Extending Anvil for Fun and Profit

Extending Anvil for Fun and Profit

摘要

We use Dagger heavily in the Slack Android app for compile-time dependency injection. It’s powerful, flexible, supports basic Kotlin idioms, and allows for advanced dependency injection patterns with less boilerplate. It’s not without its sharp edges though. It slows down our builds with kapt, has a steep learning curve, and can often be tedious to write out its module+component plumbing.

Anvil augments Dagger’s own boilerplate. Factory generation enables us to remove kapt from much of our project, @ContributesTo and @ContributesBinding allow us to automatically wire dependencies without modules, and @MergeComponent allows us to automatically wire together component interfaces. Factory generation alone recently helped us reduce our incremental build times by as much as 25%!

Anvil’s core features are fantastic, but they are not (nor pretend to be!) turnkey solutions for every use case, though they cover the common ones. Every codebase has its own patterns and nuances, so Anvil 2.3.0 introduced a new compiler-api artifact that allows us to extend Anvil’s own code generation to suit those remaining needs. In this post we’ll detail a little of how it works with our own Activity injection pattern as an example.