NSNotificationCenter 澄清

Question

我是 iOS 开发的新手。我正在自学这个。我现在对什么是通知中心有点困惑。我通过网络搜索并研究了nsnotification中心。

我发布这个问题只是为了澄清我对 nsnotificationcentre 的想法。

我正在构建一个项目，其中我采用了四个视图控制器。第一个视图控制器的名称是默认的。现在我将第二个视图控制器命名为乡村场景，第三个视图控制器命名为州场景，第四个命名为城市场景。

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，它会进入我已获取表格视图的状态场景，并在那里显示 10 个状态的列表，当我点击任何单元格时，它会进入我已获取表格视图的城市场景并显示 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。一种是选择国家，一种是选择城市。

我使用代表选择了国家。现在我想选择城市。

选择城市会像这样，

主页视图控制器 ---> 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字段中。

谁能告诉我如何使用 nsnotificationcenter 做到这一点？

这是我的 Home View Controller 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 Country Scene 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

这是我的状态场景实现文件

#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，您必须在通知中将城市名称作为对象传递，然后您必须在您的第一个视图控制器（即 ViewController）中获取对象

所以在你的城市场景中，这样做

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

现在在你的第一个 ViewContrller 中，你有文本字段，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];

现在实现方法

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