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adding internal behavior to a class without allowing other objects access to it. |
For example, say you want to keep a to-do item’s completionDate updated. If the to-do item gets marked |
as completed, set completionDate to the current date. If it gets marked as uncompleted, set completionDate |
to nil, because it hasn’t been completed yet. Because updating the to-do item’s completionDate is a |
self-contained task, the best practice is to write its own method for it. However, it’s important to make sure |
that other objects can’t call this method—otherwise, another object could set the to-do item’s completionDate |
to anything at any time. For this reason, you make this method private. |
Now, update the implementation of XYZToDoItem to include the private method setCompletionDate that |
gets called inside markAsCompleted: to update the to-do item’s completionDate whenever it gets marked |
as completed or uncompleted. Notice that you’re not adding anything to the interface file, because you don’t |
want other objects to see this method. |
@implementation XYZToDoItem |
- (void)markAsCompleted:(BOOL)isComplete { |
self.completed = isComplete; |
[self setCompletionDate]; |
} |
- (void)setCompletionDate { |
if (self.completed) { |
self.completionDate = [NSDate date]; |
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91 |
Writing a Custom Class |
Methods Define an Object’s Behavior |
} else { |
self.completionDate = nil; |
} |
} |
@end |
At this point, you’ve defined a basic representation of a to-do list item using the XYZToDoItem class. |
XYZToDoItem stores information about itself—name, creation date, completion state—in the form of properties, |
and it defines what it can do—get marked as completed or uncompleted—using a method. This is the extent |
of the features you need to finish implementing your ToDoList app in the next tutorial. However, you can |
always experiment by adding your own properties and methods to the class to integrate new behavior into |
your app. |
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92 |
Tutorial: Add Data |
This tutorial builds on the project you created in the second tutorial (“Tutorial: Storyboards” (page 47)). You’ll |
use what you learned about using design patterns, working with Foundation, and writing a custom class to |
add support for dynamic data to your ToDoList app. |
This tutorial teaches you how to: |
● Work with common Foundation classes |
● |
● |
● |
Create custom data classes |
Implement a delegate and data source protocol |
Pass data between view controllers |
After you complete all the steps in this tutorial, you’ll have an app that looks something like this: |
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93 |
Tutorial: Add Data |
Create a Data Class |
Create a Data Class |
To get started, open your existing project in Xcode. |
At this point, you have an interface and a navigation scheme for your ToDoList app using storyboards. Now, |
it’s time to add data storage and behavior with model objects. |
The goal of your app is to create a list of to-do items, so first you’ll create a custom class, XYZToDoItem, to |
represent an individual to-do item. As you recall, the XYZToDoItem class was discussed in “Writing a Custom |
Class” (page 86). |
To create the XYZToDoItem class |