Why is my Launchpad missing app icons? Sometimes my Launchpad just look like this without any app icons. What causes this problem and how can I solve it?

I am using 2011 11″ MacBook Air with OS X 10.9.1
This didn't work for me,
Finder did not respond, clicking on Apps gave this error  

Could not obtain valid temporary directory for sandboxed app ...


I also had to open a terminal and run:

cd /var/folder
sudo rm -rf *


Searched for and opened Activity Monitor, stopped the com.apple.IconServicesAgent service and rebooted.

My icons came back in launchpad and dock.