iOS开发-迭代器模式

迭代器模式（Iterator），提供一种方法顺序访问一个聚合对象中的各种元素，而又不暴露该对象的内部表示。开发过程中，我们可能需要针对不同的需求，可能需要以不同的方式来遍历整个整合对象，但是我们不希望遍历的对象内部存储结构被外部知道，那么可以将对象包装成一个迭代器，迭代器中定义中遍历对象的方法下一个，是否存在下一个对象，删除等遍历需要的统一接口，迭代器在Java和.NET使用的比较多，自定义实现叶非常简单，可以简单的看一下迭代器模式的UML类图。

迭代器定义基本的遍历操作方法，容器定义公共的创建迭代器的方法，子类负责实现具体需要引用的迭代器，我们可以假设图书馆是一个抽象容器，图书馆下面分为国家图书馆和个人图书馆，个人图书馆存储书籍的方式是可变数组存储书籍，国家图书馆数据存储书籍，分别创建不同的迭代器；

BookLibrary容器接口:

@protocol BoolLibraryProtocol<NSObject>
 
@optional
-(Iterator *)createIterator;
 
@end
 
@interface BookLibrary : NSObject<BoolLibraryProtocol>
 
@end

CountryBookLibrary国家图书馆:

@interface CountryBookLibrary()
 
@property  (strong,nonatomic)  NSArray  *bookArr;
 
@end
 
@implementation CountryBookLibrary
 
- (instancetype)init
{
    self = [super init];
    if (self) {
       Book  *one=[self addBook:@"CountryBookLibrary" price:10];
       Book *next=[self addBook:@"博客园-FlyElephant" price:20];
        self.bookArr=@[one,next];
    }
    return self;
}
 
-(Iterator *)createIterator{
    return [[CountryIterator alloc]initWithData:self.bookArr];
}
 
-(Book *)addBook:(NSString *)bookName  price:(float)price{
    Book *book=[[Book alloc]init];
    book.bookName=bookName;
    book.price=price;
    return  book;
}
 
@end

PersonLibraryBook个人图书馆:

@interface PersonBookLibray()
 
@property  (strong,nonatomic)  NSMutableArray  *books;
 
@end
 
@implementation PersonBookLibray
 
- (instancetype)init
{
    self = [super init];
    if (self) {
        [self addBook:@"PersonIterator" price:100];
        [self addBook:@"博客园-FlyElephant" price:200];
    }
    return self;
}
 
-(Iterator *)createIterator{
    return [[PersonIterator alloc]initWithData:self.books];
}
 
-(void)addBook:(NSString *)bookName  price:(float)price{
    Book *book=[[Book alloc]init];
    book.bookName=bookName;
    book.price=price;
    [self.books addObject:book];
}
 
#pragma mark - getter and  setter
-(NSMutableArray *)books{
    if (!_books) {
        _books=[[NSMutableArray alloc]init];
    }
    return _books;
}
 
@end

迭代器Iterator:

@protocol IteratorProtocol <NSObject>
 
@optional
-(Boolean)hasNext;
 
@optional
-(id)next;
 
@end
 
@interface Iterator : NSObject<IteratorProtocol>
 
@end

国家图书馆引用的迭代器:

@interface  CountryIterator()
 
@property  (strong,nonatomic)  NSArray  *arr;
@property  (assign,nonatomic)  NSInteger position;
 
@end
 
@implementation CountryIterator
 
-(instancetype)initWithData:(NSArray *)data{
    self=[super init];
    if (self) {
        self.arr=data;
    }
    return self;
}
 
-(Boolean)hasNext{
    if (self.position>=[self.arr count]||!self.arr[self.position]) {
        return false;
    }else{
        return true;
    }
}
 
-(id)next{
    Book *book=self.arr[self.position];
    self.position+=1;
    return book;
}
 
@end

个人图书馆引用的迭代器:

@interface PersonIterator()
 
@property (assign,nonatomic)  NSInteger            position;
@property (strong,nonatomic)  NSMutableArray       *mutableArr;
 
@end
 
@implementation PersonIterator
 
-(instancetype)initWithData:(NSMutableArray *)data{
    self=[super init];
    if (self) {
        self.mutableArr=data;
    }
    return self;
}
 
-(Boolean)hasNext{
    if (self.position>=[self.mutableArr count]||![self.mutableArr objectAtIndex:self.position]) {
        return false;
    }else{
        return true;
    }
}
 
-(id)next{
    Book *book=[self.mutableArr objectAtIndex:self.position];
    self.position+=1;
    return book;
}
 
@end

实际调用:

-(void)iteratorDesign{
    BookLibrary *personLibrary=[[PersonBookLibray alloc]init];
    Iterator    *personIterator=[personLibrary createIterator];
    [self logLibraryInfo:personIterator];
     
    BookLibrary *countryLibrary=[[CountryBookLibrary alloc]init];
    Iterator    *countryIterator=[countryLibrary createIterator];
    [self logLibraryInfo:countryIterator];
}
 
-(void)logLibraryInfo:(Iterator *)iterator{
    while ([iterator hasNext]) {
        Book *book=[iterator next];
        NSLog(@"书名:%@--价格:%ld",book.bookName,book.price);
    }
}