Objective C--享元模式

首先，让我们给出享元模式的定义。

  享元模式(Flyweight)，运用共享技术有效地支持大量细粒度的对象。

  享元模式可以避免大量非常相似类的开销。在程序设计中，有时需要生成大量细粒度的类实例来表示数据。如果能发现这些实例除了几个参数外基本上都是相同的，有时就能够受大幅度地减少需要实例化的类数量。如果能把那些参数移到类实例的外面，在方法调用时将它们传递进来，就可以通过共享大幅度地减少单个实例的数目。

  下面先给出类结构图。

   从图中可以看出，Flyweight执行时所需的状态可能有内部的也可能有外部的，内部状态存储于ConcreteFlyweight对象之中，而外部对象则应该考虑由客户端对象存储或计算，当调用Flyweight对象的操作时，将该状态传递给它。

   那么，一般什么情况下使用享元模式呢？如果一个应用程序使用了大量的对象，而大量的这些对象造成了很大的存储开销时就应该考虑使用；还有就是对象的大多数状态可以作为外部状态，如果删除对象的外部状态，那么可以用相对较少的共享对象取代很多组对象，此时可以考虑使用享元模式。不过，享元模式也是有缺陷的，使用享元模式需要维护一个记录了系统已有的所有享元的列表，而这本身需要耗费资源，另外享元模式使得系统更加复杂。为了使对象可以共享，需要将一些状态外部化，这使得程序的逻辑复杂化。因此，应当在有足够多的对象实例可供共享时才值得使用享元模式。

   好的，下面给出简单的代码实现。

  • Flyweight类接口

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#import <Foundation/Foundation.h>
                 
@interface Flyweight:NSObject
-(void)Operation:(int)extrinsicestate;
@end

  • Flyweight类实现

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#import "Flyweight.h"
                
@implementation Flyweight
-(void)Operation:(int)extrinsicestate{
    return;
}
@end

  • ConcreteFlyweight类接口

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#import "Flyweight.h"
              
@interface ConcreteFlyweight :Flyweight
@end

  • ConcreteFlyweight类实现

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#import "ConcreteFlyweight.h"
            
@implementation ConcreteFlyweight
-(void)Operation:(int)extrinsicestate{
    NSLog(@"具体Flyweight:%d", extrinsicestate);
}
@end

  • UnshareConcreteFlyweight类接口

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#import "Flyweight.h"
          
@interface UnshareConcreteFlyweight:Flyweight
@end

  • UnshareConcreteFlyweight类实现

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#import "UnshareConcreteFlyweight.h"
         
@implementation UnshareConcreteFlyweight
-(void)Operation:(int)extrinsicestate{
    NSLog(@"不共享的具体Flyweight:%d", extrinsicestate);
}
@end

  • FlyweightFactory类接口

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#import <Foundation/Foundation.h>
       
@class Flyweight;
@class ConcreteFlyweight;
@interface FlyweightFactory :NSObject{
    NSMutableDictionary *nd;
}
-(Flyweight*)GetFlyweight:(NSString*)key;
@end

  • FlyweightFactory类实现

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#import "FlyweightFactory.h"
#import "ConcreteFlyweight.h"
     
@implementation FlyweightFactory
-(id)init{
   if (self == [super init]) {
        nd= [NSMutableDictionary dictionary];
        [nd setObject:[[ConcreteFlyweightalloc]init]forKey:@"X"];
        [nd setObject:[[ConcreteFlyweightalloc]init]forKey:@"Y"];
        [nd setObject:[[ConcreteFlyweightalloc]init]forKey:@"Z"];
    }
   return self;
}
-(Flyweight*)GetFlyweight:(NSString*)key{
    return [nd objectForKey:key];
}
@end

  • Main方法调用

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#import <Foundation/Foundation.h>
#import "Flyweight.h"
#import "FlyweightFactory.h"
#import "UnshareConcreteFlyweight.h"
   
int main (int argc,const char * argv[])
{
    @autoreleasepool{
        int extrinsicstate =22;
        FlyweightFactory *f = [[FlyweightFactory alloc]init];
        Flyweight *fx = [f GetFlyweight:@"X"];
        [fx Operation:--extrinsicstate];
        Flyweight *fy = [f GetFlyweight:@"Y"];
        [fy Operation:--extrinsicstate];
        Flyweight *fz = [f GetFlyweight:@"Z"];
        [fz Operation:--extrinsicstate];
        Flyweight *uf = [[UnshareConcreteFlyweight alloc]init];
        [uf Operation:--extrinsicstate];
    }
    return 0;
 

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posted @ 2012-08-16 15:13  Leon Chen2012  阅读(251)  评论(0)    收藏  举报