Whatever it does, your app almost certainly does a lot of stuff that other apps do. This is the whole reason why frameworks exist, and Cocoa's frameworks supply you with a huge number of classes and structs that save you writing all that code again. A framework is, in the end, nothing more than some lines of finished code, possibly accompanied by resources such as images or localized strings, which is made available to your project.
There are likely to be times when the functionality you need to write is not available from any Cocoa framework, or is not in a form that suits your requirements. And on many of these occasions, you'll find that someone else has faced the same situation, and has made their solution available to other developers, often for free.
So this chapter deals with the reasons for and against using other people's code, and covers some of the ways that we can integrate that code into our own projects.
We will be covering the following...