ios - 如何正确设置 NSNotification 并发布？

Question

我想为每个要使用的连接委托(delegate)创建一个单例可达性观察者，
但是我无法正确构建它，这是一些代码片段。

MYReachability.m

static MYReachability *sharedInstance;

+ (MYReachability *)sharedInstance
{
    if (sharedInstance == NULL) {
        sharedInstance = [[MYReachability alloc] init];
    }

    return sharedInstance;
}

- (void)addReachabilityObserver
{
    [[NSNotificationCenter defaultCenter] addObserver: self
                                             selector: @selector(reachabilityChanged:)
                                                 name: kReachabilityChangedNotification
                                               object: nil];

    Reachability *reach = [Reachability reachabilityWithHostname: @"www.apple.com"];
    [reach startNotifier];
}

- (void) reachabilityChanged: (NSNotification *)notification {
    NSLog(@"notification: %@", notification);
    Reachability *reach = [notification object];

    if( [reach isKindOfClass: [Reachability class]]) {
        NetworkStatus status = [reach currentReachabilityStatus];
        NSLog(@"reachability status: %u", status);
        if (status == NotReachable) {
            // Insert your code here
            UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Error"
                                                            message:@"Cannot connect to server..."
                                                           delegate:nil
                                                  cancelButtonTitle:@"OK"
                                                  otherButtonTitles:nil];
            [alert show];
        }
    }
}

在 MYConnectionDelegate.m

- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error
{
    if (error.code) {
        // sending notification to viewController
        [[MYReachability sharedInstance] addReachabilityObserver];
        MYTestClass *myTestClass = [MYTestClass new];
        [myTestClass notificationTrigger];
    }
}

在 MYTestClass.m

- (void)notificationTrigger
{
    // All instances of TestClass will be notified
    [[NSNotificationCenter defaultCenter]
     postNotificationName:kReachabilityChangedNotification
     object:self];
}

瑞克，谢谢，这行得通，但还有另一个问题，
每次调用都会在堆栈中生成一个更多通知...
我在 MYReachability.m 中做了一个 dealloc

- (void)dealloc
{
    [[NSNotificationCenter defaultCenter] removeObserver:self];
}

但之前的通知仍然存在。

Answer 1

您正在调用方法 notificationTrigger但是您的测试类只有方法 notificationTrigger:带有冒号，即一个参数。

更改[myTestClass notificationTrigger];至[myTestClass notificationTrigger:self];它应该可以工作。

如果您只希望通知显示一次，请在显示警报 View 后将自己移除为观察者，如下所示:

- (void) reachabilityChanged: (NSNotification *)notification {
NSLog(@"notification: %@", notification);
Reachability *reach = [notification object];

if( [reach isKindOfClass: [Reachability class]]) {
    NetworkStatus status = [reach currentReachabilityStatus];
    NSLog(@"reachability status: %u", status);
    if (status == NotReachable) {
        // Insert your code here
        UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Error" message:@"Cannot connect to server..." delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil];
        [alert show];
        [[NSNotificationCenter defaultCenter] removeObserver:self];
        }
    }
}