How to use NSNotification in iOS?

1. Adding an observer 

[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(loadDataWithNotification:) name:@"Test" object:nil];
2. Adding the observe method:

- (void)loadDataWithNotification: (NSNotification *) notification
{

if ([notification.name isEqualToString:@"Test"]) {
NSLog(@"Notification received");
[self retrieveData];
}
}
3. Posting notification on the other ViewController.

[[NSNotificationCenter defaultCenter] postNotificationName:@"Test" object:nil];


Notification will be sent back to the MainViewController when the user click on the add Button, in order to notify the MainViewController to reload its data.
MainViewController



DetailViewController



Main code:

TableViewController.h

//
// TableViewController.h
// CoreDataTutorial
//
// Created by Jason on 28/05/12.
// Copyright (c) 2012 __MyCompanyName__. All rights reserved.
//

#import <UIKit/UIKit.h>
@interface TableViewController : UITableViewController

@property (strong, nonatomic) NSManagedObjectContext *context;
@end

TableViewController.m

//
// TableViewController.m
// CoreDataTutorial
//
// Created by Jason on 28/05/12.
// Copyright (c) 2012 __MyCompanyName__. All rights reserved.
//

#import "TableViewController.h"
#import "DetailViewController.h"
#import "People.h"

@interface TableViewController ()
@property (strong, nonatomic) NSArray *peopleArray;
@end

@implementation TableViewController
@synthesize peopleArray=_peopleArray;
@synthesize context=_context;

//retrieve data
- (void)retrieveData
{
NSFetchRequest *request=[[NSFetchRequest alloc] init];
NSEntityDescription *entity=[NSEntityDescription entityForName:@"People" inManagedObjectContext:self.context];

NSSortDescriptor *sortDescriptor=[[NSSortDescriptor alloc] initWithKey:@"name" ascending:YES];

request.entity=entity;
request.sortDescriptors=[NSArray arrayWithObject:sortDescriptor];
request.fetchBatchSize=20;
NSError *error;
self.peopleArray=[self.context executeFetchRequest:request error:&error];
[self.tableView reloadData];
}

- (void)loadDataWithNotification: (NSNotification *) notification
{

if ([notification.name isEqualToString:@"Test"]) {
NSLog(@"Notification received");
[self retrieveData];
}
}

- (id)initWithStyle:(UITableViewStyle)style
{
self = [super initWithStyle:style];
if (self) {
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(loadDataWithNotification:) name:@"Test" object:nil];
}
return self;
}

- (void)viewDidLoad
{
[super viewDidLoad];
[self retrieveData];

// Uncomment the following line to preserve selection between presentations.
// self.clearsSelectionOnViewWillAppear = NO;

// Uncomment the following line to display an Edit button in the navigation bar for this view controller.
self.navigationItem.rightBarButtonItem =[[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemAdd target:self action:@selector(add)];
}

- (void)add
{
DetailViewController *detailView=[[DetailViewController alloc] init];
[self presentModalViewController:detailView animated:YES];
}

- (void)viewDidUnload
{
[super viewDidUnload];
// Release any retained subviews of the main view.
// e.g. self.myOutlet = nil;
}

- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
return (interfaceOrientation == UIInterfaceOrientationPortrait);
}

#pragma mark - Table view data source

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
return 1;
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
return self.peopleArray.count;
}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *CellIdentifier = @"Cell";
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];

// Configure the cell...
if (!cell) {
cell=[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleSubtitle reuseIdentifier:CellIdentifier];
}

People *people=(People *)[self.peopleArray objectAtIndex:indexPath.row];
cell.textLabel.text=people.name;
cell.detailTextLabel.text=[NSString stringWithFormat:@"%@",people.number];

return cell;
}

/*
// Override to support conditional editing of the table view.
- (BOOL)tableView:(UITableView *)tableView canEditRowAtIndexPath:(NSIndexPath *)indexPath
{
// Return NO if you do not want the specified item to be editable.
return YES;
}
*/

/*
// Override to support editing the table view.
- (void)tableView:(UITableView *)tableView commitEditingStyle:(UITableViewCellEditingStyle)editingStyle forRowAtIndexPath:(NSIndexPath *)indexPath
{
if (editingStyle == UITableViewCellEditingStyleDelete) {
// Delete the row from the data source
[tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade];
}
else if (editingStyle == UITableViewCellEditingStyleInsert) {
// Create a new instance of the appropriate class, insert it into the array, and add a new row to the table view
}
}
*/

