and rebuild the project to ensure all components are correctly generated.

Mistake: The Activity is not declared correctly in the AndroidManifest.xml file.

Solution: Verify that the android:name attribute in the manifest correctly references the Activity class.

Mistake: The class was moved but retains an old package declaration.

Solution: Ensure the package declaration at the top of your Java file matches its actual location in the project structure.

Mistake: The project was not properly cleaned or rebuilt after refactoring.

Solution: Perform a clean build of your project by going to Build > Clean Project and then Build > Rebuild Project.