我怀疑您正在运行Android 6.0 Marshmallow(API 23)或更高版本.在这种情况下，您必须实施运行时权限，然后尝试读取/写入外部存储.

I suspect you are running Android 6.0 Marshmallow (API 23) or later. If this is the case, you must implement runtime permissions before you try to read/write external storage.