迭代器模式
Provide a way to access the elements of an aggregate object sequentially without exposing its underlying representation.
提供一种方法顺序访问一个聚合对象中各个元素, 而又不需暴露该对象的内部表示。
迭代器模式是非常常见的设计模式之一, 适用条件很广, 需要访问聚合对象(数组、集合、列表等)的元素时, 即可使用迭代器模式。
public interface IIterator {
object CurrentItem();
void First();
bool IsDone();
void Next();
}
public interface IAggregate {
IIterator CreateIterator();
}
public class ConcreteIterator : IIterator {
private readonly object[] _aggregateItems;
private int _index;
public ConcreteIterator(object[] aggregateItems) {
this._aggregateItems = aggregateItems;
this._index = 0;
}
public object CurrentItem() {
return this._aggregateItems[this._index];
}
public void First() {
this._index = 0;
}
public bool IsDone() {
return this._index == this._aggregateItems.Length;
}
public void Next() {
this._index += 1;
}
}
public class ConcreateAggregate : IAggregate {
private readonly object[] _items;
public ConcreateAggregate(params object[] items) {
if (items != null) {
this._items = new object[items.Length];
for (var i = 0; i < items.Length; i++) {
this._items[i] = items[i];
}
}
}
public IIterator CreateIterator() {
return new ConcreteIterator(this._items);
}
}
class Client {
static void Main(string[] args) {
IAggregate aggregate = new ConcreateAggregate("Item1", "Item2", "Item3", "Item4");
IIterator iterator = aggregate.CreateIterator();
if (iterator.IsDone()) {
iterator.First();
}
while (!iterator.IsDone()) {
Console.WriteLine(iterator.CurrentItem());
iterator.Next();
}
Console.ReadKey();
}
}
.Net 内置了迭代器模式, 也称之为枚举器模式, 对应的接口类型为:
/// IEnumerator 对应 Iterator
public interface IEnumerator {
object Current;
bool MoveNext();
void Reset();
}
/// IEnumerable 与 Aggregate 对应
public interface IEnumerable {
IEnumerator GetEnumerator();
}
.Net 基础类库之中, 有很多类实现这两个接口, 比如: ArrayList, List, Collection, Hashtable 等。