Delegates and Data Sources

Before we dive in and start building our application, let's look at what makes pickers more complex than the other controls you've used so far. With the exception of the date picker, you can't use a picker by just grabbing one in the object library, dropping it on your content view, and configuring it. You also need to provide each picker with both a picker delegate and a picker data source.

By this point, you should be comfortable using delegates. We've already used application delegates and action sheet delegates, and the basic idea is the same here. The picker defers several jobs to its delegate. The most important of these is the task of determining what to actually draw for each of the rows in each of its components. The picker asks the delegate for either a string or a view that will be drawn at a given spot on a given component. The picker gets its data from the delegate.