View controllers are used for managing a view. The class used for controlling the views is called UIViewController and is provided by UIKit. To manage the view, we'll create a UIViewController subclass:

We're going to define a delegate protocol in the header file of the new View Controller class AddNameController.h. A delegate protocol must declare several methods, and the classes conforming to a delegate protocol must implement the methods declared in it. The classes that conform to a delegate protocol are known as delegates. The delegates are the classes responsible for implementing the methods of the confirming protocol. Let's go ahead and define the delegate protocol.

A protocol is defined using the @protocol compiler directive combined with an @end directive. Between the two directives, we declare the protocol methods. The following shows the code that we will write in the View controller class header file, AddNameController.h:

// AddNameController.h
// demotable
#import <UIKit/UIKit.h>
@protocol AddNameControllerDelegate;
@interface AddNameController : UIViewController {
id <AddNameControllerDelegate> delegate;
IBOutlet UIBarButtonItem *cancelbutton;
IBOutlet UIBarButtonItem *savebutton;
IBOutlet UITextField *newname;
}
@property(nonatomic, retain) id <AddNameControllerDelegate>
delegate;
@property(nonatomic, retain) IBOutlet UIBarButtonItem *cancelbutton;
@property(nonatomic, retain) IBOutlet UIBarButtonItem *savebutton;
@property(nonatomic, retain) UITextField *newname;
-(IBAction) cancel:(id) sender;
-(IBAction) save:(id)sender;
@end
@protocol AddNameControllerDelegate
-(void) addnameController:(AddNameController *)controller
selectedsave:(BOOL) save name:(NSString *) newname;
@end

We can see that an AddNameControllerDelegate protocol is defined, called delegate. The method declared in the AddNameControllerDelegate is addnameController. A class conforming to this protocol must implement this method.

Besides defining a delegate protocol, we also define three outlets: cancelbutton, savebutton, and newname. The two outlets, cancelbutton and savebutton, will be connected to the two Bar Button Items that we will soon drag-and-drop onto the View. The outlets will be titled Save and Cancel respectively. The newname outlet will be connected to the Text Field control of the View in which the user enters the new name to be added to the Table View.

The header file includes two action methods, cancel and save, which will be connected to the Cancel and Save Bar Button Items.

The next step is to add two Bar Button Item controls to the AddNameController's View and connecting them with the outlets and action methods defined in the preceding header file.

The steps for adding Bar Button Item controls to the view and for connecting them with the respective outlet and action methods are given as follows:

To connect the cancelbutton and savebutton outlets defined in the header file with the Bar Button Item controls in the Documents window, follow these steps:

To connect the save and cancel action methods with the Bar Button Item controls, follow these steps:

The following screenshot shows the process for cancelbutton. When we select the Bar Button Item control in the View window, the cancel method code we will be writing in the implementation file—will be executed.

Repeat this procedure to connect save to the other Bar Button Item control. These Bar Button Item controls will be useless if they don't result in some action when clicked. So, let's make ground for these Bar Button Item controls to initiate action.

We need to write code in the AddNameController.m implementation file to invoke the delegate methods when Bar Button Item controls are pressed. The following code fragment also includes code that places the Bar Button items on the left and right side of the navigation bar. The following is the code that we write in the implementation file:

// AddNameController.m
// demotable
#import "AddNameController.h"
@implementation AddNameController
@synthesize savebutton;
@synthesize cancelbutton;
@synthesize delegate;
@synthesize newname;
-(IBAction) cancel:(id) sender
{
[delegate addnameController: self selectedsave:NO
name:newname.text];
}
-(IBAction) save:(id)sender{
[delegate addnameController: self selectedsave:YES
name:newname.text];
}
// Implement viewDidLoad to do additional setup after loading the view, typically from a nib.
- (void)viewDidLoad {
[super viewDidLoad];
self.title=@"New Name";
self.navigationItem.rightBarButtonItem=savebutton;
self.navigationItem.leftBarButtonItem=cancelbutton;
}
- (void)didReceiveMemoryWarning {
// Releases the view if it doesn't have a superview.
[super didReceiveMemoryWarning];
// Release any cached data, images, etc. that aren't in use.
}
Table Viewdelegate methods, invoking in AddNameController.m implementation file- (void)viewDidUnload {
[super viewDidUnload];
// Release any retained subviews of the main view.
// e.g. self.myOutlet = nil;
}
- (void)dealloc {
[savebutton release];
[cancelbutton release];
[newname release];
[super dealloc];
}
@end

The sequence of events is as follows:

First we synthesize the IBOutlets savebutton, cancelbutton, delegate, and newname, so we can generate their accessor and mutator methods.

In the cancel action method, invoke the addnameController method and set the value of selectedsave to NO.

