iphone - NSNotification 中的文本字段未更新

Question

我正在做一个关于 NSNotification 的简单教程，但在正确执行它时遇到了一些问题。当我单击第一个 View 上的按钮时，第二个 View 中的文本字段没有得到更新。当我通过在 receiveNotification 中放置一个 NSLog 进行调试时，没有响应。不确定为什么未调用 receiveNotification。

代码如下所示:

ViewController.h

#import <UIKit/UIKit.h>

@interface ViewController : UIViewController{

}
-(IBAction)one:(id)sender;
-(IBAction)two:(id)sender;
-(IBAction)secondview:(id)sender;
@end

ViewController.m

#import "ViewController.h"
#import "SecondViewController.h"

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}
-(IBAction)one:(id)sender{
    [[NSNotificationCenter defaultCenter] postNotificationName:@"Test1" object:self];
    NSLog(@"Hello");
}
-(IBAction)two:(id)sender{
    [[NSNotificationCenter defaultCenter] postNotificationName:@"Test2" object:self];
     NSLog(@"Hello");
}
-(IBAction)secondview:(id)sender{
    SecondViewController *secondview = [[SecondViewController alloc] initWithNibName:@"SecondViewController" bundle:nil];
    [self presentViewController:secondview animated:YES completion:nil];
}

@end

SecondViewController.h

#import <UIKit/UIKit.h>

@interface SecondViewController : UIViewController{
    IBOutlet UITextField *counterOneText;
    IBOutlet UITextField *counterTwoText;
    int counterOne;
    int counterTwo;
}

-(IBAction)back:(id)sender;
@end

SecondViewController.m

#import "SecondViewController.h"

@interface SecondViewController ()

@end

@implementation SecondViewController

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {

        counterOne = 0;
        counterTwo = 0;

        [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(receiveNotification) name:@"Test1" object:nil];
        [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(receiveNotification) name:@"Test2" object:nil];
    }
    return self;
}

-(void)receiveNotification:(NSNotification *)notification{
    if([[notification name] isEqualToString:@"Test1"])  {
        counterOne++;
        counterOneText.text = [NSString stringWithFormat:@"%d",counterOne];
        NSLog(@"%@",counterOneText.text);
        NSLog(@"Hello");
    }else
    {
        counterTwo++;
        counterTwoText.text = [NSString stringWithFormat:@"%d",counterTwo];
    }
}

- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view from its nib.
}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}
-(IBAction)back:(id)sender{
    [self dismissViewControllerAnimated:YES completion:nil];
}

@end

需要一些指导......

Answer 1

receiveNotification 未被调用，因为您的 SecondViewController 从未实例化。当对象不存在时无法调用它。如果您按下 secondView，back，然后单击 one 或 two，则会触发 receiveNotification。

编辑:我复制并粘贴了你的代码来测试它，我得到了你想要它做的大部分事情。您仍然需要先按 secondview，然后按 back。

在 ViewController.m 中

@interface ViewController (){
    SecondViewController *secondview;
}

@end

@implementation ViewController

-(id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil{
    self = [super initWithNibName: nibNameOrNil bundle:nibBundleOrNil];
    if(self){
        secondview = [[SecondViewController alloc] initWithNibName:@"SecondViewController" bundle:nil];
    }
    return self;
}

- (void)viewDidLoad
{
    [super viewDidLoad];

    // Do any additional setup after loading the view, typically from a nib.
}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}
-(IBAction)one:(id)sender{
    [[NSNotificationCenter defaultCenter] postNotificationName:@"Test1" object:self];
}
-(IBAction)two:(id)sender{
    [[NSNotificationCenter defaultCenter] postNotificationName:@"Test2" object:self];
}
-(IBAction)secondview:(id)sender{
    [self presentViewController:secondview animated:YES completion:nil];
}

在SecondViewController.h中

@interface SecondViewController : UIViewController{
    int counterOne;
    int counterTwo;
}

@property (nonatomic,retain)UITextField *counterOneText;

@property (nonatomic,retain)UITextField *counterTwoText;


-(IBAction)back:(id)sender;

@end

在SecondViewController.m中

@interfaceSecondViewController()

@结束

@implementation SecondViewController
@synthesize counterOneText, counterTwoText;

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {

        counterOne = 0;
        counterTwo = 0;

        self.counterOneText = [[UITextField alloc]initWithFrame:CGRectMake(100, 50, 150, 30)];
        self.counterOneText.borderStyle = UITextBorderStyleRoundedRect;
        self.counterOneText.text = [NSString stringWithFormat:@"%@", [NSNumber numberWithInt:counterOne]];

        self.counterTwoText = [[UITextField alloc]initWithFrame:CGRectMake(100, 100, 150, 30)];
        self.counterTwoText.borderStyle = UITextBorderStyleRoundedRect;
        self.counterTwoText.text = [NSString stringWithFormat:@"%@", [NSNumber numberWithInt:counterTwo]];

        //self.counterOneText.text = [NSString stringWithFormat:@"%d",counterOne];
        //self.counterTwoText.text = [NSString stringWithFormat:@"%d",counterTwo];


        [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(receiveNotification:) name:@"Test1" object:nil];
        [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(receiveNotification:) name:@"Test2" object:nil];
    }
    return self;
}

-(void)receiveNotification:(NSNotification *)notification{
    if([[notification name] isEqualToString:@"Test1"])  {
        counterOne++;
        NSLog(@"counterOne: %d", counterOne);
        counterOneText.text = [NSString stringWithFormat:@"%@", [NSNumber numberWithInt:counterOne]];

        NSLog(@"counterOneText.text: %@",counterOneText.text);
        NSLog(@"Test1");
    }else
    {
        counterTwo++;
        NSLog(@"counterTwo: %d", counterTwo);
        counterTwoText.text = [NSString stringWithFormat:@"%@",[NSNumber numberWithInt:counterTwo]];

        NSLog(@"counterTwoText.text: %@",counterTwoText.text);
        NSLog(@"Test2");


    }

}

- (void)viewDidLoad
{
    [self.view addSubview:self.counterOneText];
    [self.view addSubview:self.counterTwoText];
    [super viewDidLoad];
    // Do any additional setup after loading the view from its nib.
}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}
-(IBAction)back:(id)sender{
    [self dismissViewControllerAnimated:YES completion:nil];
}