NSNotificationCenter澄清

Question

我是全新的iOS开发人员。我正在自己学习。我现在对什么是通知中心有点困惑。我通过网络搜索了关于nsnotification中心的信息。

我发布这个问题只是因为澄清我的想法关于nsnotificationcentre。

我正在建立一个项目，我已经采取了四个视图控制器。第一个视图控制器的名称是默认的。现在我已经将第二个视图控制器命名为乡村场景，将第三个视图控制器命名为州场景，将第四个视图控制器命名为城市场景

在乡村场景中，我有一个表格视图，其中显示了10个国家/地区的列表。现在，当我点击单元格时，它会进入状态场景，在该状态下，我已经看到了一个表格视图，并且在那里显示了10个状态的列表，当我点击任何单元格时，它会转到城市场景，在该场景中，并显示10个城市的列表。

现在在我的第一个视图控制器上，我有两个文本字段。一个是选择国家，一个是选择城市。

我选择了使用代表的国家。现在我想选择城市。

选择城市就会像，

首页视图控制器--->国家视图控制器--->状态视图控制器--->城市视图控制器。然后，我点击该数据的单元格将显示在我的主视图控制器的城市文本框中。

任何人都可以告诉我如何使用nsnotificationcenter来做到这一点？

这是我的家 - 视图 - 控制器实现文件

#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 

这是我的国家场景实现文件

#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 

这是我的国家场景实现文件

#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 

这是我城市场景实施文件

#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

那么在你的城市场景中，你必须通过城市名称作为通知的对象，然后你必须让物体在你的第一个视图控制器即视图控制器

所以，在你的城市场景，不喜欢这

[[NSNotificationCenter defaultCenter]postNotificationName:@"Updated City Name" object:[self.arrCities objectAtIndex:indexPath.row]]; 

现在，在你有文本字段中的第一ViewContrller，做这样的

添加观察者在viewDidLoad:方法

[[NSNotificationCenter defaultCenter]addObserver:self selector:@selector(updateCity:) name:@"Updated City Name" object:nil]; 

现在实行的方法

- (void)updateCity:(NSNotification *)notification { 
    NSString *cityName = notification.object; 
    self.txtCity.text = cityName; 
}