【IPHONE开发-OBJECTC入门学习】单例对象设计模式

UserController.h

#import <Foundation/Foundation.h>

@interface UserController : NSObject <NSCopying>
{
    int _id;
}

@property (nonatomic,assign) int _id;

- (void) display;

+ (id) defaultUserController:(int) _id;

@end

UserController.m

#import "UserController.h"

static UserController* singleInstance = nil;

@implementation UserController
@synthesize _id;

- (void) display{
    NSLog(@"id = %d,地址 = %p",_id,self);
}

+ (id) defaultUserController:(int) _id {
    @synchronized (self) {
        if (singleInstance == nil) {
            singleInstance = [[[self class] alloc]init];
        }
        singleInstance._id = _id;
    }
    return singleInstance;
}

//下面的方法是为了确保单例对象

+ (id) allocWithZone:(NSZone *)zone {
    if (singleInstance == nil) {
        singleInstance = [super allocWithZone:zone];
    }
    return singleInstance;
}

-(id) retain {
    return singleInstance;
}

-(NSUInteger) retainCount {
    return UINT_MAX;
}

-(oneway void) release {
}

-(id) autorelease{
    return singleInstance;
}

-(id) copyWithZone:(NSZone *)zone {
    return singleInstance;
}

//确保单例对象方法结束

@end

main.m

#import <Foundation/Foundation.h>
#import "UserController.h"

int main(int argc, const char * argv[])
{

    @autoreleasepool {
        
        /*
        
         创建单例对象的基本步骤:
         
         1.声明一个单例对象的静态实例,并初始化为nil
         
         2.创建一个类的类工厂方法,生成一个该类的实例,并且仅在这个类的实例为nil时才生成该类的实例
         
         3.覆盖allocWithZone:方法,确保程序员在直接分配和初始化对象时,不会产生另一个该类的实例对象
         
         4.实现NSCopying协议,覆盖release,autorelease,retain,retainCount方法,以确保单例的状态
         
         5.在多线程环境中,注意使用@synchronized关键字,确保静态实例被正确的创建和初始化
         
         */
        
        UserController* uc1 = [UserController alloc];
        uc1._id = 1;
        [uc1 display];
        
        UserController* uc2 = [[UserController alloc]init];
        uc2._id= 2;
        [uc1 display];
        [uc2 display];
        
        UserController* uc3 = [UserController defaultUserController:3];
        [uc1 display];
        [uc2 display];
        [uc3 display];
        
        UserController* uc4 = [uc1 copy];
        UserController* uc5 = [uc2 retain];
        [uc3 release];
        [uc3 release];
        [uc3 release];
        [uc3 release];
        [uc3 release];
        
        UserController* uc6 = [uc3 autorelease];
        
        [uc4 display];
        [uc5 display];
        [uc6 display];
        
        
        /*
         
         输出结果:
         
         
         2013-06-07 14:44:51.165 单例对象设计模式[2830:403] id = 1,地址 = 0x7fb25ac14530
         2013-06-07 14:44:51.167 单例对象设计模式[2830:403] id = 2,地址 = 0x7fb25ac14530
         2013-06-07 14:44:51.167 单例对象设计模式[2830:403] id = 2,地址 = 0x7fb25ac14530
         2013-06-07 14:44:51.168 单例对象设计模式[2830:403] id = 3,地址 = 0x7fb25ac14530
         2013-06-07 14:44:51.168 单例对象设计模式[2830:403] id = 3,地址 = 0x7fb25ac14530
         2013-06-07 14:44:51.169 单例对象设计模式[2830:403] id = 3,地址 = 0x7fb25ac14530
         2013-06-07 14:44:51.169 单例对象设计模式[2830:403] id = 3,地址 = 0x7fb25ac14530
         2013-06-07 14:44:51.170 单例对象设计模式[2830:403] id = 3,地址 = 0x7fb25ac14530
         2013-06-07 14:44:51.170 单例对象设计模式[2830:403] id = 3,地址 = 0x7fb25ac14530

         
         通过结果能够看到,uc1---uc6这6个对象都指向了同一个内存地址,实现了单例对象设计模式.
         
         */
    }
    return 0;
}