客观C中的单身阶级 [英] singleton class in objective-C

问题描述

我想要一个在代理中初始化的对象，我希望能够在视图控制器的任何地方使用此对象（不依赖于我目前的视图）。我猜这个解决方案是要有一个单身班，到目前为止，我有以下几点：

  @interface LocationManager： NSObject< CLLocationManagerDelegate> {
 NSDate * enter; 
 NSDate * exit; 
 CLLocationManager * manager; 
 
} 
 
 @property（nonatomic，retain）NSDate * enter; 
 @property（nonatomic，retain）NSDate * exit; 
 
  - （BOOL）registerRegionWithLatitude：（double）纬度和长度：（double）longitude; 
 +（LocationManager *）实例; 
 
 @end 
 
 
 #importLocationManager.h
 
 @implementation LocationManager 
 @synthesize enter; 
 @synthesize exit; 
 
 #pragma mark  -  CLLocationManager委托
 static LocationManager * gInstance = NULL; 
 
 
 +（LocationManager *）实例
 {
 @synchronized（self）
 {
 if（gInstance == NULL）
 gInstance = [[self alloc] init]; 
} 
 return（gInstance）; 
} 
 
 @end 
  

这是正确的吗？所以我需要做的只是访问这个只是调用实例？ Inside LocationManager我也想只有一个CLLocationManager，叫做manager ..但是，我在哪里初始化它，所以我只有一个？我可以做以下吗？大多数其他单例示例在类中没有任何变量，所以我感到困惑

  +（LocationManager *）sharedLocationManager 
 {
 @synchronized（self）
 {
 if（lm == NULL）{
 lm = [[self alloc] init]; 
 lm.manager = [[CLLocationManager alloc] init]; 
 lm.manager.delegate = lm; 
} 
} 
 return（lm）; 
} 
  

解决方案

基本上 - br>
只是几个小东西：

static LocationManager * gInstance = NULL;

而不是 NULL ，您应该使用 nil ，这是Objective-C中的惯例。

您还应该覆盖 alloc ，新， copyWithZone：和 mutableCopyWithZone：。从Buck / Yacktman：Cocoa Design Patterns，p。 153：

  +（id）hiddenAlloc 
 {
 return [super alloc]; 
} 
 
 +（id）new 
 {
 return [self alloc]; 
} 
 
 +（id）allocWithZone：（NSZone *）zone 
 {
 return [[self sharedInstance] retain]; 
} 
 
  - （id）copyWithZone：（NSZone *）zone 
 {
 [self retain]; 
返回自我; 
} 
 
  - （id）mutableCopyWithZone :( NSZone *）zone 
 {
 return [self copyWithZone：zone]; 
} 
  

这样，您的单例对象就无法复制。您需要从实例方法调用 hiddenAlloc （顺便说一下，访问Singleton对象的方法通常被称为Objective-C中的 sharedInstance 。

I want to have one object that is initialized in the delegate and I want to be able to use this object anywhere across view controllers (doesn't depend on what view I am currently at). I am guessing the solution to this would be to have a singleton class, so far I have the following:

@interface LocationManager : NSObject <CLLocationManagerDelegate>{
    NSDate *enter;
    NSDate *exit;
    CLLocationManager * manager;

}

@property (nonatomic, retain) NSDate * enter;
@property (nonatomic, retain) NSDate * exit;

- (BOOL)registerRegionWithLatitude:(double)latitude andLongitude:(double)longitude;
+ (LocationManager *)instance;

@end


#import "LocationManager.h"

@implementation LocationManager
@synthesize enter;
@synthesize exit;

#pragma mark - CLLocationManager delegate
static LocationManager *gInstance = NULL;


+ (LocationManager *)instance
{
    @synchronized(self)
    {
        if (gInstance == NULL)
            gInstance = [[self alloc] init];
    }
    return(gInstance);
}

@end

Is this correct? So all I need to do to access this is just to call instance? Inside LocationManager I also want to have only one CLLocationManager, called manager.. however, where do I initialize it so I only have one? Can I do the following? Most other singleton examples doesn't have any variables in the class, so that's where I got confused

+ (LocationManager *)sharedLocationManager
{
    @synchronized(self)
    {
        if (lm == NULL){
            lm = [[self alloc] init];
            lm.manager = [[CLLocationManager alloc] init];
            lm.manager.delegate = lm;
        }
    }
    return(lm);
}

解决方案

Basically -- yes.
Just a couple of small things:
static LocationManager *gInstance = NULL;
instead of NULL, you should use nil, it's a convention in Objective-C.

You should also overwrite alloc, new, copyWithZone:, and mutableCopyWithZone:. From Buck/Yacktman: "Cocoa Design Patterns", p. 153:

+ (id)hiddenAlloc  
{
  return [super alloc];
}

+ (id)new
{
  return [self alloc];
}

+ (id)allocWithZone:(NSZone *)zone
{
  return [[self sharedInstance] retain];
}

- (id)copyWithZone:(NSZone *)zone
{
  [self retain];
  return self;
}

- (id)mutableCopyWithZone:(NSZone *)zone
{
  return [self copyWithZone:zone];
}

This way, your singleton object cannot be copied. You need to call hiddenAlloc from your instance method (by the way, the method to access a Singleton object is often called sharedInstance in Objective-C).

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