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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_d0e47077_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>
</conbody></concept>