第2个回答 2009-06-08
Mobile applications should rely network connectivity as little as possible
Error prevention and simple error handling
Nothing potentially harmful should be triggered by too simple an operation (e.g., power on/off)
Reduce short-term memory load
Rely on recognition of function choices instead of memorization of commands
Use modalities such as sound to convey information where appropriate
MODIFICATIONS TO EXISTING RULES
The remaining four guidelines require modifications and/or an increased emphasis on use with
mobile devices. These are summarized in Table 2, along with some practical suggestions.
Consistency
Consistency takes on an additional dimension with mobile applications: the consistency across
multiple platforms and devices for the same application [2]. Users of mobile devices may need to
switch between their desktop machines and different mobile devices frequently. For example, a
user may want to transfer some documents from a home desktop computer to a PDA, read them
while riding the subway, and call colleagues with questions. In this situation, consistency should
be maintained between desktop and PDA (and possibly cell phone). Consistency can also be
achieved by creating I/O methodologies that are device independent. Isokoski and Raisamo
proposed a Minimal Device Independent Text Input Method that can be used consistently across
Table 2: Guidelines that need modification
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devices [10].
Reversal of Actions
Allowing easy reversal of actions may be more difficult for mobile devices because of a lack of
available resources and computing power [12]. Mobile devices have less memory to store the
states of past events. Even if state information is offloaded to more powerful stationary
computers, the greater susceptibility of wireless communications to connectivity losses makes
tracking of past states more difficult [12] [8].
Error Prevention and Simple Error Handling
Preventing and handling errors on mobile interfaces are similar to those for desktop interfaces,
although the need becomes more critical due to the more rapid pace of events in the mobile
environment. Error prevention also needs to take the physical design of mobile devices into
account. Smaller device sizes make the proximity of buttons to each other more of a potential
problem.
Reduce short-term memory load
Given the limitations of a user’s short-term memory, interfaces should be designed such that
very little memorization is required during the performance of tasks [2]. When in the mobile
environment, a user has to potentially deal with more distractions than with a desktop computer
[15]. A mobile application may not be the focal point of the user’s current activities [5], and auser may not be able to suspend his or her primary task to interact with the mobile device [3] [8].
Using alternative interaction modes such as sound can be beneficial [11].
Design for multiple and dynamic contexts
Allow users to configure output to their needs and preferences (e.g., text size, brightness)
Allow for single- or no-handed operation
Have the application adapt itself automatically to the user’s current environment
Design for small devices
Provide word selection instead of requiring text input
Design for limited and split attention
Provide sound and tactile output options
Design for speed and recovery
Allow applications to be stopped, started, and resumed with little or no effort
Application should be up and running quickly
Design for “top-down” interaction
Present high levels of information and let users decide whether or not to retrieve details
Allow for personalization
Provide users the ability to change settings to their needs or liking
Design for enjoyment
Applications should be visually pleasing and fun as well as usable
ADDITIONAL GUIDELINES FOR MOBILE DEVICE DESIGN
What follows are additional guidelines specifically for mobile device interface design. Following
these can be critical due to the particular characteristics of mobile devices [12] [3]. Mobile
Table 3: Additional guidelines for mobile interface design
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device interface design is more restrictive than desktop interface design because of relatively
limited computing and communication power, smaller platform sizes, an always-changing
context [15], and smaller amounts of user attention [3]. These guidelines are summarized in
Table 3, along with some practical implementation suggestions.
Design for multiple and dynamic contexts
The contexts of computer applications used in the office, home, or similar settings are relatively
stable. On the other hand, with mobile applications, there can be a significant number of
additional people, objects, and activities vying for a user’s attention aside from the application or
computer itself [15]. Environmental conditions (e.g., brightness, noise levels, weather) can
change depending on location, time of day, and season. The usability or appropriateness of an
application can change based on these different context factors [7]. For example, in the presence
of strangers, users may feel uncomfortable speaking input aloud, and certain places (e.g.,
libraries) might restrict the use of voice input. Small text sizes may work well under office
conditions but suddenly become unreadable in bright sunshine or in dimly lit spaces. In addition,
users may have one hand, or even both hands, occupied while using a mobile device [8].
Therefore, for different contexts, allowing operations with 0, 1, or 2 hands becomes extremely
important to the viability of the interface [7].
