Apple 2 manual Universal Scroll Arrows

C H A P T E R 2

Container Views

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

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.

2-38 How Views Work