title: How to keep SD card folder sync as like dropbox/Google drive do
body: <p>Hello I am learning how dropbox, Google Drive app always keep sync everything in a very nicely way. I want to learn from those how actually they are doing.</p>
  
  <p>I have this approach to do same like create a database in the app. Once a user add a file into that folder then add that file info in the database and uploaded status as well.</p>
  
  <p>At the same when any file is added/updated/deleted then update status of uploaded and start to upload the file.</p>
  
  <p>I'm not sure if I am wrong in this approach, please guide you guys may know more about this sure.</p>
  
  <p>And I want to know how dropbox app keep SD card folder of my android phone always sync even when I delete the any file of that folder from anywhere like browser.</p>
  
  <p>Whenever user delete any file from browser or anywhere then at the same time, dropbox remove that file from that folder in my SD card. How they are doing this ? Are they using using push notification system or running service in a gap of 1 seconds to know whether any files is updated/added/deleted.</p>
  
  <p>Thanks in advance.</p>