One way to solve the problem of changing contexts is to implement context-awareness and
self-adapting functionalities [4]. This can potentially save the user effort and frustration, and
increase the usability of applications. Usability in a dynamic environment might also be
improved by devices that derive input indirectly from the user. Schmidt discussed a vision of
mobile computing where devices can “see, hear, and feel.” [13].
Design for Small Devices
As technology continues to advance, mobile platforms will continue to shrink in size and include
items such as bracelets, rings, earrings, buttons, and key chains. New or modified interaction
techniques may be necessary to overcome the physical limitations. Speech input is a viable
alternative for devices too small for buttons. Sound can also be used for output, taking the place
of text or graphics. Holland and Morse investigated an audio interface for a navigation system
that leaves a user’s eyes and hands free for other purposes [5].
Design for Limited and Split Attention
Users of mobile devices often need to focus on more than one task [8]. A mobile application may
not be the focal point of the user’s current activities [5]. Mobile devices that demand too much
attention may distract users from more important tasks. Interfaces for mobile devices need to be
designed to require as little attention as possible [11]. Sometimes this can be accomplished by
designing for hands-free interaction or even eyes-free interaction. According to Gorlenko [3],
eye-free interaction provides the greatest freedom of movement during interaction, as visual
attention constrains body movement. When possible, it might work better to use sound or tactile
output to present information instead of visual displays [11]. Pascoe, Ryan, and Morse developed
a personal digital assistant (PDA) application, which allowed the user to count the number of
bites taken from tree leaves without looking away from the animal.
Design for speed and recovery
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For mobile devices and applications, time constraints need to be taken into account in initial
application availability and recovery speed. When time is critical, waiting a few minutes for an
application to start may not be in the user’s best interest. Given the different contexts under
which mobile devices are used, users may need to quickly change or access functions or
applications [11]. When such situations rise, a user would need to quickly and securely save any
work already performed and resume it later without any loss.
Design for “Top-Down” Interaction
Mobile devices with small screens have limitations on the amount of information that they can
present at one time. Reading large amounts of information from such devices can require large
amounts of scrolling and focused concentration. To reduce distraction, interactions, and potential
information overload, a better way of presenting information might be through multilevel or
hierarchical mechanisms [1]. For example, a mobile worker may not need or want the entire
contents of a message. However, they may wish to receive a notification that a message is
available, along with an indication of how important it is. That way, the worker can make their
own decision, whether or not to stop their primary task to access the contents of the message.
Allow for personalization
Mobile devices, by their nature, are more personal. While traditional telephones and desktop
computers can many times be shared among different users, a mobile device is usually carried
and used by only one person. Therefore it is more likely that a user of mobile applications will
personalize the device and its applications to his or her preferences. Different users have
different usage patterns, preferences, and skill levels. So it is important to allow for variations
among users. For example, when visibility is good, it is reasonable to show more text on a screen;
and while in a dark environment, bigger fonts might allow better readability. But the interface
design should not exclude the possibility that some users may always prefer larger fonts
regardless of the lighting conditions
Design for Enjoyment
While functionality and usability are keys to mobile application success, other factors are also
influential. Aesthetics is also part of designing an overall enjoyable user experience with mobile
devices. Karlsson and Djabri have begun to investigate “aesthetics in use”[6], which they define
as dynamic interaction that invokes a positive affective response from the user. In addition, color
and its manipulation are important considerations for visual interfaces. Shneiderman gave some
interface color use guidelines that can generally be carried over to mobile devices [14], although
some of the effects of color may be different on smaller screens. If functionality and usability are
equal, an application or device will stand out if it is attractive in some way. Donald Norman,
after years of stressing product design that focuses squarely on usability, realizes that emotion
plays a large part in our interaction with objects [9].
CONCLUSION
This paper has presented a first attempt at a set of guidelines for the design of handheld mobile
device interfaces. These guidelines are based on traditional guidelines for desktop user interfaces
and published research with mobile devices and applications. These guidelines should be useful
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to practitioners who develop mobile applications, and to HCI researchers working with mobile
interface design and usability. Our unique contributions are that we propose a complete set of
guidelines for mobile interface design, and we also draw certain emphasis on some interesting
mobile usability issues.
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