我是 iOS 开发的新手。我正在自己学习这个。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 的看法。

我正在构建一个项目，其中我使用了四个 View Controller 。第一个 View Controller 的名称是默认的。现在我将第二个 View Controller 命名为乡村场景，第三个 View Controller 命名为州场景，第四个 View Controller 命名为城市场景。

在国家场景中，我有一个表格 View ，其中显示了 10 个国家/地区的列表。现在，当我点击单元格时，它会转到我拍摄表格 View 的州场景，并在那里显示 10 个州的列表，当我点击任何单元格时，它会转到我拍摄表格 View 的城市场景并显示 10 个城市的列表。

现在在我的第一个 View Controller 上，我有两个文本字段。一种用于选择国家，一种用于选择城市。

我选择了使用代表的国家。现在我要选择城市。

选择城市会像这样，

主页 View Controller ---> 国家 View Controller ---> 州 View Controller ---> 城市 View Controller 。然后我点击该数据的单元格将显示在我的主视图 Controller 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 ()
{
BOOL fromCountry;
}
@kết thúc

@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];
}
@kết thúc

这是我的乡村场景实现文件

#import "CountryViewController.h"
#import "StateViewController.h"
#import "ViewController.h"

@interface CountryViewController ()

@property (nonatomic) NSString *lastSelectedCountryName;





@kết thúc

@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];
}
khác
    [self performSegueWithIdentifier: @"stateScene" sender: self];
}

@kết thúc

这是我的状态场景实现文件

#import "StateViewController.h"

@interface StateViewController ()

@kết thúc

@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.
}


@kết thúc

这是我的城市场景实现文件

#import "CityViewController.h"

@interface CityViewController ()

@kết thúc

@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.
}

@kết thúc

1 Câu trả lời

在你的城市场景中，你必须将城市名称作为通知中的对象传递，然后你必须在你的第一个 View Controller 中获取对象，即 ViewController

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]];

现在在你的第一个有文本字段的 ViewController 中，这样做

Trong của bạnviewDidLoad: 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;
}

关于ios - NSNotificationCenter 说明，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/29143938/