Home > Articles > Programming

Designing Mobile Interfaces

  • Print
  • + Share This
Now that modern handheld computers (including smartphones) are running real operating systems, it's tempting to port existing software to run on them. David Chisnall discusses how to avoid the pitfalls of moving desktop user interfaces to mobile devices.
Like this article? We recommend

Like this article? We recommend

Modern handheld computers, including mobile phones, are very powerful machines. A latest-generation smartphone has a faster CPU and GPU, and more memory and storage space, than the desktop computer that I took to university. Something like the N900 has higher specs in nearly every respect, including network speed, except for one—screen size.

Because these machines are so powerful, they typically run something like a modern desktop OS. Android uses the Linux kernel. The iPhone uses the XNU kernel. Meego, the platform with the stupid name, uses almost the same software stack as a desktop Linux system, right up to X11 and the toolkits used for GUI programming. Both Symbian and Windows Mobile include all of the features that you'd expect from a modern operating system. Modern handhelds no longer run simple embedded operating systems.

Apple's iPhone uses almost the same stack as an Apple desktop. It differs significantly from desktop OS X in one framework, however: The Application Kit (AppKit) is replaced by the UIKit on the iPhone. Apple had two reasons for making this change:

  • By breaking backward compatibility, Apple could update some of the design decisions that NeXT had made for AppKit back in 1988—approaches that no longer made sense with modern hardware.
  • The more important reason for this change was that switching from the AppKit to the UIKit prevented developers from recompiling Mac applications for the handheld platform.

A Mac application and an iPhone application can still share most of their code, but they must have different user interfaces. This fact is irritating for developers and ideal for users, because a good user interface on the desktop is often a terrible UI on something like a phone. In this article, we'll take a look at some of the differences.

Touch and Go

One of the common rules that apply when designing a user interface is Fitts' Law, which describes the cost of moving a pointer to a target area. The time taken is dependent on both the distance and the size of the target, with the former defining the movement time and the latter defining the stopping time.

It's tempting to think that this rule doesn't apply to a touchscreen, but that's misleading. Moving a finger takes time, just as moving a mouse does—but now you need to perform the calculations in three dimensions.

There are some obvious effects to this difference. For example, with a mouse or a trackpad, a pointer movement and a drag take the same amount of time. With a touchscreen, the drag is faster, because it doesn't require moving the finger off the screen and then moving it back.

This fact makes gesture-based interfaces more interesting on mobile devices. On the desktop, making a gesture can be slower than clicking on buttons that are close to each other. On a touchscreen, the gesture is often faster.

When applying Fitts' Law on the desktop, it's common to treat objects on the screen edges as being infinitely deep along that axis, because the windowing system clips mouse movements to the edge, meaning that you can overshoot the movement by as much as you like and still hit the target. This is why Mac OS put the menu bar along the top of the screen—it's easier to hit that top edge than to hit something floating in the middle of the screen.

Does this principle apply on touchscreens? Sometimes. The screen itself is a barrier to movement in one dimension, limiting the cost of moving the finger on to the screen. What about the edges? Moving your finger from space to the edge of the screen is about as easy as moving it to the middle of the screen. Dragging can be a different matter, depending on the design of the screen. The N900 has a small raised bevel around the edge of the screen. You can just slide your finger toward the edge and then get tactile feedback that it's time to stop. If you put drop targets around the edge of the screen, you can get some benefit from this design.

It's worth noting that the first system to use this rule efficiently was a PDA from a company named after a fruit. The Newton used the screen edge as a drop target for clippings. When you wanted to copy-and-paste between apps, you dragged something to the edge of the screen and left it there. Later, you would drag it back. This very clever and simple bit of user interface design was somehow forgotten by the company's next attempt at producing handheld computers.

The final thing to remember about touchscreens is that most people have opaque hands. While it's possible to put a mouse pointer over something without obscuring much detail, putting your finger on the touchscreen obscures a lot of the display. Think about positioning when you're placing user interface elements. A good example is the location of onscreen keyboards. They're typically at the bottom of the screen, for a good reason: If the keyboard is at the top, your hand would hide the interface element in which you're entering the text. It's a good idea to keep controls that modify other views near the bottom of the screen.

It's also important to remember the shape of fingers—an area where Apple failed on the iPhone. The iPhone's onscreen keyboard is designed to be used with two thumbs. If you haven't used an iPhone, hold your hand flat against a tabletop and then touch the surface of the table with your thumb. You'll notice that the place where you actually touch the table surface is slightly offset to the right or left (depending on which thumb you use) from the middle of your thumb. Biasing the hit locations for the buttons on the keyboard toward the edge of the screen would have improved typing accuracy, but Apple missed this trick.

  • + Share This
  • 🔖 Save To Your Account

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020