單例值仍然爲零

Question

我正在嘗試使用單例概念來保留GPS信息，但我沒有看到問題在哪裏，我的變量顯示僅爲零。

Singleton.h：

@interface Singleton : NSObject 

@property (readwrite) NSString *propertyA; 
@property (readwrite) NSString *propertyB; 
@property (readwrite) NSString *propertyC; 

+ (Singleton *)sharedInstance; 

@end 

Singleton.m：

#import "Singleton.h" 

@interface Singleton() 
{ 
    NSString *variableA; 
    NSString *variableB; 
    NSString *variableC; 
} 
@end 

@implementation Singleton 

static Singleton *sharedInstance = nil; 

+ (Singleton *)sharedInstance 
{ 
    @synchronized(self) { 
     if (sharedInstance == nil) { 
      sharedInstance = [[Singleton alloc] init]; 
     } 
    } 
    return sharedInstance; 
} 

+ (id)allocWithZone:(NSZone *)zone { 
    @synchronized(self) { 
     if (sharedInstance == nil) { 
      sharedInstance = [super allocWithZone:zone]; 
      return sharedInstance; 
     } 
    } 
    return nil; 
} 

- (id)init 
{ 
    self = [super init]; 
    if (self) 
    { 
     variableA = nil; 
     variableB = nil; 
     variableC = nil; 
    } 
    return self; 
} 

@end 

在OverlayViewController.m：

#import "Singleton.h" 

- (void)locationManager:(CLLocationManager *)manager didUpdateToLocation:(CLLocation *)newLocation fromLocation:(CLLocation *)oldLocation 
{ 
     NSLog(@"didUpdateToLocation: %@", newLocation); 
     CLLocation *currentLocation = newLocation; 

     if (currentLocation != nil) { 
      _longitudeLabel.text = [NSString stringWithFormat:@"%.8f", currentLocation.coordinate.longitude]; 
      _latitudeLabel.text = [NSString stringWithFormat:@"%.8f", currentLocation.coordinate.latitude]; 
     } 

     // Setting properties 
     NSString *variableA = _latitudeLabel.text; 
     [[Singleton sharedInstance] setPropertyA:variableA];  
} 

於是又記起值位進一步下跌...

- (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary *)info 
{ 
    NSString *variableA = [[Singleton sharedInstance] propertyA];  
    NSLog(@"Latitude = %.8f", variableA); 
} 

個

感謝紅塔

Answer 1

我的第一個猜測是，你沒有任何@synthesize任何地方，所以有沒有setter/getter方法

如果不工作，那麼你應該將你的變量聲明您的.h文件中，我不明白你爲什麼會對他們在您的m反正

我指的是這樣的：

@interface Singleton() 
{ 
    NSString *variableA; 
    NSString *variableB; 
    NSString *variableC; 
} 
@end 

編輯： 種兩次與單身人士打交道時的良好做法：

1）聲明你static ClassName *singleton你的方法裏面，這樣在你的類中的其他方法不必直接訪問它，需要有[[self class] sharedInstance];

2要求的話）使用dispatch_once線程安全

+ (FooBar *)sharedInstance { 
    static dispatch_once_t pred; 
    static FooBar *_sharedInstance = nil; 

    dispatch_once(&pred, ^{ 
     _sharedInstance = [[[self class] alloc] init]; 
    }); 

    return _sharedInstance; 
} 

Answer 2

@property (readwrite) NSString *propertyA;
@property (readwrite) NSString *propertyB;
@property (readwrite) NSString *propertyC;

我想上面的變量沒有setter和getters，意思是你會被要求對它們進行合成。

這就是爲什麼下面的代碼沒有設置PropertyA的值。

[[Singleton sharedInstance] setPropertyA:variableA];