9.2. Sleight of Hand

The layout of Cocoa Touch user interfaces can have a big impact on usability. This is especially true in regards to user interface controls. A control is any interface element that causes the application to do something when a user touches the screen. Standard controls include buttons, sliders, and switches. Table cells can act as controls, as can entire views.

The Multi-Touch interface on the iPhone and iPod Touch requires that applications implement virtual controls. Unlike physical knobs or buttons, virtual controls provide no tactile (or haptic) feedback. A great example of tactile feedback on a hardware control is the raised bumps on the F and J keys of a standard English QWERTY keyboard. These bumps indicate to users that their fingers are in the proper place on the keyboard. On a touchscreen, muscle memory is built with repeated use, but orientation is based purely on the portion of the screen a user is touching.