Gradle can't find protobuf generated class (Android DataStore)

2 min read 05-10-2024

Gradle can't find protobuf generated class (Android DataStore)

Gradle's Protobuf Puzzle: Solving the Missing Generated Class Problem in Android DataStore

Using Google's Protocol Buffers (protobuf) for data serialization is a popular choice for Android developers, especially when working with Android DataStore. However, you might encounter a frustrating issue: Gradle fails to find the generated protobuf classes, leading to build errors and a stalled development process.

Let's break down the problem and provide solutions to get your project back on track.

The Scenario: A Missing Protobuf Class

Imagine this: you've diligently defined your protobuf message, generated the Java classes using the protoc compiler, and configured your Gradle build file. Yet, when you attempt to use the generated class in your Android DataStore implementation, Gradle throws an error: "Cannot resolve symbol 'yourGeneratedClassName'".

Here's a snippet of the typical setup that might lead to this problem:

dependencies {
    implementation("com.google.protobuf:protobuf-java:3.21.5")
    implementation("androidx.datastore:datastore-preferences:1.0.0")
    implementation("androidx.datastore:datastore-core:1.0.0")
}

protobuf {
    protoc {
        artifact = "com.google.protobuf:protoc:3.21.5"
    }
    generateProtoTasks {
        all().each { task ->
            task.builtins {
                java {
                    option("lite")
                }
            }
        }
    }
}

The error message clearly points to a missing class. Why does this happen?

Understanding the Cause: Gradle's Classpath and Protobuf's Output

The root of the problem lies in how Gradle manages dependencies and where Protobuf generates its output.

Gradle's Classpath: Gradle defines a specific path where it looks for compiled classes. If the generated protobuf classes are not present in this path, Gradle cannot find them.
Protobuf's Output: By default, the protoc compiler generates output files in the build/generated/source/proto directory. However, this location might not be included in Gradle's classpath, leading to the missing class error.

Solutions to the Protobuf Puzzle:

Here's how you can resolve this issue:

Explicitly Include the Generated Source Directory:
- Modify your build.gradle file to include the generated protobuf source directory in the compilation classpath:
```
sourceSets {
    main {
        java {
            srcDir 'build/generated/source/proto/main/java' // Add this line
        }
    }
}
```
Use a Gradle Plugin:
- Utilize a plugin like the protobuf-gradle-plugin to simplify the process of generating protobuf classes and integrating them into your project.
Configure the Protoc Output Directory:
- Modify the protoc command to specify a custom output directory that aligns with Gradle's classpath. This approach requires manual intervention during the build process.

Debugging and Additional Tips

Check Your Build File: Double-check your build.gradle file for any typos or misconfigurations in the protobuf plugin or dependencies.
Verify Protoc Generation: Ensure the protoc compiler is correctly installed and generating the Java classes in the desired location.
Clean and Rebuild: Performing a clean build and rebuild of your project can sometimes resolve the issue.
IDE Invalidation: If the problem persists, try invalidating and restarting your IDE.

Conclusion

Gradle's inability to find protobuf generated classes is a common hurdle for Android developers using DataStore. By understanding the underlying cause and implementing the solutions outlined above, you can overcome this challenge and enjoy the benefits of using Protobuf in your Android applications.