C H A P T E R 7

Controls

Figure 7-26 Tab panes inset from edge of window

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Spaces should be equal.

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Progress Indicators

Progress indicators inform users about the status of lengthy operations. (For guidelines on when to provide such information, see “Feedback and Communication” (page 29)). There are two types of progress indicators:

■Determinate: Use when the full length of an operation can be determined and the user can see how much of the process has been completed. You could use a determinate progress indicator to show the progress of a file conversion, for example.

■Indeterminate: Use when the duration of a process can’t be determined. You might use an indeterminate progress indicator to let the user know that the application is attempting a dialup communication connection, for example, when there’s no way to accurately determine how long it will take to complete. If an indeterminate process reaches a point where its duration can be determined, switch to a determinate progress indicator.

Apple Computer, Inc. June 2002

C H A P T E R 7

Controls

Typical progress indicators look like the bars shown in Figure 7-27. In a determinate progress bar, the “fill” moves from left to right, and should fill in completely before it is dismissed. An indeterminate progress bar displays a spinning striped cylinder to indicate an ongoing process.

Determinate progress bars should associate progress with time. A progress bar that becomes 90-percent complete in 5 seconds but takes 5 minutes for the remaining 10 percent, for example, would be annoying and lead users to think that something is wrong.

Progress indicators typically appear within a progress dialog. When the process being performed can be interrupted, the progress dialog should contain a Cancel button (and support the Escape key). If interrupting the process will result in possible side effects, the button should say Stop instead of Cancel.

142Control Behavior and Appearance

Apple Computer, Inc. June 2002

C H A P T E R 7

Controls

An alternative to the indeterminate progress bar, spinning arrows (see Figure 7-28) can be used when space is very constrained. They are best used for asynchronous events that take place in the background, such as retrieving messages from a server. Don’t use spinning arrows in operations that start out indeterminate but could become determinate.

In Cocoa, spinning arrows are included as an alternate style of the NSProgressIndicator function. In Carbon, the function to create these arrows is

CreateChasingArrowsControl.

Figure 7-28 Spinning arrows used instead of indeterminate progress bar

Don’t use a progress bar to display relevance. Instead, use the relevance control (available in Carbon via the CreateRelevanceBarControl in the Control Manager or DrawThemeTrack in Appearance Manager) shown in Figure 7-29.

Figure 7-29 Relevance control

Apple Computer, Inc. June 2002