externalFilesDir property
Returns the absolute path to the directory on the primary shared/external storage device where the application can place persistent files it owns. These files are internal to the applications, and not typically visible to the user as media.
Implementation
static Future<Directory> get externalFilesDir async {
assert(Platform.isAndroid);
return Directory(
await _channel.invokeMethod('getExternalFilesDir') as String);
}