C#从foreach语句中枚举元素看数组详解
前言 在foreach语句中使用枚举,可以迭代数组或集合中的元素,且无须知道集合中的元素的个数。如图显示了调用foreach方法的客户端和集合之间的关系。数组或集合实现带
先定义一个Person类,这个类有自动实现的属性Firstname和Lastname,以及从Object类重写ToString方法和继承泛型接口IEquatable以比较两个对象是否相等,实现泛型接口IComparer以比较两个对象用来排序。 public class Person : IEquatable<Person>,IComparable<Person> { public int Id { get; private set; } public string FirstName { get; set; } public string LastName { get; set; } public override string ToString() { return String.Format("{0},{1} {2}",Id,FirstName,LastName); } public bool Equals(Person other) { if (other == null) return base.Equals(other); return this.FirstName == other.FirstName && this.LastName == other.LastName; } public int CompareTo(Person other) { if (other == null) throw new ArgumentNullException("other"); int result = this.LastName.CompareTo(other.LastName); if (result == 0) { result = this.FirstName.CompareTo(other.FirstName); } return result; } } 创建一个三个元素的person数组,现对数组进行排序在用foreach循环访问数组中的元素并输出 Person[] persons = { new Person { FirstName = "Simen03",LastName = "Go" },new Person { FirstName = "Simen02",new Person { FirstName = "Simen01",LastName = "Go" } }; Array.Sort(persons); foreach (var person in persons) Console.WriteLine(person); 分析 // loop start (head: IL_009b) IL_008a: ldloc.2 IL_008b: ldloc.3 IL_008c: ldelem.ref IL_008d: stloc.s person IL_008f: ldloc.s person IL_0091: call void [mscorlib]System.Console::WriteLine(object) IL_0096: nop IL_0097: ldloc.3 IL_0098: ldc.i4.1 IL_0099: add IL_009a: stloc.3 IL_009b: ldloc.3 IL_009c: ldloc.2 IL_009d: ldlen IL_009e: conv.i4 IL_009f: blt.s IL_008a // end loop C#的foreach语句不会解析为IL代码中的foreach语句,C#编译器会把foreach语句转换为IEnumerable接口的方法和属性,foreach语句使用IEnumerator接口的方法和属性,迭代数组中的所有元素,为此,IEnumerator定义了Current属性,来返回光标所在的元素,该接口的 IEnumerator enumerator = persons.GetEnumerator(); while (enumerator.MoveNext()) { var person = enumerator.Current; Console.WriteLine(person); } 为了方便的创建枚举器,C#添加了yield语句,yield return 语句返回集合的一个元素,并移动到下一个元素,yield break 可停止迭代。使用迭代块,编译器会生成一个yield类型,其中包含一个状态机,如下代码段所示。yield 类型实现IEnumerator和IDisposable接口的属性和方法。在下面的例子中,可以把yield类型看作内部类Enumerator.外部类的 static void Main(string[] args) { var helloCollection = new HelloCollection(); foreach (string s in helloCollection) { Console.WriteLine(s); } } public class HelloCollection { public IEnumerator<string> GetEnumerator() { yield return "Hello"; yield return "World"; } } public class HelloCollectionOther { public IEnumerator GetEnumertor() { return new Enumerator(0); } public class Enumerator : IEnumerator<string>,IEnumerator,IDisposable { private int state; private string current; public Enumerator(int state) { this.state = state; } public string Current => throw new NotImplementedException(); object IEnumerator.Current { get { return current; } } public void Dispose() { throw new NotImplementedException(); } public bool MoveNext() { switch (state) { case 0:current = "hello"; state = 1; return true; case 1:current = "world"; state = 2; return true; case 2: break; } return false; } public void Reset() { throw new NotImplementedException(); } } } 总结 以上就是这篇文章的全部内容了,希望本文的内容对大家的学习或者工作能带来一定的帮助,如果有疑问大家可以留言交流,谢谢大家对编程小技巧的支持。 (编辑:李大同) 【声明】本站内容均来自网络,其相关言论仅代表作者个人观点,不代表本站立场。若无意侵犯到您的权利,请及时与联系站长删除相关内容! |