C H A P T E R 3

Human Interface Design

Extending the Interface

This section describes how to extend the Mac OS X user interface when your application requires an element or a behavior that doesn’t already exist. When a need arises that can’t be met by the standard elements, you can extend the set of controls using these guidelines, provided that the new element or behavior supports Apple’s interface design principles. This section contains information on how to determine when it’s appropriate to go beyond the guidelines, how to use the existing interface elements to build new elements, and what to avoid when you design additional interface elements.

Build on the Existing Interface

People rely on the standard Mac OS X user interface for a consistent, predictable user experience. Don’t copy other platforms’ user interface elements or behaviors in Mac OS X, because they may confuse users who aren’t familiar with them.

If you need to extend the interface of Mac OS X, the best place to begin is with the already defined visual and behavioral language. Think about what the appearance communicates to people (the look) and how they expect the element to behave (the feel).

Visual cues, such as the arrow on a pop-up menu, help people recognize familiar elements. People learn to associate certain behaviors with specific elements based on their appearance. For example, people recognize push buttons by their rounded shape and look for a label that identifies the action the button causes. This particular appearance distinguishes a push button from other types of elements. When people click a button, they expect it to be highlighted to indicate that the action took effect, and they expect the action to take effect immediately. People may also expect that clicking a button will have additional behaviors related to it, such as dismissing a dialog or changing the content area of the active document.

Don’t Assign New Behaviors to Existing Objects

When you use existing interface building blocks, use them in the standard way. Make sure you do not change the behavior of standard elements. When you need a new behavior, design a new element for it. If elements behave differently in different situations, the interface becomes unpredictable and therefore harder to figure out. This can adversely affect the user’s confidence in your application.

Create a New Interface Element Cautiously

Be very cautious about creating new interface elements because you may introduce unnecessary complexity. You will have to work extremely hard to make sure that any newly introduced elements fit in with those provided by Cocoa and Carbon. Additionally, as the Aqua user interface continues to evolve, your custom elements will require updating to adapt to changes in Aqua.

Before implementing a new interface element,makesure that you can’t use existing elements or a combination of them to achieve the desired result. Usability testing is essential for determining whether a new element works.

Extending the Interface

51

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

C H A P T E R 3

Human Interface Design

52	Extending the Interface

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