iOS App设计模式开发中对迭代器模式的使用示例

2020-07-26 03:24:02

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何为迭代器模式？

迭代器提供了一种顺序访问集合对象中元素的方法，而无需暴漏结构的底层表示和细节。遍历集合中元素的职能从集合本身转移到迭代器对象。迭代器定义了一个用于访问集合元素并记录当前元素的接口。不同的迭代器可以执行不同的策略。

例子

说了这么多，下面给大家展示一下类关系图。

2016330165811106.jpg (385×280)

上图中Client的右边是迭代器，左边是具体迭代的类型，在迭代器内部对具体需要迭代的类型进行了引用，还算不难理解吧，呵呵。其实，看起来是为了对具体类型进行解耦。好啦，下面给出具体的代码实现，简单的模拟了迭代器模式。

注意：本文所有代码均在ARC环境下编译通过。

Iterator类接口

复制代码代码如下:

#import <Foundation/Foundation.h>

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

Iterator类实现

复制代码代码如下:

#import "Iterator.h"

@implementation Iterator

-(id)First{
    return nil;
}
-(id)Next{
    return nil;
}
-(BOOL)IsDone{
    return NO;
}
-(id)CurrentItem{
    return nil;
}
@end

ConcreteIterator类接口

复制代码代码如下:

#import "Iterator.h"

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

ConcreteIterator类实现

复制代码代码如下:

#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类接口

复制代码代码如下:

#import <Foundation/Foundation.h>

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

Aggregate类实现

复制代码代码如下:

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

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

ConcreteAggregate类接口

复制代码代码如下:

#import "Aggregate.h"

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

ConcreteAggregate类实现

复制代码代码如下:

#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方法调用

复制代码代码如下:

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:@"张三"];
         [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(@"%@，请买票",[i CurrentItem]);
             [i Next];
         }
     }
     return 0;
}