externalCacheDir property
Returns absolute path to application-specific directory on the primary shared/external storage device where the application can place cache files it owns. These files are internal to the application, and not typically visible to the user as media.
See: https://developer.android.com/reference/android/content/Context#getExternalCacheDir()
Implementation
static Future<Directory> get externalCacheDir async {
assert(Platform.isAndroid);
return Directory(
await _channel.invokeMethod('getExternalCacheDir') as String);
}