Projectile for multiple projects

[Shiyuan]

Hi all,
     ` helm-projectile-find-file` seems only find files  in the current
project.  Say that I want to open a file in one of the projects in the
known-project list, I need to switch to each project and run
helm-projectile-find-file for each project. If there are three or more
projects in the known-project list, my way is not efficient.   Is there an
easier way? Thanks.

Shiyuan