https://stackoverflow.com/questions/46698751/permission-denied-at-externalstoragedirectory-access-via-flutter-plugin
https://stackoverflow.com/questions/31162638/grant-permission-required-for-external-storage-in-android-m
https://pub.dartlang.org/packages/permission
https://pub.dartlang.org/packages/simple_permissions
原文：https://www.cnblogs.com/pythonClub/p/10689836.html