CHAPTER 2
Container Views
2-38 How Views Work
Each tap on a scroll arrow moves one unit in the chosen direction. Your
application determines how much one unit is. For example, the Notepad
moves one note for each tap on the arrow; for a note longer than the view, each
tap scrolls the number of displayed lines minus one. The Names File application
moves one “card” for each tap. The Date Book’s day-at-a-time view moves one
day for each tap, and the week-at-glance view moves a week per tap. Time
Zones moves from city to city alphabetically. If your application’s information
falls naturally into sections, each tap on a scroll arrow should scroll one section.
If not, scroll a screenful minus one line at a time (a “page”).
Whether your application should scroll smoothly or unevenly depends on the
type of information being scrolled. With smooth scrolling, each tap on a scroll
arrow moves the same amount. That is how the Date Book, Names File,
Calculator, and Time Zones applications work, for example. In some cases,
uneven scrolling is better than smooth scrolling. The Notepad scrolls by
uneven increments—note by note—to take advantage of a user’s visual
memory of where he or she wrote things.
While scrolling up by uneven increments, an application may encounter an
item that is too large to display all at once. Since the application can’t show
the whole item, it must either show the bottom of the item or the top of the
item. The appropriate response depends on whether the view scrolls page-by-
page or continuously like a roll of paper. A view that scrolls continuously
should scroll up to the bottom of an item that is too large to show all at once.
A view that scrolls page-by page should scroll up to the top of an item that is
too large to show all at once. For instance, the Notepad (which scrolls like a
roll of paper) scrolls up to the bottom of a note that is taller than the height of
the Notepad main view. In contrast, the Out Box (which scrolls detail items
page-by-page) would scroll up to the top of the same note.
Universal Scroll Arrows 2
Newton devices have two universal scroll arrows for user control of scrolling.
The universal scroll arrows are part of the Newton system; they are not
attached to one view. On an Apple MessagePad 120, they are located in the
center of the screen, below the display area. Figure 2-31 shows the universal
scroll arrows.