Before you begin writing a line of code, you should make some critical design decisions. Be as specific as possible about your app’s purpose and features. Choose the kind of data model your app will use. Decide on a user interface style for your app; for example, should it follow a master-detail pattern or that of a utility app? Do you want your app to be universal—that is, an app that runs on iPad, iPhone, and iPod touch? These and other design decisions help you to construct the architecture of your app.
But before you work on that architecture, become familiar with the Cocoa Touch frameworks. After all, your app doesn't exist on its own—it depends on the objects you can create with these frameworks. Get to know the framework objects that implement the basic structure of an app, that serve as the building blocks of your data model, and that compose the unique experience your app presents to users.
An app that is well designed has features that users find appealing, appropriate, and useful. For example, an app might use animation in an effective way. If it allows users to select objects, it might implement copy, cut, and paste. Or it might present text, images, and sounds that are localized to multiple languages.
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