【IPHONE开发-OBJECTC入门学习】单例对象设计模式

桃扇骨 2022-01-28 04:11 166阅读 0赞

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;
    }