NSNotificationCenter Clarification - ios

Question

I am totally new in iOS developing. I am learning this on my own. I am now a little bit confused about what is notification centre. I have searched through web and studied about nsnotification centre.
I am posting this question just because to clarify my idea about nsnotificationcentre.
I am building a project where I have taken four view controllers. The name of the first view controller is default as it is. Now I have named the second view controller as country scene, the third view controller as state scene and the fourth one as city scene.
In country scene I have a table view where I am showing a list of 10 countries. Now when I am tapping on cells it goes to the state scene where I have taken a table view and there I am showing a list of 10 states and when I am tapping on any cells it goes to city scene where I have taken a table view and showing a list of 10 cities.
Now on my first view controller, I have two text fields. One is for choosing countries and one is for choosing cities.
I have chosen the countries using delegates. Now I want to choose cities.
Choosing cities will go like,
Home view controller ---> Country view controller ---> State view controller ---> City view controller. Then the cell where I tap that data will show in the city textfield of my home view controller.
Can any one please tell me how can I do this with nsnotificationcenter?
This is my Home View Controller implementation file
#import "ViewController.h"
#import "CountryViewController.h"
#interface ViewController ()<countryDelegate>
{
BOOL fromCountry;
}
#end
#implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
self.txtCity.delegate = self;
self.txtCountry.delegate = self;
self.txtCountry.text = self.strname;
[[NSNotificationCenter defaultCenter]addObserver:self selector:#selector(updateCityName:) name:#"Updated City Name" object:nil];
}
-(void)updateCity:(NSString *)city
{
self.txtCity.text = city;
}
-(void) dealloc{
[[NSNotificationCenter defaultCenter] removeObserver:self name:#"Updated City Name" object:nil];
}
- (BOOL)textFieldShouldBeginEditing:(UITextField *)textField{
if (textField.tag == 1) {
fromCountry=YES;
}
else{
[self performSegueWithIdentifier:#"countryScene" sender:self];
}
return YES;
}
- (void) prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender{
[_txtCountry resignFirstResponder];
CountryViewController *detailObject = (CountryViewController *) segue.destinationViewController;
detailObject.delegate=self;
detailObject.isFromCountry = fromCountry;
}
-(void)updateCountry:(NSString *)country
{
_txtCountry.text=country;
}
- (void)didReceiveMemoryWarning {
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
- (IBAction)countryButtonClicked:(id)sender {
fromCountry=YES;
[self performSegueWithIdentifier:#"countryScene" sender:self];
}
#end
This is my Country Scene implementation file
#import "CountryViewController.h"
#import "StateViewController.h"
#import "ViewController.h"
#interface CountryViewController ()
#property (nonatomic) NSString *lastSelectedCountryName;
#end
#implementation CountryViewController
- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view.
self.arrCountries = #[#"India", #"Bangladesh", #"Australia", #"New Zealand", #"South Africa", #"West Indies", #"Sri Lanka", #"England", #"Argentina", #"Brazil"];
}
- (void)didReceiveMemoryWarning {
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:#"countryCell"];
UILabel *lblCountry = (UILabel*)[cell.contentView viewWithTag:3];
lblCountry.text = [self.arrCountries objectAtIndex:indexPath.row];
return cell;
}
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section{
return [self.arrCountries count];
}
- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
if (_isFromCountry) {
if ([self.delegate respondsToSelector:#selector(updateCountry:)])
{
[self.delegate updateCountry:[_arrCountries objectAtIndex:indexPath.row]];
}
[self.navigationController popViewControllerAnimated:YES];
}
else
[self performSegueWithIdentifier: #"stateScene" sender: self];
}
#end
This is my State Scene implementation file
#import "StateViewController.h"
#interface StateViewController ()
#end
#implementation StateViewController
- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view.
self.arrStates = #[#"West Bengal", #"Uttar Pradesh", #"Madhya Pradesh", #"Jharkhand", #"Bihar", #"Tamilnadu", #"Myanmar", #"Arunachal Pradesh", #"Assam", #"Goa"];
}
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:#"stateCell"];
UILabel *lblStates = (UILabel*)[cell.contentView viewWithTag:4];
lblStates.text = [self.arrStates objectAtIndex:indexPath.row];
return cell;
}
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section{
return [self.arrStates count];
}
- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
[self performSegueWithIdentifier: #"cityScene" sender: self];
}
- (void)didReceiveMemoryWarning {
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
#end
This is my City Scene implementation file
#import "CityViewController.h"
#interface CityViewController ()
#end
#implementation CityViewController
- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view.
self.arrCities = #[#"Kolkata", #"Bangalore", #"Chennai", #"Mumbai", #"Hyderabad", #"Mangalore", #"New York", #"London", #"Rio de Janeiro", #"Buenos Aires"];
}
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:#"cityCell"];
UILabel *lblCities = (UILabel*)[cell.contentView viewWithTag:5];
lblCities.text = [self.arrCities objectAtIndex:indexPath.row];
return cell;
}
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section{
return [self.arrCities count];
}
- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
[[NSNotificationCenter defaultCenter]postNotificationName:#"Updated City Name" object:nil];
}
- (void)didReceiveMemoryWarning {
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
#end

Answer 1

Well in your city scene you have to pass the city name as the object in the notification and then you have to get object in your first view controller i.e. ViewController
So in your city scene, do like this
[[NSNotificationCenter defaultCenter]postNotificationName:#"Updated City Name" object:[self.arrCities objectAtIndex:indexPath.row]];
Now in your first ViewContrller where you have text fields, do like this
Add the observer in your viewDidLoad: method
[[NSNotificationCenter defaultCenter]addObserver:self selector:#selector(updateCity:) name:#"Updated City Name" object:nil];
Now implement the method
- (void)updateCity:(NSNotification *)notification {
NSString *cityName = notification.object;
self.txtCity.text = cityName;
}