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<concept id="GUID-056165A7-E8A1-4868-8051-9EC58C5A3342" xml:lang="en"><title>Usability

considerations</title><prolog><metadata><keywords/></metadata></prolog><conbody>

<section id="GUID-E4B60228-49E7-415D-AFF1-9E9B622D2197"> <p>All touch and

gestural interfaces have to appear competent and safe. The interface needs

to look as though it is not going to misuse users' personal data or break

down. Optimizing system performance is critical here. Low screen refresh rate

and latent images do not give the impression of a trustworthy touch UI. The

use of touch screen and sensors may also increase battery consumption of mobile

devices.</p><note><p>Touch screens consume most power during touch operations,

and reducing unnecessary user interaction can help increase power efficiency.

Specifically with resistive touch screens, avoiding excessively long touch

and drag user actions is recommended. The continuous touch event flow keeps

the CPU busy. The screen lock turns off the touch completely. To learn more

about both optimizing system performance and battery life in Symbian applications,

see the <xref href="http://www.forum.nokia.com/main/resources/user_experience/power_management/" scope="external">Power Management</xref> section at Forum Nokia.</p></note><p>The

best products predict the needs of their users and then fulfill those needs

in unexpectedly pleasing ways. Adaptive targets are one way to do this.  Controls

that match the users actions well are another way devices can be clever.</p> <p><b>Interaction

design</b></p><p>Use appropriate and simple interaction logic:</p><ul>

<li><p>Navigation and controls should be clear and meaningful to prevent mistakes:

strokes along the touch panel should produce a logical outcome. </p></li>

<li><p>The coolest interaction in the world is empty unless it has clear meaning

for the person performing it. When using indirect controls, the UI response

should relate to the action the user is performing. </p></li>

<li><p>Meaningful controls are easier to learn and remember. </p></li>

</ul> <p>Touch UI can employ direct or indirect controls, or a combination

of both:</p><ul>

<li><p>Direct controls allow users to simply tap the item they want to manipulate

right on the screen itself, move it, make it bigger, scroll it, and so on.

For more information, see <xref href="GUID-CCE6DC36-625C-487C-9AD8-F1BF8E36080A.dita">UI

components</xref> and <xref href="GUID-BB8B3A11-0BBC-4759-A7F4-A28C9E70573F.dita">Touch

support for common UI components</xref>. </p></li>

<li><p>Indirect controls use some other means to manipulate an object, for

example, shaking, tilting, flipping, waving and so on. For more information,

see <xref href="GUID-AE979B97-5610-42F3-99A7-5A3D66D3C2E6.dita">Sensor interaction</xref>.</p></li>

<li><p>While the Symbian style provides for the use of scroll bars, it is

common to reverse the page scrolling orientation in applications such as browser.

In absence of scroll bars, users will flick or drag the page upwards rather

than pull a scroller down to move the page up, that is, to scroll down. In

this case, scroll bars are used as navigation indicators.</p></li>

</ul><fig id="GUID-604A80CE-CB23-45A9-BC29-A01395CD6A2F">

<image href="GUID-EE5937B6-9103-4711-B13B-06A62D56AF79_d0e72052_href.png" scale="60" placement="inline"/>

</fig><p>Direct taps and strokes are far easier for the user to understand

and pick up than abstract, indirect ones. A single view should always employ

only a few indirect strokes, so that the controls do not confuse the user. </p><p><b>Visual

design</b></p><p>On touch screens, it is important to make a clear distinction

between touchable areas, and non-touchable areas, such as text. </p><ul>

<li><p>Borders, glow effects, or other indicators can be used to highlight

the interaction. </p></li>

<li><p>Note that theme design alone is not sufficient for indicating touch

functionality: where one theme may indicate touch, another may not.</p></li>

</ul><p>See also:</p><ul>

<li><p><xref href="GUID-5486EFD3-4660-4C19-A007-286DE48F6EEF.dita">Scale and positioning

of controls</xref></p></li>

<li><p><xref href="GUID-3CA039D8-A74D-4C9E-B4F5-6E153C7F65A1.dita">Finger vs. stylus</xref></p></li>

<li><p><xref href="GUID-7BFEEDF7-3DB8-42FF-9D7A-F98E536F7686.dita">Sensor interaction</xref></p></li>

</ul> </section>