User Input Methods

Touchscreens enable users to interact with the visual display. There are three types of touchscreen technology:

■ Resistive—Two resistive material layers sit on top of a glass screen.When a finger, stylus, or any object applies pressure, the two layers touch together and the location of the touch can be determined. Resistive touchscreens are cost-effective, but only 75 percent of the light shows through, and until recently, multitouch was not possible.

■ Capacitive—A charged material layer is overlaid on a glass screen.When a finger or any conductive object touches the layer, some charge is drawn off, changing the capacitance, which is measured to determine the location of the touch. Capacitive touchscreens allow as much as 90 percent of the light through, although accuracy can be less than resistive.

■ Surface Acoustic Wave—This uses a more advanced method that sends and receives ultrasonic waves.When a finger or any object touches the screen, the waves are ab-sorbed.The waves are measured to determine the location of the touch. It is the most durable solution, but more suitable for large-scale screens such as automatic bank tellers.

All Android devices use either resistive or capacitive touchscreen technology, and with a few early exceptions, all support multitouch.

In addition, each Android device needs an alternative method to access the screen. This is through one of the following methods:

■ D-pad (directional pad)—An up-down-right-left type ofjoystick

■ Trackball—A rolling ball acting as a pointing device that is similar to a mouse

■ Trackpad—A special rectangular surface acting as a pointing device

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