Codefile [UtilityApplication.zip] available for download at Wrox.com

How It Works

Much of the work needed in a Utility Application is already done for you. But it is always good to understand how things work under the hood so that you can extend it for your own use.

As you have seen, the project contains two main views controlled by two view controllers: MainViewController and FlipsideViewController.

First, examine the content of the FlipsideViewController.h file:

@protocol FlipsideViewControllerDelegate;

@interface FlipsideViewController : UIViewController {
    id <FlipsideViewControllerDelegate> delegate;
}
@property (nonatomic, assign) id <FlipsideViewControllerDelegate> delegate;

- (IBAction)done;

@end

@protocol FlipsideViewControllerDelegate
- (void)flipsideViewControllerDidFinish:(FlipsideViewController *)controller;
@end

Notice that in this controller, the code defines a protocol called the FlipsideViewControllerDelegate, which contains a single method called flipsideViewControllerDidFinish:. Using this protocol, the FlipsideViewController then exposes a property called delegate of type FlipsideViewControllerDelegate. The actual implementation of the flipsideViewControllerDidFinish: method is not defined in this controller; instead, it must be defined by whatever calls it (in this case, it is the MainViewController). Its use is to signal to the calling view controller that it is done and control should return to the calling view controller.

In the FlipsideViewController.m file, the implementation for the done: method is defined in the header file:

- (IBAction)done {
    [self.delegate flipsideViewControllerDidFinish:self];
}

Basically this method calls the flipsideViewControllerDidFinish: method that you have defined (but implemented elsewhere) in the FlipsideViewControllerDelegate protocol.

Now, double-click the FlipsideView.xib file to open it in Interface Builder. Observe the following:

Now you can examine the MainViewController.h file:

#import "FlipsideViewController.h"

@interface MainViewController : UIViewController <FlipsideViewController
Delegate> {
}

- (IBAction)showInfo;

@end

Observe that the MainViewController implements the FlipsideViewControllerDelegate protocol. In other words, it must implement the method that is defined in the protocol (which in this case is the flipsideViewControllerDidFinish: method).

In the MainViewController.m file, a method named flipsideViewControllerDidFinish: is defined. Its use is to close the FlipsideView when it is done:

- (void)flipsideViewControllerDidFinish:(FlipsideViewController *)
controller {
    [self dismissModalViewControllerAnimated:YES];
}

The MainViewController.m file also contains an action called showInfo(). This action is invoked when the user presses the Info button. The showInfo() action loads the FlipsideView modally:

- (IBAction)showInfo {

    FlipsideViewController *controller = [[FlipsideViewController alloc]
                                       initWithNibName:@"FlipsideView"
                                       bundle:nil];
    controller.delegate = self;

    controller.modalTransitionStyle = UIModalTransitionStyleFlipHorizontal;
    [self presentModalViewController:controller animated:YES];

    [controller release];
}

If you double-click the MainView.xib to edit it in Interface Builder, you can right-click the Info button to confirm that its Touch Up Inside event is connected to the showInfo() action (see Figure 9-5).

Figure 9.5. Figure 9-5

So there you have it — a Utility Application that works magically without the need for you to write any code!

How It Works

This example illustrates the steps you need to take to add more views to a Utility Application. You first create the XIB file of the additional view as well as its corresponding UIViewController class. Within this controller, you define a protocol:

//---defines the protocol---
@protocol AddCountryViewControllerDelegate
- (void)addCountryViewControllerDidFinish:(AddCountryViewController *)controller;
@end

You then expose a property of this protocol type:

@interface AddCountryViewController : UIViewController {
    //---delegate---
    id <AddCountryViewControllerDelegate> delegate;
}

//---exposes the delegate as a property---
@property (nonatomic, assign) id <AddCountryViewControllerDelegate> delegate;

The view that will call this new view needs to implement the method defined in this protocol, which is as follows:

- (void)addCountryViewControllerDidFinish:
(AddCountryViewController *)controller;

When the user presses the Done button in this view, you invoke the done: method:

//---invokes the method defined in the protocol---
- (IBAction)done {
    [self.delegate addCountryViewControllerDidFinish:self];
}

In the FlipsideViewController.m file, you need to implement the protocol defined in the additional view, which is AddCountryViewControllerDelegate:

//---implements the AddCountryViewControllerDelegate protocol---
@interface FlipsideViewController : UIViewController
                                    <AddCountryViewControllerDelegate> {

Specifically, you need to implement the addCountryViewControllerDidFinish: method, which dismisses the view controller:

//---defines the addCountryViewControllerDidFinish: method---
- (void)addCountryViewControllerDidFinish:
(AddCountryViewController *)controller {
    [self dismissModalViewControllerAnimated:YES];
}

Finally, you define the add: method, which shows the additional view using the vertical transition:

//---defines the add: action---
- (IBAction)add {
    AddCountryViewController *controller = [[AddCountryViewController alloc]
                                           initWithNibName:@"AddCountryView"
                                           bundle:nil];
    controller.delegate = self;

    //---use the vertical transition---
    controller.modalTransitionStyle = UIModalTransitionStyleCoverVertical;
    [self presentModalViewController:controller animated:YES];

    [controller release];
}