C H A P T E R 9

User Input

Type-Ahead and Auto-Repeat

If the user types faster than the computer can handle or when the computer is unable to process the keystrokes, the keystrokes are queued for later processing. This queuing is called type-ahead. There is a limit (varying with the computer) to the number of keystrokes that can be queued, but it’s usually not reached unless the user types while the application is performing a lengthy operation.

When a character key is held down for a certain amount of time, it starts repeating automatically. The user can make adjustments to this feature, called auto-repeat, in Keyboard preferences.

An application can tell whether keystrokes are generated by auto-repeat or by the same key being pressed numerous times. Your application can disregard auto-repeat keystrokes; it should ignore them in keyboard equivalents.

Auto-repeat works only when the application is ready to accept keyboard input; it does not function during type-ahead.

Selecting

Before performing an operation on an object, the user must select it to distinguish it from other objects. There is always immediate visual feedback to show that something is selected.

Selecting an object never alters the object itself, and a selection is always undoable by clicking outside the selection.

How something is selected depends on what it is. It’s useful to distinguish among three types of objects that are each dealt with in a different way when selected:

■Text. An application considers all text appearing together in a particular context as a block of text—a one-dimensional string of characters. A block of text can range from a single field, as in a dialog, to an entire document, as in a word processor. Regardless of where it appears, text is edited in the same way.

■Arrays are tabular arrangements of fields. A one-dimensional array is a list and a two-dimensional array is a table. Each field contains information such as text or graphics.

Apple Computer, Inc. June 2002