Learning the iOS 4 SDK for JavaScript Programmers

Chapter 9. Common JavaScript Tasks in Cocoa Touch

We’ve covered a lot of the basics up to this point. But there are still lots of things you know how to do in JavaScript that could throw you if you intend to implement them in an iOS app. This chapter identifies many of those tasks and shows you how to accomplish them with Cocoa Touch classes and Objective-C techniques. Some tasks are pretty mundane—formatting numbers or calculating dates. But eventually the chapter becomes a bit more fun as you interact more with display elements in the iOS Simulator.

Even if you don’t have a burning need to know how to accomplish one of these tasks in iOS, it will be worth reading through every section. Along the way you’ll learn something new about Xcode, the frameworks, or Objective-C that will be of value in your day-to-day coding. I also don’t expect you to remember everything shown in this chapter, so feel free to come back to it as a reference when the needs arise in the future.

Formatting Numbers for Display

You have seen that working with numbers in the Objective-C environment requires careful observation of data typing. Number values and objects (such as the NSNumber) concern themselves with the values they represent, rather than how the numbers are to be formatted for display as currency, percentages, or nicely aligned columns with necessary zero padding. Just as can happen in JavaScript, blindly converting a number to a string for display can cause unexpected results, such as too many or ...