Objective-C Fundamentals

Building the PocketTasks application
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In viewDidLoad you add a button to add new tasks. The configureCell:atIndex-
Path: method configures a table cell to display the name of the task and to show a
checkmark if the task is done. The addTask method adds a new task and sets its name
to Task 1, Task 2, and so on. Feel free to add a user interface that lets the user enter
a real name for a task. Notice that the person relationship of the task in this method
is set to make the new task belong to the selected person. Also notice the use of
[NSNumber numberWithBool:NO]. Why can’t you just say [task setValue:NO forKey:
@"isDone"]? Because you always have to provide an object for the value, never a primitive
value. That’s why you have to box an integer, double, float, or Boolean value in an
instance of NSNumber.
Finally, the tableView:didSelectRowAtIndexPath: method marks a task as done
by setting the value, saving the context, and calling configureCell:atIndexPath: to
display the checkmark.
To make your new TasksViewController appear when you tap on a person, you
have to go back to PeopleViewController.m once more. Using the code in listing 12.15,
import TasksViewController.h and implement the tableView:didSelectRowAtIndex-
Path: method to create an instance of TasksViewController and push it onto the
navigation controller stack.
Listing 12.15
tableView:didSelectRowAtIndexPath: in PeopleViewController.m
- (void)tableView:(UITableView *)tableView
didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
}
TasksViewController *tasksVC =
[[TasksViewController alloc]
initWithPerson:[resultsController objectAtIndexPath:indexPath]];
[self.navigationController pushViewController:tasksVC animated:YES];
[tasksVC release];
Now build and run the application. You should be able to add tasks and set them to
done by tapping on them (see figure 12.5).
12.4.9 Using model objects
So far you’ve been using NSManagedObject to access your people and tasks. While this
works just fine, it would be much nicer to be able to say [person firstName] (or
person.firstName, the dot notation for properties) instead of [person valueFor-
Key:@"firstName"]. You also need the full name of a person in several places in your
application. Rather than putting the first and last names together every time you need
the full name, you can more efficiently just say [person fullName]. Core Data provides
an easy way to do so using model object classes, which are custom subclasses of
NSManagedObject. You can add your own methods to model object classes and have
nice accessor methods for all the properties and relationships.
To convert PocketTasks to use model object classes, you first let Xcode generate
the appropriate classes for you. Select File > New > New File…, and then select