/*
// Override to support rearranging the table view.
- (void)tableView:(UITableView *)tableView moveRowAtIndexPath:(NSIndexPath *)fromIndexPath toIndexPath:(NSIndexPath *)toIndexPath
{
}
*/

/*
// Override to support conditional rearranging of the table view.
- (BOOL)tableView:(UITableView *)tableView canMoveRowAtIndexPath:(NSIndexPath *)indexPath
{
// Return NO if you do not want the item to be re-orderable.
return YES;
}
*/

#pragma mark - Table view delegate

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
// Navigation logic may go here. Create and push another view controller.
/*
<#DetailViewController#> *detailViewController = [[<#DetailViewController#> alloc] initWithNibName:@"<#Nib name#>" bundle:nil];
// ...
// Pass the selected object to the new view controller.
[self.navigationController pushViewController:detailViewController animated:YES];
*/
}

@end


DetailViewController.h

//
// DetailViewController.h
// CoreDataTutorial
//
// Created by Jason on 28/05/12.
// Copyright (c) 2012 __MyCompanyName__. All rights reserved.
//

#import <UIKit/UIKit.h>
#import "AppDelegate.h"

@interface DetailViewController : UIViewController
{
IBOutlet UITextField *nameField;
IBOutlet UITextField *numberField;
}

@end


DetailViewController.m

//
// DetailViewController.m
// CoreDataTutorial
//
// Created by Jason on 28/05/12.
// Copyright (c) 2012 __MyCompanyName__. All rights reserved.
//

#import "DetailViewController.h"
#import "People.h"

@interface DetailViewController ()

@property (nonatomic, strong) AppDelegate *app;

@end

@implementation DetailViewController
@synthesize app=_app;

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
if (self) {
UINavigationBar *navigationBar=[[UINavigationBar alloc] initWithFrame:CGRectMake(0, 0, 320, 44)];
UINavigationItem *
a10a
navigationItem=[[UINavigationItem alloc] initWithTitle:@"Add Detail"];
[navigationBar pushNavigationItem:navigationItem animated:YES];

UIBarButtonItem *addButton=[[UIBarButtonItem alloc] initWithTitle:@"Add" style:UIBarButtonItemStyleBordered target:self action:@selector(add)];
UIBarButtonItem *cancelButton=[[UIBarButtonItem alloc] initWithTitle:@"Cancel" style:UIBarButtonItemStyleBordered target:self action:@selector(cancel)];

navigationItem.leftBarButtonItem=cancelButton;
navigationItem.rightBarButtonItem=addButton;

//adding navigationBar
[self.view addSubview:navigationBar];
}
return self;
}

- (void)viewDidLoad
{
[super viewDidLoad];
self.app=[[UIApplication sharedApplication] delegate];
}

- (void)add
{
NSManagedObjectContext *context=self.app.managedObjectContext;
People *people=[NSEntityDescription insertNewObjectForEntityForName:@"People" inManagedObjectContext:context];

people.name=nameField.text;
people.number=[NSNumber numberWithInt:[numberField.text intValue]];

NSError *error;
if (![context save:&error ]) {
UIAlertView *alert=[[UIAlertView alloc] initWithTitle:@"Error" message:@"Can not save people"delegate:self cancelButtonTitle:@"OK" otherButtonTitles:nil];
[alert show];
}else {
UIAlertView *alert=[[UIAlertView alloc] initWithTitle:@"saved" message:@"The record has saved" delegate:self cancelButtonTitle:@"OK" otherButtonTitles:nil];
[alert show];
}

[[NSNotificationCenter defaultCenter] postNotificationName:@"Test" object:nil];
[self dismissModalViewControllerAnimated:YES];

}

- (void)retrieveData
{
//retrieving data
NSManagedObjectContext *context=self.app.managedObjectContext;

NSFetchRequest *request=[[NSFetchRequest alloc] init];
NSEntityDescription *entityDescription=[[NSEntityDescription alloc] init];
request.entity=entityDescription;
NSError *error;
NSArray *peopleArray=[context executeFetchRequest:request error:&error];

for(People *people in peopleArray){
NSLog(@"name=%@,number=%@",people.name, people.number);
}
}

- (void)cancel
{
[self dismissModalViewControllerAnimated:YES];
}

- (void)viewDidUnload
{
[super viewDidUnload];
// Release any retained subviews of the main view.
// e.g. self.myOutlet = nil;
}

- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
return (interfaceOrientation == UIInterfaceOrientationPortrait);
}

@end