Touch Accuracy
An instance of UITouch exposes its location as a
two-dimensional CGPoint value. Each CGPoint represents an (x, y) pair of
float values. Clearly, even the tiniest fingertip is much larger than a
single point on the screen. The iPhone does a great job of training users
to expect and accept the approximate fidelity that results from
translating a physical touch to a single point in the coordinate space of
a view. Still, developers with an appreciation for user experience should
pay attention to the perception of accuracy. If a user feels that input
results in a loss of precision, frustration is a likely outcome.
The main considerations for touch accuracy are:
The size of touchable objects
The shape of touchable objects
The placement of touchable objects in relation to one another
The overlapping of touchable objects
Size
The size of touchable objects is an interesting problem. One of the more curious facets
of a portable touch interface is that the main input device (a finger)
also obfuscates the feedback mechanism (the screen). Touching a control,
such as a button, should provide users with visual feedback to provide a
confirmation that their intentions have been communicated to the device.
So how does Apple address this issue in UIKit? They
attack the issue from many angles.
First, many controls are quite large. By displaying buttons that span approximately 80% of the width of the screen, Apple guarantees that users can see portions of the button in both its highlighted and ...
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