Objective-C 真正意义的单实例()

//
//  Singleton.h
//  singleton
//
//  Created by leondun on 11-4-20.
//  Copyright 2011 leondun. All rights reserved.
//
 
#import <Foundation/Foundation.h>
 
 
@interface Singleton : NSObject {
 
}
 
+(Singleton *)getInstance;
 
@end

#import "Singleton.h"
 
static Singleton * instance = nil;
 
@interface Singleton(privateMethods)
 
-(void)realRelease;
 
@end
 
 
@implementation Singleton
 
//获取单例
+(Singleton *)getInstance
{
    @synchronized(self) {
        if (instance == nil) {
            [[self alloc] init];
            }
    }
    return instance;
}
 
//唯一一次alloc单例，之后均返回nil
+ (id)allocWithZone:(NSZone *)zone
{
    @synchronized(self) {
        if (instance == nil) {
            instance = [super allocWithZone:zone];
            return instance;
        }
    }
    return nil;
}
 
//copy返回单例本身
- (id)copyWithZone:(NSZone *)zone
{
    return self;
}
 
//retain返回单例本身
- (id)retain
{
    return self;
}
 
//引用计数总是为1
- (unsigned)retainCount
{
    return 1;
}
 
//release不做任何处理
- (void)release
{
   
}
 
//autorelease返回单例本身
- (id)autorelease
{
    return self;
}
 
//真release私有接口
-(void)realRelease
{
      [super release];
}
 
//
-(void)dealloc
{
      //⋯⋯
      printf("举例:在此处做一些单例结束时的收尾处理/n"); 
      [super dealloc];
}
 
@end
 
//程序结束时析构静态c++类对象garbo，
//在Garbo类的析构函数中释放instance
struct Garbo
{
      ~Garbo(){[instance realRelease];}
};
static Garbo garbo;