How to remap F4 to Dashboard or Notifications on a MacBook Pro in Yosemite?

Solution 1:

Do you have any exclamation points in triangles indicating the key is also mapped to a different function? From what you’ve described as your settings, it should be working…

Solution 2:

I have the same settings described in the message above and I don't get the Dashboard either. I have ended up assigning the top-right corner as a "hot corner" that shows the Dashboard.
System Preferences > Mission control > Hot corners (left-bottom corner of the window).

Solution 3:

System Preferences > Mission Control > Dashboard (drop-down) Change dashboard drop down box from "off" to either "As overlay" or "As space"

Side note: I do have Show Dashboard set as F4 as seen below in this same Mission Ctrl window. Also, I have the same settings as was mentioned in the original posted question.