objective-c - 为什么我的 Singleton 不能保持它的设定值？

Question

我有一个使用单例的应用程序；这是 .h 文件中的代码：

@interface SingletonServicesType : NSObject  {
}
@property (nonatomic, retain) NSNumber *globalServicesType;

+ (id)sharedInstance;
@end

这是 .m 文件中的代码：

//-------------------------------------------
//--  SingletonServicesType
@implementation SingletonServicesType  {  

}

@synthesize globalServicesType;  //  rename

//--  sharedInstance  --
+ (id)sharedInstance  {

static dispatch_once_t dispatchOncePredicate = 0;
__strong static id _sharedObject = nil;
dispatch_once(&dispatchOncePredicate, ^{
    _sharedObject = [[self alloc] init];
});

return _sharedObject;
}

-(id) init {
self = [super init];
if (self) {
    globalServicesType = [[NSNumber alloc] init];
}
return self;
}

@end

这是我在 AppDelegate.m 中设置单例初始值的代码：

    //  set services
SingletonServicesType *sharedInstance = [SingletonServicesType sharedInstance];  //  initialize
if(preferenceData.aServicesType == nil)  {
    sharedInstance.globalServicesType = 0;  //  (0) is the default
    preferenceData.aServicesType = 0;  //  here too...
    [localContext MR_saveNestedContexts];  //  save it...
}
else
    sharedInstance.globalServicesType = preferenceData.aServicesType;  //  0 = default (nails), 1 = custom

NSLog(@"\n\n1-sharedInstance.globalServicesType: %@", [NSNumber numberWithInt: (sharedInstance.globalServicesType)]);  //  shows a value of '0'

当我立即检查另一个类中单例的值时，它是'null'！这是代码：

    SingletonServicesType *sharedInstance = [SingletonServicesType sharedInstance];  //  initialize
NSLog(@"\n\n2-sharedInstance.globalServicesType: %@", sharedInstance.globalServicesType);  //  shows a value of 'null'

我不明白为什么该值保持设置？我错过了什么吗？

Answer 1

这是因为您将零分配给NSNumber*. 您需要分配[NSNumber numberWithInt:0]or @0，否则整数将被解释为地址：

sharedInstance.globalServicesType = @0; // <<== Here