So far, we've defined a View that prompts the user to enter the name to be added to the Table View. The next task is to write code for invoking the AddNameController view from the main page of the application, that is, from the RootViewController view. Also we need to write code for displaying the entered name in the Table View. Let's go ahead and do that now.

We need to invoke this AddNameController View from the Root View Controller and implement the AddNameController delegate protocol methods. The RootView Controller class will be the class conforming to the AddNameControllerDelegate delegate protocol defined in the AddNameController.h header. Thus, the following shows the code that we will write in the RootViewController class:

// RootViewController.h
// demotable
#import <UIKit/UIKit.h>
#import <CoreData/CoreData.h>
#import "AddNameController.h"
@interface RootViewController : UITableViewController <NSFetchedResultsControllerDelegate, AddNameControllerDelegate> {
NSMutableArray *nameslist;
IBOutlet UIBarButtonItem *addbutton;
@private
NSFetchedResultsController *fetchedResultsController_;
NSManagedObjectContext *managedObjectContext_;
}
@property (nonatomic, retain) NSManagedObjectContext *managedObjectContext;
@property (nonatomic, retain) NSFetchedResultsController *fetchedResultsController;
@property(nonatomic, retain) NSMutableArray *nameslist;
@property(nonatomic, retain) IBOutlet UIBarButtonItem *addbutton;
-(IBAction)addname:(id)sender;
@end

To make the RootViewController class adopt the delegate protocol so that it implements the methods declared in the protocol we first add the protocol's name. We can see AddNameControllerDelegate in angle brackets, which declares that the RootViewController class conforms to the AddNameControllerDelegate protocol and guarantees that the class implements the methods declared in the protocol. We also add an addbutton IBOutlet, called UIBarButtonItem, which will be connected to the Bar Button Item control. When this control is selected, the addname action method is invoked. In turn, this action method invokes the View of the AddNameController class that prompts the user to enter the name to be added to the Table View. The next step is to add a Bar Button Item controller to the view of the RootViewController class and connect it with the outlet and action method defined in the preceding header file. So, let's do it.

Let's open the RootViewController.xib file in Interface Builder and drag a Bar Button Item control from the Windows, Views & Bars category of the Library window and drop it into the Documents window, as shown in the following screenshot. With the help of the Attributes Inspector, set the Title property of the Bar Button Item control to Add.

Then follow this series of steps:

Now we need to write the code in the Root View Controller implementation file to invoke the AddNameController View and implement the addnameController method declared by AddNameControllerDelegate. The following shows the code that we will write in the RootViewController.m file:

// RootViewController.m
// demotable
#import "RootViewController.h"
@implementation RootViewController
@synthesize fetchedResultsController=fetchedResultsController_, managedObjectContext=managedObjectContext_;
@synthesize nameslist;
@synthesize addbutton;
- (void)viewDidLoad {
[super viewDidLoad];
nameslist=[[NSMutableArray alloc] initWithObjects: @"Brian",
@"David",@"Charles", @"Mike", nil];
[self setTitle:@"Names List"];
self.navigationItem.rightBarButtonItem=addbutton;
}
-(IBAction)addname:(id)sender
{
AddNameController *addnameController=[[AddNameController alloc]
initWithNibName:@"AddNameController" bundle:nil];
addnameController.delegate=self;
UINavigationController *navController=[[UINavigationController
alloc] initWithRootViewController:addnameController];
[self.navigationController
presentModalViewController:navController animated:YES];
[addnameController release];
[navController release];
}
-(void) addnameController:(AddNameController *)controller
selectedsave:(BOOL) save name:(NSString *)newnme{
if(save)
{
[nameslist addObject:newnme];
[self.tableView reloadData];
}
[self dismissModalViewControllerAnimated:YES];
}
#pragma mark Table view methods
- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView {
return 1;
}
// Customize the number of rows in the table view.
- (NSInteger)tableView:(UITableView *)tableView
numberOfRowsInSection:(NSInteger)section {
return [nameslist count];
}
// Customize the appearance of table view cells.
- (UITableViewCell *)tableView:(UITableView *)tableView
cellForRowAtIndexPath:(NSIndexPath *)indexPath {
static NSString *CellIdentifier = @"Cell";
UITableViewCell *cell = [tableView
dequeueReusableCellWithIdentifier:CellIdentifier];
if (cell == nil) {
cell = [[[UITableViewCell alloc]
initWithStyle:UITableViewCellStyleDefault
reuseIdentifier:CellIdentifier] autorelease];
}
cell.textLabel.text=[nameslist objectAtIndex:indexPath.row];
return cell;
}
- (void)dealloc {
[nameslist release];
[addbutton release];
[super dealloc];
}
@end

Here's what's happening in the code:

When the Add button is selected, the AddNameController View appears, as shown in the preceding image (b), which prompts the user to enter a new name. When the user enters a name and selects the Save button (shown in the preceding image (c)), the new name will appear in the Table View, as shown in preceding image (d).