iPhone Application Development : User Input and Output

Although application logic is always the most important part of an application, the way the interface works plays a big part in how well it will be received. For Apple and the iPhone, providing a fun, smooth, and beautiful user experience has been key to its success; it’s up to you to bring this experience into your own development. The iPhone SDK’s interface options give you the tools to express your application’s functionality in fun and unique ways.

This hour introduces two very visual interface features: sliders for input and image views for output.

Sliders

The first new interface component that we’ll be using this hour is a slider (UISlider). Sliders are a convenient touch control that is used to visually set a point within a range of values. Huh? What?

Suppose that you want your user to be able to speed something up or slow it down. Asking users to input timing values is unreasonable. Instead, you can present a slider, as seen in Figure 1, where they can touch and drag an indicator back and forth on a line. Behind the scenes, a value property is being set that your application can access and use to set the speed. No need for users to understand the behind-the-scene details or do anything more than drag with their fingers.

Figure 1. Use a slider to collect a value from a range of numbers without requiring users to type.

Sliders, like buttons, can react to events or can be read passively like a text field. If you want the user’s changes to a slider to immediately have an effect on your application, you must have it trigger an action.

Image Views

Image views (UIImageView) do precisely what you’d think: They display images! They can be added to your application views and used to present information to the user. An instance of UIImageView can even be used to create a simple frame-based animation with controls for starting, stopping, and even setting the speed at which the animation is shown.

With iOS 4, your image views can even take advantage of the high-resolution display of the iPhone 4 (and any other upcoming iOS high-resolution devices). Even better, you need no special coding! Instead of checking for a specific device, you can just add multiple images to your project, and the image view will load the right one at the right time.