NXBrowser 

The NXBrowser class is used to provide the user with a scrolling list of choices.  Pop-up lists and radio buttons can also be used to display a group of options, however, scrolling lists distinguish themselves because they can offer multiple selection.  Unlike radio buttons, scrolling lists and pop-up lists both can have their contents altered dynamically, and both save screen space.  The following considerations enter into the decision whether to implement a control as a pop-up list or as a scrolling list:

·	If it's conceivable that the list could grow to be very large, a scrolling list is the better choice.  The entire contents of a pop-up list must fit on-screen.  Unbounded lists should never be implemented as pop-up lists.  A good example of this is the scrolling list of font families in the Font Panel.  There is no bound on the number of fonts the user could have installed, therefore, a scrolling list is the proper choice.

·	On the other hand, if the list is short or limited, a pop-up list might be the better choice.  Pop-up lists let the user see all the available options on-screen at once.

·	If screen space is limited, a pop-up list might be the better choice.  Scrolling lists take up more room.

·	If the user needs to see at least some of the choices on-screen to understand what's in the list, a scrolling list might be the better choice.  More of the list is always visible.

·	If the user can select more than one item from the list, a pop-up list is inappropriate.

Double-Clicking an Item in a List

Often a panel provides the user with a list of choices (e.g., the Open and Save panels).  Double-clicking an item within the list should perform the same action as pressing the Return key (i.e., the same action as the button marked with the Return symbol).