C H A P T E R 9

User Input

Using the Mouse

Just moving the mouse changes only the pointer’s location, and possibly its shape. Pressing the mouse button indicates the intention to do something, and releasing the mouse button completes the action. Pressing by itself should have no more effect than clicking does, except in well-defined areas, such as scroll arrows, where it has the same effect as repeated clicking. For example, pressing a Finder icon should select the icon but not open it.

The mouse devices provided with Macintosh computers have only one button, and these guidelines apply to single-button mice. Other input devices may include additional buttons that can be programmed to replicate functionality provided in Mac OS X through keystrokes.

Clicking

Clicking has two components: pushing down on the mouse button and releasing it without moving the mouse. (If the mouse moves between button down and button up, it’s dragging, not clicking.)

The effect of a click should be immediate and obvious. If the function of the click is to cause an action (such as clicking a button), the selection is made when the button is pressed, and the action takes place when the button is released. For example, if a user presses down the mouse button while the pointer is over an onscreen button, thereby putting the button in a selected state, and then moves the pointer off the button before releasing the mouse button, the onscreen button is not clicked. If the user presses an onscreen button and rolls over another button before releasing the mouse, neither button is clicked.

Double-Clicking

Double-clicking involves a second click that follows immediately after the first click. If the two clicks are close enough to each other in terms of time (as set by the user in Mouse preferences) and location (usually within a couple of pixels), they constitute a double click.

Double-clicking is most commonly used as a shortcut for other actions, such as pressing Command-O to open a document or dragging to select a word. Because not everyone is physically able to perform a double click, it should never be the only way to perform an action.

164The Mouse and Other Pointing Devices

Apple Computer, Inc. June 2002

C H A P T E R 9

User Input

Some applications support triple-clicking. For example, in a word processor, the first click sets the insertion point, the second click selects the whole word, and the third click selects the whole sentence or paragraph. Supporting more than three clicks is inadvisable.

Pressing

Pressing means holding down the mouse button while the mouse remains stationary. Pressing certain objects, such as scroll arrows, has the same effect as repeatedly clicking the object.

Dragging

Dragging means pressing the mouse button, moving the mouse to a new position, and releasing the mouse button. The uses of dragging include selecting blocks of text, choosing a menu item, selecting a range of objects, moving an icon from one place to another, and shrinking or expanding an object.

Dragging a graphic object should move the entire object (or a transparent representation of it), not just the object’s outline.

Your application can restrict an object from being moved past certain boundaries, such as the edge of a window. If the user drags an object and releases the mouse button outside the boundary, the object stays in the original location. If the user drags the item out of the boundary and then back in before releasing the mouse button, the object moves to the new location. Your application can also automatically scroll a document if the user moves an object beyond the boundary of a window (see “Automatic Scrolling” (page 87)).

Also see “Drag and Drop” (page 219) for some more information about dragging and automatic scrolling.

Apple Computer, Inc. June 2002