What is arouter?

ARouter is a Java library from Alibaba that solves a navigation problem common in large Android apps: when an app is split into many separate modules, those modules cannot directly reference each other's screens without creating tight, hard-to-maintain dependencies. ARouter provides a routing layer that lets any module jump to any screen (called an Activity or Fragment in Android) using a simple path string, like "/account/login", without the two modules needing to know anything about each other's code. The way it works is straightforward. A developer puts a short annotation above each screen class, declaring what path that screen lives at. When another part of the app wants to navigate there, it calls ARouter with that path string and passes along any needed data. ARouter finds the right screen and opens it. This decoupling is particularly valuable when a codebase is split across a team: the payments module can navigate to the profile module without importing any of the profile module's code directly. Beyond basic navigation, ARouter supports interceptors: pieces of code that can run before a navigation happens. A common use case is checking whether a user is logged in before allowing them to reach a restricted screen, then redirecting to a login page if they are not. Interceptors can also be used for analytics or other cross-cutting concerns. The library also handles deep links, meaning it can parse a URL arriving from a web browser or notification and automatically route the user to the right in-app screen, filling in any parameters found in the URL. It supports dependency injection, which is a technique for providing components with the objects they need without those components having to construct those objects themselves. ARouter works with both Java and Kotlin on Android, and there is an Android Studio plugin available that adds a clickable icon next to navigation calls so you can jump directly to the destination screen in your editor.