C H A P T E R 8

User Input

Important:Avoid assigning any key combinations listed in the tables in this section to commands other than those specified in the tables. Even if your application doesn’t support all the keyboard equivalents shown, don’t assign unused combinations to commands that conflict with those specified in this section.

The Functions of Specific Keys

There are four kinds of keys: character keys, modifier keys, arrow keys, and function keys. A character key sends a character to the computer. When the user holds down a modifier key, it alters the meaning of the character key being pressed or the meaning of a mouse action.

Note: Not all the keys described here exist on all keyboards. Don’t depend on a key as the only way for users to accomplish a task. You cannot assume anything about which keyboard (if any) is connected to a computer.

Character Keys

Character keys include letters, numbers, punctuation, the Space bar, and nonprinting characters—Tab, Enter, Return, Delete (or Backspace), Clear, and Esc (Escape). It is essential that your application use these keys consistently.

Space Bar

In text, pressing the Space bar enters a space between characters.

When full keyboard access is turned on, pressing the Space bar selects the item that currently has the keyboard navigation focus (the equivalent of clicking the mouse button).

Tab

In text-oriented applications, the Tab key moves the insertion point to the next tab stop. In other contexts, Tab is a signal to proceed; it means “move to the next item in a sequence.” The next item can be a table cell or a dialog text field. Shift-Tab navigates in the reverse direction. Pressing Tab can cause data to be entered before focus moves to the next item. For more details about navigating with the Tab key, see “Keyboard Focus and Navigation” (page 107)

Enter

Most applications add information to a document as soon as the user enters it. In some cases, however, the application may need to wait until a whole collection of information is available before processing it. The Enter key tells the application that the user has finished entering information in a particular area of the document, such as a text field. While the user is entering text into a text document, pressing Enter has no effect.

If a dialog has a default button, pressing Enter (or Return) is the same as clicking it.

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C H A P T E R 8

User Input

Return

In text, the Return key inserts a carriage return (a line break) and moves the insertion point to the beginning of the next line. In arrays, the Return key signals movement to the leftmost field one step lower (like a carriage return on a typewriter). As with Tab, pressing Return can cause data to be entered before focus moves to the next item.

If a dialog has a default button, pressing Return (or Enter) is the same as clicking it.

Delete (or Backspace)

Generally, if an item is selected, pressing Delete (or Backspace) removes the selection without putting it on the Clipboard. If nothing is selected, pressing Delete removes the character preceding the insertion point without putting it on the Clipboard. The Delete key has the same effect as the Delete command in the Edit menu.

Note:The Delete key is different from the Forward Delete (Fwd Del) key (labeled Del), which removes characters following the insertion point. See “Forward Delete (Fwd Del)” (page 102)

The Option key can be used to extend a deletion to the next semantic unit (such as a word). The Command key can extend a deletion to the next semantic unit beyond that supported by Option. Recommended key combinations for text applications are Command-Delete to delete the previous word and Command–Fwd Del to delete the next word. Option-Delete could delete either the word containing the insertion point or the part of the word to the left of the insertion point, depending on what makes the most sense in your application; Option–Fwd Del could delete the part of the word to the right of the insertion point.

Clear

The Clear key has the same effect as the Delete command in the Edit menu: It removes the selection without putting it on the Clipboard. Not all keyboards have a Clear key, so don’t require its use in your application.

Esc (Escape)

The Esc (Escape) key basically means “let me out of here.” It has specific meanings in certain contexts. The user can press Esc in the following situations:

■In a dialog, instead of clicking Cancel

■To stop an operation in progress (such as printing), instead of pressing Command-period

■To cancel renaming a file or an item in a list

■To cancel a drag in progress

Pressing Esc should never cause the user to back out of an operation that would require extensive time or work to reenter. When the user presses Esc during a lengthy operation, display a confirmation dialog to be sure that the key wasn’t pressed accidentally.

Modifier Keys

Modifier keys alter the way other keystrokes or mouse clicks are interpreted. You should use these keys—Shift, Caps Lock, Option, Command, and Control—consistently as described here.

2008-06-09 | © 1992, 2001-2003, 2008 Apple Inc. All Rights Reserved.

