CUP OF TEA TEST

Aus DPWiki - The Design Pattern Wiki

Illustration

When getting on or off a bus, users have to interrupt their work on their handheld device. Thus applications should be designed that users can safely be interrupted without destroying any data.

Context

…you want to design a MOBILE APPLICATION for a handheld device. As those devices are mostly used in-between other activities, users may get interrupted while working with an application.

Problem statement

What happens when the user goes for a cup of tea and turns the device off while your application is still running?

Problem description with forces

Typically pocket users expect to be interrupted more in their tasks, since they can use their systems anywhere. They're not at a desk, they get off a bus and have to put the computer away!

What happens if they were in the middle of a complex operation when they turned the machine off?

While desktop applications have a lot of screen real-estate devoted to showing the user context (title bar, toolbars, status bars etc), pocket systems cannot afford this real-estate.

Examples

Palm OS provides means to show users what they were doing before they were interrupted.

For example, on a Palm with a menu popped up from a dialog (a), switching the machine off and on (or letting it time out) will remove the popup menu from the screen, but leave the dialog, without making any changes to the dialog's state (b). While switching to another application, then switching back again will remove both menu and dialog, restarting the application as if nothing had happened (c).

Microsoft Windows powered Pocket PC and Smartphone devices rely on an auto-save model, in which data is saved as soon as the user enters it into an entry field [1].Using this approach, there is no data loss when the user switches applications or turns off the device.

Solution

Therefore:

Design all screens to make the state of the system clear at all times.

For any screen or dialog, imagine the user leaves it to go away for a cup of tea, and comes back having forgotten what she was doing. Would it still make sense? If not, add status information into the screen so that users will be clear what they were doing when they return from the interruption.

Alternatively, return the system to a safe state, so that they will not inadvertently destroy any of their data.

Diagram

References

This is a basic pattern and has no further references in this pattern language.

Notes

This pattern was adopted from Charles Weir and James Noble [2]. It was modified to be adapted to the structure and format of this pattern language and supplemented where necessary.

Literature and Links

1. Microsoft Corporation (July 2003). Pocket PC User Interface Guidelines http://msdn.microsoft.com/library/en-us/ui_guide_ppc/htm/Auto_Save.asp <LI>Weir, C. and Noble, J. (2001): A window in your pocket - Some small patterns for user interfaces. In Proceedings of the European Conference on Pattern Languages of Program Design, EuroPloP 2001. The Hillside Group, Inc. </OL>