iOS App設計模式開發中對迭代器模式的使用示例

2020-07-26 03:24:02

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何為迭代器模式？

迭代器提供了一種順序訪問集合對象中元素的方法，而無需暴漏結構的底層表示和細節。遍歷集合中元素的職能從集合本身轉移到迭代器對象。迭代器定義了一個用于訪問集合元素并記錄當前元素的接口。不同的迭代器可以執行不同的策略。

例子

說了這么多，下面給大家展示一下類關系圖。

2016330165811106.jpg (385×280)

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，看起來是為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。

注意：本文所有代碼均在ARC環境下編譯通過。

Iterator類接口

復制代碼代碼如下:

#import <Foundation/Foundation.h>

@interface Iterator:NSObject
-(id)First;
-(id)Next;
-(BOOL)IsDone;
-(id)CurrentItem;
@end

Iterator類實現

復制代碼代碼如下:

#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

復制代碼代碼如下:

#import "Iterator.h"

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

ConcreteIterator類實現

復制代碼代碼如下:

#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

復制代碼代碼如下:

#import <Foundation/Foundation.h>

@class Iterator;
@interface Aggregate:NSObject
-(Iterator*)CreateIterator;
@end

Aggregate類實現

復制代碼代碼如下:

#import "Aggregate.h"
#import "Iterator.h"

@implementation Aggregate
-(Iterator*)CreateIterator{
return [[Iterator alloc]init];
}
@end

ConcreteAggregate類接口

復制代碼代碼如下:

#import "Aggregate.h"

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

ConcreteAggregate類實現

復制代碼代碼如下:

#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

復制代碼代碼如下:

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;
}