).

build

()

FlutterFragment internally knows about FlutterEngineCache
and retrieves the pre-warmed FlutterEngine based on the ID
given to withCachedEngine().

By providing a pre-warmed FlutterEngine,
as previously shown, your app renders the
first Flutter frame as quickly as possible.

Initial route with a cached engine

The concept of an initial route is available when configuring a
FlutterActivity or a FlutterFragment with a new FlutterEngine.
However, FlutterActivity and FlutterFragment don’t offer the
concept of an initial route when using a cached engine.
This is because a cached engine is expected to already be
running Dart code, which means it’s too late to configure the
initial route.