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.

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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.