观察员不工作

Question

我试图让观察者在我的笔记本电脑自动更改其wifi连接时通知我。

我有一个“NetworkProperties”类，用于存储我的连接属性：

@interface NetworkProperties : NSObject
{
@public
    CWInterface *wfi;
@private
    CWWiFiClient *wfc;

    NSString *SSID;
    NSString *BSSID;
    NSString *phyMode;
    NSString *hwAddr;
    NSString *securityType;
}
@end

和一个“GUIHandle”类，我尝试处理我的GUI。我还有以下功能来启用/禁用扫描：

@interface GUIHandle : NSObject
{
    NetworkProperties *NP;
}

-(IBAction)startScan:(id)sender;
-(IBAction)stopScan:(id)sender;

@end

-(IBAction)startScan:(id)sender
{
    done = 0;

    NP = [[NetworkProperties alloc] init];
    [NP scanNetworkProperties];

    [NP->wfi addObserver:self forKeyPath:@"bssid" options:NSKeyValueObservingOptionNew  context:nil];
}

-(IBAction)stopScan:(id)sender
{
    [NP->wfi removeObserver:self forKeyPath:@"bssid"];
}


- (void) observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context {

    NSLog(@"We are here!\n");
    if ([keyPath isEqual:@"bssid"]) {
        NSLog(@"Value changed!\n");
    }
}

但是，如果我的连接的“bssid”发生变化，我不会收到任何通知。我做错了什么？