单例模式（singleton）

//  SingletonTools.h
//  单例模式实现
//
//  Created by CloudWalk on 15/9/11.
//  Copyright (c) 2015年 CloudWalk. All rights reserved.
//

#import <Foundation/Foundation.h>

@interface SingletonTools : NSObject
@property(nonatomic,assign) int num;
@property(nonatomic, copy)NSString *s;
// 单例的类，提供一个接入点
+ (instancetype)shareInstance;

@end

//  SingletonTools.m
//  单例模式实现
//
//  Created by CloudWalk on 15/9/11.
//  Copyright (c) 2015年 CloudWalk. All rights reserved.
//

#import "SingletonTools.h"
SingletonTools *instance = nil;

@implementation SingletonTools
// 单利的接入点方法
+ (instancetype)shareInstance
{
    
    if(instance == nil)
    {
        instance = [[SingletonTools alloc] init];
        return instance;
    }
    return instance;
}
@end

//  Person.h
//  单例模式实现
//
//  Created by CloudWalk on 15/9/11.
//  Copyright (c) 2015年 CloudWalk. All rights reserved.
//

#import <Foundation/Foundation.h>

@interface Person : NSObject
- (void)run;
@end

//
//  Person.m
//  单例模式实现
//
//  Created by CloudWalk on 15/9/11.
//  Copyright (c) 2015年 CloudWalk. All rights reserved.
//

#import "Person.h"
#import "SingletonTools.h"
@implementation Person
- (void)run
{
    SingletonTools *st = [SingletonTools shareInstance];
    st.num = 100;
    st.s = @"jajf";
    NSLog(@"%d %@",st.num, st.s);
}
@end

//  main.m
//  单例模式实现
//
//  Created by CloudWalk on 15/9/11.
//  Copyright (c) 2015年 CloudWalk. All rights reserved.
//

#import <Foundation/Foundation.h>
#import "Person.h"
#import "SingletonTools.h"
int main(int argc, const char * argv[]) {
    @autoreleasepool {
        Person *p = [Person new];
        [p run];
    }
    return 0;
}

//  Person.m
//  Created by CloudWalk on 15/9/2.
//  Copyright (c) 2015年 CloudWalk. All rights reserved.
//

#import "Person.h"

// 变量指向单例对象
static Person *singletonInstance = nil;
@implementation Person
+ (id)sharePerson
{
    // 线程锁 
    @synchronized(self)
    {
        // 创建一个单例实例
        if (singletonInstance == nil) {
            singletonInstance = [[[self class] alloc] init];
        }
    }
    return singletonInstance;
}

#pragma mark - 下面的方法为了确保只有一个实例对象
+ (id)allocWithZone:(NSZone *)zone
{
    if (singletonInstance == nil)
    {
        singletonInstance =[super allocWithZone:zone];
    }
    return singletonInstance;
}

// 实现NSCopying协议
- (id)copyWithZone:(NSZone *)zone
{
    return singletonInstance;
}

- (id)retain
{
    return singletonInstance;
}

- (oneway void)release
{
    
}

- (id)autorelease
{
    return singletonInstance;
}

- (NSUInteger)retainCount
{
    return UINT_MAX;
}
@end