https://qooah.com/2012/12/25/android-%e7%89%88-dropbox-%e6%9c%89%e6%96%b0-beta-%e6%8e%a8%e5%87%ba%ef%bc%8c%e6%94%b9%e5%96%84%e7%85%a7%e7%89%87%e5%8a%9f%e8%83%bd%ef%bc%81/