NSNotificationCenter澄清

Question

我是iOS开发中的新手。这是我自己学的。我现在有点搞不懂什么是通知中心。我在网上搜索过，也研究过有关web通知中心的情况。

我之所以发布这个问题，仅仅是为了澄清我对nsnotificationcentre的看法。

我正在建设一个项目，在那里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。现在我把第二视图控制器命名为国家场景，第三视图控制器命名为国家场景，第四视图控制器命名为城市场景。

在国家场景中，我有一个桌子视图，在那里我显示了10个国家的名单。现在，当我点击细胞的时候，它会进入状态场景，在那里我看到了一个桌面视图，在那里我显示了一个10个州的列表，当我点击任何一个单元时，它就进入了城市场景，在那里我看到了一个桌面视图，并显示了一个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。

选择城市就像，

家庭视图控制器->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。

有谁能告诉我怎样才能在nsnotificationcenter做这件事吗？

这是我的家庭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

这是我的国家现场执行文件

#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

这是我的国家现场执行文件

#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

这是我的城市场景实现文件

#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

在您的城市场景中，您必须在通知中传递城市名称作为对象，然后必须在第一个视图控制器(即ViewController )中获取对象。

所以在你的城市场景里，就像这样

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

现在，在您的第一个有文本字段的ViewContrller中，这样做

在viewDidLoad:方法中添加观察者

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

现在实现该方法。

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