Usability +considerations

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.

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 Power Management section at Forum Nokia.

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.

Interaction +design

Use appropriate and simple interaction logic:

Navigation and controls should be clear and meaningful to prevent mistakes: +strokes along the touch panel should produce a logical outcome.
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.
Meaningful controls are easier to learn and remember.

Touch UI can employ direct or indirect controls, or a combination +of both:

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 UI +components and Touch +support for common UI components.
Indirect controls use some other means to manipulate an object, for +example, shaking, tilting, flipping, waving and so on. For more information, +see Sensor interaction.
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.

+ +

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.

Visual +design

On touch screens, it is important to make a clear distinction +between touchable areas, and non-touchable areas, such as text.

Borders, glow effects, or other indicators can be used to highlight +the interaction.
Note that theme design alone is not sufficient for indicating touch +functionality: where one theme may indicate touch, another may not.