ios 取消注册观察者

Question

我正在阅读 Apple 文档并看到:

Before an object that is observing notifications is deallocated, it must tell the notification center to stop sending it notifications. Otherwise, the next notification gets sent to a nonexistent object and the program crashes.

我尝试让应用程序崩溃，以更好地了解它的实际工作原理。

但是，即使我没有将此代码放入 SecondViewController dealloc 中，发送通知后它仍然不会崩溃。显然我正在添加观察者并从 SecondViewController 返回并在 viewController 中推送通知。那么，如果这个程序不会崩溃，为什么我们需要删除观察者呢？

[[NSNotificationCenter defaultCenter] removeObserver:self];

其余代码是:

// View Controller :

@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)go:(id)sender {
    SecondViewController *secondViewController = [[SecondViewController alloc] initWithNibName:@"SecondViewController" bundle:nil];
    [self presentViewController:secondViewController animated:NO completion:^{}];
    [secondViewController release], secondViewController = nil; }

- (IBAction)push:(id)sender {
    // All instances of TestClass will be notified
    [[NSNotificationCenter defaultCenter] postNotificationName:@"TestNotification" object:self]; }

//第二个 View Controller :

@implementation SecondViewController

- (void)dealloc {
    [super dealloc]; }

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil {
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
        // Custom initialization
        [[NSNotificationCenter defaultCenter] addObserver:self
                                                 selector:@selector(receiveTestNotification:)
                                                     name:@"TestNotification"
                                                   object:nil];

    }
    return self; }

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

- (void) receiveTestNotification:(NSNotification *) notification {
    // [notification name] should always be @"TestNotification"
    // unless you use this method for observation of other notifications
    // as well.
    NSLog (@"Successfully received the test notification!"); }

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated. }

- (IBAction)back:(id)sender {
    NSLog(@"");
    [self dismissViewControllerAnimated:NO completion:^{}]; }

Answer 1

@Reno Jones 是对的。 像这样删除观察者 - [[NSNotificationCenter defaultCenter] removeObserver:self name:@"TestNotification"object:nil];

在他的答案中还要添加的一件事是，您应该删除 - (void)dealloc {} 方法中的观察者 - 这是释放 self 时调用的方法。

编辑:

我查看了代码，发现您没有使用 arc。还有一个问题，为什么你不在你的应用程序中使用 ARC？你有充分的理由通过引用计数来给自己施加压力吗？我不明白这一点？

其次，您可以在 viewDidLoad 方法中移动 addObserver 并查看它是否会导致您的应用程序崩溃。