iOS设计模式 (四)享元模式

• 享元模式（英语：Flyweight Pattern)。使用共享物件，减少同一类对象的大量创建，尽可能减少内存使用量以及分享资讯给尽可能多的相似物件,运用共享技术有效地支持大量细粒度的对象。

• 享元模式UML

  
  4.png

• 实现享元模式需要两个关键组件，
  1.可攻享享元对象
  2.享元池
  工厂是这一角色的理想候选。它可以通过一个工厂方法，根据父类型返回各种类型的具体享元对象，其主要的目的就是使用池中的享元对象，并适当地从中返回享元对象。

• 享元模式的使用场景
  @：应用程序使用很多对象。
  @：在内存中保存对象会影响内存性能。
  @：对象的多数特有状态可以放到外部而轻量化。
  @：移除了外在状态后，可以用较少的共享对象替代原来的那组对象。
  @：应用程序不依赖于对象标识，因为共享对象不能提供唯一的标识。

享元模式的实例应用

• User类

#import <Foundation/Foundation.h>

@interface User : NSObject

@property (nonatomic, copy)NSString *useName;

@end
#import "User.h"

@implementation User

@end

• FlySiteProtocol 协议

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

@protocol FlySiteProtocol <NSObject>

- (void)use:(User *)user;

@end

• ConcreteFlySite 类

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

@interface ConcreteFlySite : NSObject <FlySiteProtocol>

@property (nonatomic, copy) NSString *webName;

@end
#import "ConcreteFlySite.h"


@implementation ConcreteFlySite

- (void)use:(User *)user
{
    NSLog(@"网站分类:%@ 用户名字:%@", self.webName, user.useName);
}

@end

• FlyWeightFactory 工厂类

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

@interface FlyWeightFactory : NSObject

@property (nonatomic, strong) NSDictionary *flyweights; //共享对象

- (id <FlySiteProtocol>)flyWeightCategory:(NSString *) webKey;

- (NSInteger )getWebSiteCount;
@end

#import "FlyWeightFactory.h"
#import "ConcreteFlySite.h"

@implementation FlyWeightFactory

- (instancetype)init
{
    self = [super init];
    if (self) {
        _flyweights= [NSDictionary dictionary];
    }
    return self;
}

- (id <FlySiteProtocol>)flyWeightCategory:(NSString *)webKey
{
    __block id <FlySiteProtocol> webFlySet = nil;
    
    [self.flyweights enumerateKeysAndObjectsUsingBlock:^(id  _Nonnull key, id  _Nonnull obj, BOOL * _Nonnull stop) {
        if (webKey == key) {
            webFlySet = obj;
            * stop = YES;
        }
    }];
    
    if (webFlySet == nil) {
        ConcreteFlySite *concrete = [[ConcreteFlySite alloc] init];
        concrete.webName = webKey;
        webFlySet = concrete;
        
        NSMutableDictionary *mutableDict = [NSMutableDictionary dictionaryWithDictionary:self.flyweights];
        [mutableDict setObject:webFlySet forKey:webKey];
        self.flyweights = [NSDictionary dictionaryWithDictionary:mutableDict];
    }
    
    return webFlySet;
    
}

- (NSInteger)getWebSiteCount {
    return self.flyweights.count;
}

@end

• ViewController 类

#import "ViewController.h"
#import "FlyWeightFactory.h"
#import "ConcreteFlySite.h"
#import "User.h"
#import "FlySiteProtocol.h"

typedef id <FlySiteProtocol> WebsiteType;

@interface ViewController ()

@end

@implementation ViewController


- (NSArray *)testArray
{
    NSMutableArray *array = [NSMutableArray array];
    
    for (NSInteger i =  0; i < 5000; i ++) {
        if (i %2 == 0) {
            [array addObject:[NSString stringWithFormat:@"订单%ld",(long)i]];
        }
        else {
            [array addObject:[NSString stringWithFormat:@"订单%ld",(long)i]];
        }
    }
    
    return array;
}

- (void)viewDidLoad {
    [super viewDidLoad];
    
    // 通过工厂方法返回各种具体享元对象,维护池中的享元对象
    FlyWeightFactory *factory = [[FlyWeightFactory alloc] init];
    
    
    for (NSInteger i = 0; i < [self testArray].count; i++ ) {
        WebsiteType type  = [factory flyWeightCategory:[self testArray][i]];
        User *user = [[User alloc] init];
        user.useName = [NSString stringWithFormat:@"用户%ld",i];
        [type use:user];
    }
    
//     WebsiteType type1 =  [factory flyWeightCategory:@"首页"];
//
//    NSLog(@"factroy=====:%ld",[factory getWebSiteCount]);
//
////    //  返回具体的享元对象
//
//    User *user1 = [[User alloc] init];
//    user1.useName = @"张三";
//    // 享元对象都具有use方法
//    [type1 use:user1];
//
//    WebsiteType type2 = [factory flyWeightCategory:@"商店"];
//    User *user2 = [[User alloc] init];
//    user2.useName = @"李四";
//    [type2 use:user2];
//
//     NSLog(@"factroy111=====:%ld",[factory getWebSiteCount]);
}
@end

• demo地址：https://github.com/defuliu/FlyweightPattern.git
• 参考案例： http://www.mamicode.com/info-detail-1037340.html
• 对比下xcode的运行内存