Objective-C Fundamentals

Summary
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The core of the logic occurs in the alertView:clickedButtonAtIndex: method. This
method is invoked when the user taps the right-hand button on the navigation bar
and selects a desired filter condition. The method first creates an NSPredicate
instance detailing which properties should still be displayed in the UITableView.
This predicate then filters the array of all rental properties (allProperties) using
the predicate to come up with a new array (filteredProperties) consisting of the
subset of rental properties that meet the specified conditions. The UITableView is
then requested to reload using this second array to display the filtered set of rental
properties to the user.
11.5 Summary
KVC- and NSPredicate-based logic is a powerful way to query, filter, analyze, and
access data from an in-memory object-based data model. And this is just the tip of the
iceberg of KVC’s true power.
The real power of KVC begins to shine when you realize the level of abstraction it can
provide. When we discussed key-path operators such as @min, @max, and @distinct-
UnionOfObjects, you may have noticed that you expressed, in a simple string format,
what operation was required, then left it up to the framework to determine how to
iterate over the data model and any memory management issues or temporary data
structures required to produce the results.
In chapter 12 you discover that all the concepts discussed in this chapter are transferrable
for use with Core Data–based object models. Although the programming
model is equivalent and familiar, behind the scenes, the implementation couldn’t be
more different. In the case of Core Data, KVC converts key paths and NSPredicatebased
filter expressions into Structured Query Language (SQL) queries that are executed
at the database level.
As a programmer, you for the most part don’t care. You worry about the creation of
the required filter conditions and leave it up to the framework to determine how best
to implement the required logic.
Next up in chapter 12, you’ll learn all about Core Data and how it can help you in
the creation of robust iOS applications.