Arrow Keys

Figure 10-12 Arrow keys

Appropriate Uses for the Arrow Keys

Arrow keys are never used to duplicate the function of the scroll bars or to move the mouse pointer. They may be used as a shortcut to move the insertion point and, under some circumstances, to make selections.

An application should use the arrow keys only when appropriate to the task. Applications that deal with text or arrays, such as word processors, spreadsheets, and databases, have an insertion point. This insertion point could be moved both by the mouse and by the arrow keys.

If the user makes a selection and then presses the Right Arrow or Left Arrow key, your application should shrink the selection to zero length and place the insertion point at the right or left edge of the selection. This action doesn't move the location of the selection.

In a graphics application, the arrow keys can be used for fine movement of selected objects, particularly since graphics applications typically have no insertion point. If a graphics application uses arrow keys, it should be only to move the selected object by the smallest possible increment (one pixel or one grid unit). For example, the user could select an object and use the arrow keys to move one pixel per keystroke in the direction of the arrow key pressed. Generally, graphics applications shouldn't use arrow keys to change a selection or use modifier keys to multiply the effect of arrow keys. (Note that the Finder uses arrow keys to change the selection.)

Moving the Insertion Point

During vertical movement of the insertion point, horizontal screen position is maintained in terms of screen pixels, not characters. (Character boundaries seldom line up vertically when proportional fonts are used.) When the insertion point moves to a new line, move it slightly left or right, to the nearest character boundary on the new line. During successive movements up or down, the application should keep the insertion point as close as possible to the original horizontal position as it moves from line to line.

Moving the Insertion Point in Empty Documents

Other applications treat an empty document as a page of space characters, in which case clicking at the bottom of a blank screen puts the insertion point where the user has clicked and lets the user type characters there, overwriting the spaces. In this sort of application, Down Arrow moves the insertion point straight down through the spaces. Whichever of these methods you choose for your application, it's essential that you be consistent throughout.

Using Modifier Keys With Arrow Keys

You can support using modifier keys with arrow keys to move the input focus, extend a selection, or move objects. The most common uses of these keyboard combinations are to extend selections and to move the insertion point. The paragraphs that follow suggest typical uses for modifier key-arrow key combinations.

The Option key and the Command key are both used as semantic modifiers with the arrow keys. A semantic modifier changes the semantic unit that the arrow keys affect. The application determines what the semantic units are. For example, in word-processing applications, semantic units are characters, words, lines, paragraphs, and documents. In general, the Option key increases the size of the semantic unit by 1 compared to the arrow keys alone, and the Command key enlarges the semantic unit again. Table 10-2 shows how the Option key and Command key could change the effect of arrow keys in a word-processing application.

Table 10-2 How modifier keys change the movement of the insertion point with the arrow keys

	Arrow key alone	With Option key	With Command key or Shift key
Left Arrow	Left one character	Left one word	To beginning of line
Right Arrow	Right one character	Right one word	To end of line
Up Arrow	Up one line	To start of paragraph	To top of window
Down Arrow	Down one line	To end of paragraph	To bottom of window

If there aren't any paragraphs or an additional paragraph marker after the insertion point in the document, then Option-Down Arrow can't move the insertion point to its end. In this case, you should map Option-Down Arrow to have the same action as Down Arrow. For example, if the insertion point is already at the end of the document and the user presses Option-Down Arrow, play the system beep to call the user's attention to the position of the
insertion point.

In an application (such as a spreadsheet) that represents data in an array, the basic semantic unit would be the cell. Option-Left Arrow (or Option-Right Arrow) would designate the cell to the left (or right) of the currently active cell as the new active cell. Using modifier keys with arrow keys doesn't change the data; Option-Left Arrow just causes the data to be entered and moves the selection to the next cell to the left.

Though the use of multiple modifier-key combinations (such as Command-Option-Left Arrow) is discouraged, it's all right to use the
Shift key with any one of the other modifier keys for making a selection.
(See "Selecting With the Arrow Keys" on page 293 for more information.)
If multiple keys must be pressed simultaneously, they should be fairly close together, otherwise, some people won't be able to use that combination.

Note that for non-Roman script systems, Command-Left Arrow and Command-Right Arrow are reserved for changing the direction of keyboard input. Specifically, Command-Right Arrow changes the keyboard layout to Roman and Command-Left Arrow changes the keyboard layout to the system script. This capability is especially useful for bidirectional script systems such as Arabic and Hebrew since it allows users to change the direction of keyboard input. See Table 4-2 in Chapter 4, "Menus," on page 102 for more information. Also, Command-Shift-Left Arrow and Command-Shift-Right Arrow move the insertion point to the beginning and end of the line, respectively.