openFd, is obtained from

PluginRegistry.Registrar or

FlutterView.

As an example, suppose you have specified the following
in your pubspec.yaml

flutter

assets

icons/heart.png

This reflects the following structure in your Flutter app.

To access icons/heart.png from your Java plugin code,
do the following:

AssetManager

assetManager

registrar

context

().

getAssets

();

String

key

registrar

lookupKeyForAsset

"icons/heart.png"

);

AssetFileDescriptor

fd

assetManager

openFd

key