Note:
  Flutter’s debug/release builds have drastically different
  performance characteristics. To evaluate the performance
  of Flutter, use a release build.

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.

Developers that would like their cached engine to begin
with a custom initial route can configure their cached
FlutterEngine to use a custom initial route just before
executing the Dart entrypoint. The following example
demonstrates the use of an initial route with a cached engine:

Java

Kotlin

public

class

MyApplication

extends