Objective C 迭代器模式

迭代器模式(Iterator)，提供一種方法順序訪問一個聚合對象中各個元素，而又不暴露該對象的內部表示。

   那麼一般在什麼時候纔會用迭代器模式呢？當你需要訪問一個聚集對象，而且不管這些對象是什麼都需要遍歷的時候，你就應該考慮用迭代器模式。另外，當你需要對聚集有多種方式遍歷時，也可以考慮用迭代器模式。

   說了這麼多，下面給大家展示一下類關係圖。

   上圖中Client的右邊是迭代器，左邊是具體迭代的類型，在迭代器內部對具體需要迭代的類型進行了引用，還算不難理解吧，呵呵。其實，看起來是爲了對具體類型進行解耦。好啦，下面給出具體的代碼實現，簡單的模擬了迭代器模式。

• Iterator類接口

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#import <Foundation/Foundation.h>                         @interface Iterator:NSObject -(id)First; -(id)Next; -(BOOL)IsDone; -(id)CurrentItem; @end

• Iterator類實現

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#import "Iterator.h"                       @implementation Iterator                       -(id)First{     return nil; } -(id)Next{     return nil; } -(BOOL)IsDone{     return NO; } -(id)CurrentItem{     return nil; }                       @end

• ConcreteIterator類接口

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#import "Iterator.h"                     @class ConcreteAggregate; @interface ConcreteIterator :Iterator{     ConcreteAggregate *myAggregate;     int current; } -(ConcreteIterator*)MyInit:(ConcreteAggregate*)aggregate; @end

• ConcreteIterator類實現

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#import "ConcreteIterator.h" #import "ConcreteAggregate.h"                   @implementation ConcreteIterator                   -(ConcreteIterator*)MyInit:(ConcreteAggregate*)aggregate{     myAggregate = aggregate;     return self; } -(id)First{    return [myAggregate GetObject:0]; } -(id)Next{     current++;     if(current< [myAggregate GetCount])         return [myAggregate GetObject:current];     else {         return nil;     } } -(BOOL)IsDone{    return current>= [myAggregate GetCount] ?YES:NO; } -(id)CurrentItem{    return [myAggregate GetObject:current]; }                   @end

• Aggregate類接口

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#import <Foundation/Foundation.h>                 @class Iterator; @interface Aggregate:NSObject -(Iterator*)CreateIterator; @end

• Aggregate類實現

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#import "Aggregate.h" #import "Iterator.h"               @implementation Aggregate -(Iterator*)CreateIterator{     return [[Iterator alloc]init]; } @end

• ConcreteAggregate類接口

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#import "Aggregate.h"             @interface ConcreteAggregate:Aggregate{     NSMutableArray *items; } -(int)GetCount; -(id)GetObject:(int)index; -(void)InsertObject:(id)Obj; @end

• ConcreteAggregate類實現

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#import "ConcreteAggregate.h" #import "Iterator.h"           @implementation ConcreteAggregate           -(id)init{     if(self == [super init]){         items = [NSMutableArray new];     }     return self; } -(Iterator*)CreateIterator{     return [[Iterator alloc]init]; } -(id)GetObject:(int)index{     return [items objectAtIndex:index]; } -(void)InsertObject:(id)Obj{     [items addObject:Obj]; } -(int)GetCount{     return [items count]; }           @end

• Main方法調用

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#import <Foundation/Foundation.h> #import "ConcreteAggregate.h" #import "Iterator.h" #import "ConcreteIterator.h"      int main (int argc, const char *argv[]) {     @autoreleasepool {     ConcreteAggregate *a = [[ConcreteAggregate alloc]init];                           [a InsertObject:@"張三"];         [a InsertObject:@"李四"];         [a InsertObject:@"王二"];         [a InsertObject:@"麻子"];         NSLog(@"Count:%d", [a GetCount]);         Iterator *i = [[ConcreteIterator alloc]MyInit:a];         while (![i IsDone]) {             NSLog(@"%@，請買票",[i CurrentItem]);             [i Next];         }     }     return 0; }

   好啦，上面的四個類型簡單實現了迭代器模式，其實迭代器模式就是分離了集合對象的遍歷行爲，抽象出一個迭代器類來負責，這樣既可以做到不暴露集合的內部結構，又可以讓外部代碼透明地訪問集合內部地數據。