如何從NSNotification對象獲取數據？

Question

我試圖發送位置更新與新位置作爲通知對象。當我這樣做時，當我嘗試訪問通知中的數據時，會收到「EXC_BAD_ACCESS」錯誤。如果我執行「po location」，我會看到數據，但是我不清楚爲什麼我無法獲取它。設置觀察者時，我也嘗試將對象參數分配給成員變量，但是不會調用locationUpdate。

這裏是我的代碼（注意，ARC已啓用）：

// LocationController.h

@protocol LocationDelegateProtocol 
@required 
    - (void)locationUpdate:(CLLocation *)location; 
@end 

@interface LocationController : NSObject <CLLocationManagerDelegate> { 
    CLLocationManager *locationManager; 
    id delegate; 
} 

@property(nonatomic, retain) CLLocationManager *locationManager; 
@property(nonatomic, strong) id delegate; 

- (void)locationManager:(CLLocationManager *)manager didUpdateToLocation:(CLLocation *)newLocation fromLocation:(CLLocation *)oldLocation; 

+ (LocationController *)sharedInstance; // this class is a singleton 

@end 

// LocationController.m

- (void)locationManager:(CLLocationManager *)manager didUpdateToLocation:(CLLocation *)newLocation fromLocation:(CLLocation *)oldLocation { 
    [Notification locationChanged:newLocation]; 
} 

// Notification.h

@interface Notification : NSObject 
    + (void)locationChanged:(CLLocation *)newLocation; 
@end 

extern NSString *const kLocationChanged; 

// Notification.m

NSString *const kLocationChanged = @"NewLocation"; 

[[NSNotificationCenter defaultCenter] postNotificationName:kLocationChanged object:newLocation]; 

// ViewController.h

@interface ViewController : UIViewController <UITableViewDelegate, UITableViewDataSource, LocationDelegateProtocol> { 
    ... 
} 
... 
- (void)locationUpdate:(CLLocation *)location; 

@end 

// ViewController.m

- (void)setupNotifications { 
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(locationUpdate:) name:kLocationChanged object:nil]; 
    // I've tried setting object to a member var "CLLocation *objectFromNotification", but then locationUpdate() is never called. 
} 

- (void)locationUpdate:(NSNotification *)notification {  
    CLLocation *location = (CLLocation *) [notification object]; 
    // program receives signal "EXC_BAD_ACCESS" when executing NSLog below. I can see data inside location when I execute "po location". 
    NSLog(@"latitude = %@, longitude = %@",location.coordinate.latitude, location.coordinate.longitude); 

Answer 1

改變你的NSLog格式說明從％@到％F 。您正試圖將float值作爲對象訪問！

Answer 2

NSNotifications有一個與他們的字典叫userInfo，你可以把你要與通知發送信息。

我要解決你的代碼有點倒退......所以裸陪我。您確實沒有使用NSNotification類，因爲它通常（或打算）被使用。我們不得不做很多事情。 NSNotification文章的object值是發佈NSNotification的對象，而不是您想要傳遞的對象。

將CLLocation對象添加到字典中，並將其作爲userInfo字典傳入。這個自定義通知類也沒有任何理由。所以，你可以擺脫​​和Notification.m

- (void)locationManager:(CLLocationManager *)manager didUpdateToLocation:(CLLocation *)newLocation fromLocation:(CLLocation *)oldLocation { 
    NSString *const kLocationChanged = @"NewLocation"; 
    NSDictionary *locationDict = [NSDictionary dictionaryWithObject:newLocation forKey:@"Location"]; 
    [[NSNotificationCenter defaultCenter] postNotificationName:kLocationChanged object:nil userInfo:locationDict]; 
} 

所以，現在我們正在發佈該通知的位置信息。接下來，當你收到通知時處理它。

- (void)locationUpdate:(NSNotification *)notification {  
    CLLocation *location = [[notification userInfo] valueForKey:@"Location"]; 

    NSLog(@"latitude = %f, longitude = %f",location.coordinate.latitude, location.coordinate.longitude); 
} 

此外，您的視圖控制器頭更改爲以下：

@interface ViewController : UIViewController <UITableViewDelegate, UITableViewDataSource, LocationDelegateProtocol> { 
    ... 
} 
... 
- (void)locationUpdate:(NSNotification *)notif; 

@end