The Pop-up List

Pop-up lists are used in lieu of a series of mutually-exclusive switches.  They save screen space and prevent overcrowding in panels.  Each list is controlled by a button that can be recognized by a special symbol.  The label on the button that precedes the symbol indicates the current selection from the list.  When the user makes a new selection, the button label changes.

Pressing the button pops the list up so that the item matching the button label appears on top of the button.  The list remains up only while the user holds the mouse button down.  When the user releases the mouse button after dragging to a different item in the list, the label on the button changes to that item.

Many times a pop-up list needs a more constant title than the changing button label, and usually this is done by enclosing the pop-up button in a box and titling the box appropriately. 

Arranging Pop-Up Lists

When a panel includes a pop-up list, it's important to pay attention to the look of the panel when the list is popped-up on-screen.  Be sure, for example, that the list doesn't obscure any objects in the panel that provide a context for understanding the content of the list.  Also make sure that the open list doesn't blend in with the panel.  If an item in the list pops up alongside an object in the panel, it might lead users to interpret them in combination.  
A pop-up list usually pops up so that the current selection is under the cursor.  But if the list is long and near the edge of the screen, it shifts so that the entire list can appear on-screen, and this may change the selection under the cursor.  Users might therefore unwittingly make a new selection while intending only to see what's in the list.  You may want to avoid placing a pop-up list where it will deterministly exhibit this behavior.

Pop-up lists have many features in common with a matrix of radio buttons or a scrolling list.  For a comparison of pop-up lists and radio buttons, see the help for ªradio Button.º  For a comparison of radio buttons and pop-up lists, see the help for ªNXBrowser.º