Android ClassNotFoundException in Activities: How Can I Fix This Runtime Error?

ClassNotFoundException Error in Android Activities: Resolving the Problem

This error, commonly encountered when trying to start an Android Activity, indicates that the Activity's class cannot be instantiated. The error message typically includes a stack trace like the one provided in the question.

One of the reasons for this issue is an incorrect AndroidManifest.xml file. However, since the manifest file appears to be configured correctly in the given example, there could be other underlying causes.

One potential solution involves verifying that the library project is properly referenced from the main project. Two incorrect methods are described:

1. Wrong Method: Adding the library project as a dependency project to the main project via Java Build Path -> Projects -> Add.... This can lead to compilation success without errors but result in the ClassNotFoundException at runtime.
2. Correct Method: Referencing the library project properly using Build -> Order and Export -> Android -> Library projects. This ensures that all required resources are included.

Another likely cause is an upgrade in the SDK tools. A suggested solution involves using a modified version of ProGuard, i.e. ProGuard with Android optimization options, and/or re-exporting the project as an Android library to resolve potential conflicts during packaging.

The solution provided by the original poster mentions a possible solution related to referencing the library project in the Library section of the main project's Android settings. By specifying the library project as a dependent project in this way, the necessary resources are correctly included, resolving the issue.

To recap, resolving the ClassNotFoundException error can involve verifying the following:

• Correct manifest file configuration
• Proper referencing of the library project in the main project's Android settings
• Compatibility of SDK tools and ProGuard settings
• Exclusion of conflicting or outdated library dependencies

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