There are 100s of ways to hide stuff, but no one-click way to unhide, that's built-in. Here's a one-line script for unhiding objects; just select the hidden object(s) in schematic view, and hit the button. Its a great time-saver if you use the schematic view to organize 100s of objects.
To install:
Just run the script, then set it as a toolbar button or key binding from the "Ewanc" category.
Update:
Fixed a syntax bug which had broke it initially.
Beware: New (2017+) versions of Max brake the whole schematic view system. You have to go into settings; file options: and turn schematic view saving back on or your save schematic views wont load.