Back

From MobileDesign

Mobile applications have two ways to use the Back function: as a breadcrumb or history list, or as a path home. This article discusses these two approaches, and back as a general navigation methodology.

[edit] Back as history

Say I am in the phonebook and I click an address. The map opens. In the map I do a search and the search result includes an email address. I click it, the email editor opens and I send an email.

I have jumped from "application" to "application" in the phone. How do I want the Back function to work? I'd want to backstep from the email to the map to the phonebook. This breadcrumb-like (or trackback) history trail is the behavior many users are accustomed to from internet browsers.

[edit] Back as "A path home"

On many phones the Back key does not step back through a history. It takes the user back or up one level, either to the main menu or to the idle screen. The advantage is that users never get lost and can fairly quickly get back to known territory.

[edit] The Home key

A prerequisite for the history stack approach is that the phone has a "Home" key. You don't want the user to have to press Back 20 times to get to the main menu. In addition to WinMob, Android and the iPhone uses a hardware Home key. Btw: In version 6 Windows Mobile changed the back behavior from "A path home" to a history stack.

Some devices have a logical home key by allowing direct exit of an application, either via a softkey, or as a softkey menu option; the idle screen is the default view when exiting an application. On many devices, pressing the end/hang-up key will act as an exit function, and therefore a logical home key. Some of these use it as a "super back" key, so require more than one keypress to return home.

If you want to have a history function in your application (assuming your application is large and/or deep), and the phone does not have a hardware Home key, what are your options? Your only choice is to give the right softkey double or triple duty as Back + Home or Clear + Back + Home key. It is doable, but has to be thought out carefully and it may not be worth the trouble.

[edit] How Back works in Browsers

Current Internet browsers use a stack to implement the Back and Forward button behavior: the effect is that a person can use these buttons to move up and down the single hierarchical path captured by the stack, but cannot use it to revisit any pages that branched off that path as these are popped off the stack.

To illustrate this problem, let us take a person who starts at page A and visits page B. He then clicks the Back button to return to page A, then visits page C. This navigation path can be shown as A → B ï A → C. The contents of the Back menu will now be {A,C}. Page B has been pruned out of the menu entirely. (source)

This behavior corresponds poorly to the mental model of most people. Most people incorrectly believe that the Back button models a history list of all pages visited. It may seem that this system is confusing and frustrating, but research reveals no major problems with stack based navigation! An advantage of Back navigation is that it represents a very light cognitive load. People tend to use a simple "click until the desired page is recognized" strategy, and are happy to trade "true back navigation" for this simple model.

Techniques more sophisticated than the stack could be employed, but the simplicity and the effect of conditioning from a decade of browser use, dictates that the Back navigation functionality should mimic the one seen in Internet web browsers.

[edit] Don't store everything

The following states in the UI should not generally be included in the history stack:

• Notifications
• Confirmation dialogs and pop-up like states
• Sign-on or other types of password-entry screens

[edit] The Back key

The right softkey is default back navigation. The ultimate Back (from the application perspective) is an exit to the idle state, (closing of the application). In this case the right softkey is labeled Exit instead of Back.

Many Sony Ericsson phones have a hardware Back key. Some phones have a Clear key that does double duty as Clear and Back key. The preferred behavior is that the control keys work the same way in the application as they do in the phone OS.

And note: Back navigation cannot be used as an Undo function. After backstepping to the previous page, the screen should look the same as before. The focus must be returned to the same items, and items kept in the same positions on the screen. However, any data that is committed will not and should not be undone by "Back". An Undo function must be labeled "Undo" and must be UI widget-oriented and not page-oriented.