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Android Components > Concept > Engine

The concept-engine component contains interfaces and abstract classes that hide the actual browser engine implementation from other components needing access to the browser engine.

There are implementations for WebView and multiple release channels of GeckoView available.

Other components and apps only referencing concept-engine makes it possible to:

  • Build components that work independently of the engine being used.
  • Build apps that can work with multiple engines (Compile-time or Run-time).
  • Build apps that can be build against different GeckoView release channels (Nightly/Beta/Release).


Setting up the dependency

Use Gradle to download the library from (Setup repository):

implementation "org.mozilla.components:concept-engine:{latest-version}"


Usually it is not needed to interact with the Engine component directly. The browser-session component will take care of making the state accessible and link a Session to an EngineSession internally. The feature-session component will provide "use cases" to perform actions like loading URLs and takes care of rendering the selected Session on an EngineView. ``

Observing changes

Every EngineSession can be observed for changes by registering an EngineSession.Observer instance.

engineSession.register(object : EngineSession.Observer {
    onLocationChange(url: String) {
        // This session is pointing to a different URL now.

EngineSession.Observer provides empty default implementation of every method so that only the needed ones need to be overridden. See the API reference of the current version to see all available methods.


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