code: public Intent getPreviewFileIntent(Context context, String path, String lastRev) {
          // TODO(jiuyangzhao): Assert path is valid
          Intent previewIntent = new Intent(ACTION_SHOW_DROPBOX_PREVIEW);
          addExtrasToIntent(context, previewIntent);
          previewIntent.putExtra(EXTRA_DROPBOX_PATH, path);
          previewIntent.putExtra(EXTRA_DROPBOX_REV, lastRev);
  
          if (getDropboxAppPackage(context, previewIntent) == null) {
              return null;
          }
          return previewIntent;
      }
docs: Display the DropboxApp's preview of file located at path This function should only be called
  if file was opened through DropboxAPI. If path refers to a directory (as defined by having a '/' at end,
  will show Dropbox file tree.
  
  <p>You won't need to use this unless you are our official partner in openwith.</p>
  
  @param path    path of file in authorized user's Dropbox to preview
  @param lastRev The revision of file user is seeing (as returned by
  DropboxAPI.getFile/DropboxAPI.putFile)
  @return Intent that when passed into startActivity() displays Dropbox preview Returns null if
  DropboxApp is not installed