C H A P T E R 8

User Input

Shift

When pressed at the same time as a character key, the Shift key produces the uppercase alphabetic letter or the upper symbol on the key.

The Shift key is also used with the mouse for extending a selection or for constraining movements in graphics applications. For example, in some applications pressing Shift while using a rectangle tool draws squares.

Caps Lock

When activated, the Caps Lock key has the same effect on alphabetic keys as the Shift key, but it has no effect on nonalphabetic keys. When the Caps Lock key is down, the user must press Shift to type the upper character on a nonalphabetic key.

Option

When used with other keys, the Option key produces special symbols. The Keyboard Viewer, which users can add to the Input menu in the International pane of System Preferences, shows which keys generate each symbol.

The Option key can also be used with the mouse to modify the effect of a click or drag. For example, in some applications pressing Option while dragging an object makes a copy of the object.

Command

On most keyboards, the Command key is labeled with a cloverleaf symbol () and an Apple logo (). Pressing the Command key at the same time as a character key tells the application to interpret the key as a command rather than a character. It can also be used with the mouse to modify the effect of a click or drag. Key combinations that use the Command key are described in “Keyboard Shortcuts” (page 103)

Control

The Control key is used to modify the functions of other keys. Combined with a mouse click, it displays contextual menus (see “Contextual Menus” (page 184)).

Control-F7 temporarily overrides a user’s preference for default navigation or full keyboard navigation in windows and dialogs. For more information, see “Keyboard Focus and Navigation” (page 107)

Cocoa: In Cocoa applications, the Control key has additional defined behaviors, as described in “Text System Defaults and Key Bindings” in Cocoa Event-Handling Guide in Cocoa Events & Other Input Documentation.

Arrow Keys

Apple keyboards have four arrow keys: Up Arrow, Down Arrow, Left Arrow, and Right Arrow. They can be used alone or in combination with other keys. Keyboard combinations using the arrow keys should be used only for shortcuts for mouse actions. It is never appropriate to implement only a keyboard combination and not provide a mouse-based way to perform the same action.

Appropriate Uses for the Arrow Keys

You can use arrow keys in these ways:

2008-06-09 | © 1992, 2001-2003, 2008 Apple Inc. All Rights Reserved.

C H A P T E R 8

User Input

■In text, the arrow keys move the insertion point. When used with the Shift key, they extend or shrink the selection. If the user makes a selection and then presses the Right Arrow or Left Arrow key, the selection shrinks to zero length and the insertion point moves to the right or left edge of the selection.

■In lists, the arrow keys change the selection.

■In a graphics application, the arrow keys can be used to move a selected object the smallest possible increment (one pixel or one grid unit).

■In full keyboard access mode, the arrow keys move between values within a control.

Don’t use the arrow keys to:

■Move the mouse pointer onscreen

■Duplicate the function of the scroll bars

Moving the Insertion Point

When the insertion point moves vertically in a text document, its horizontal position is maintained in terms of screen pixels, not characters (in other words, the insertion point could move from the twenty-fifth character in a line down to the fiftieth character, depending on the font and size). As the insertion point moves from line to line, keep it as close as possible to its original horizontal position, moving it slightly left or right to the nearest character boundary.

The Option and Command keys are used as semantic modifiers with the arrow keys. As a general rule, 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. The application determines what the semantic units are. In a word processor, typically the units are characters, words, lines, paragraphs, and documents. In a spreadsheet, a basic semantic unit could be a cell.

Table 8-1 describes the appropriate behavior of the arrow keys in text documents and fields. In some cases, the behavior describes what happens when the indicated keys are pressed more than once in succession.

Table 8-1 Moving the insertion point with the arrow keys

2008-06-09 | © 1992, 2001-2003, 2008 Apple Inc. All Rights Reserved.

C H A P T E R 8

User Input

Note: For non-Roman script systems, Command–Left Arrow and Command–Right Arrow are reserved for changing the direction of keyboard input.

Extending Text Selection With the Shift and Arrow Keys

Table 8-2 describes how to extend text selection by pressing the Shift key with the arrow keys.

Table 8-2 Extending text selection with the Shift and arrow keys

2008-06-09 | © 1992, 2001-2003, 2008 Apple Inc. All Rights Reserved.