本文較為詳細的描述了重載運算符的方法。一般來說，重載運算符在實際的項目開發中會經常的用到，但如果某些自定義類型通過簡短幾行代碼重載一些常用的運算符（如：+-*/），就能讓編程工作帶來方便；重載運算符就是告訴編譯器+-*/等運算符對于自定義類型進行什么樣的操作，在代碼中需要注意幾點。
一、盡可能的不要改變運算符本身的含義
二、所有的運算符重載都必須聲明為public和static
三、不同于擴展方法，所重載的方法必須是在被重載的類型內部，且用關鍵字operator
C#中的兩個字符串相加，實際上是連接兩個字符串，假如有兩個EmployeeDetail類型相加得到一個EmployeeCollection集合，如：
EmployeeDetail a,b;....EmployeeCollection collection = a+b;
當編譯器遇到上面的代碼時就會自動調用EmployeeDetail類上標有operator +的靜態方法，并將兩個操作數a和b作為參數傳遞給對于的方法，該方法需要方法一個值賦給collection，假設EmployeeDetail類有三個屬性分別是FirstName,MiddleName,LastName，還重寫了ToString方法返回一個連接這三個名稱的字符串，代碼如：
[Serializable] public class EmployeeDetail { public string FirstName { get; set; } public string MiddleName { get; set; } public string LastName { set;get; } public override string ToString() { return string.Format("{0}{1}{2}{3}{4}", FirstName, string.IsNullOrWhiteSpace(MiddleName) ? null : "." , MiddleName , string.IsNullOrWhiteSpace(LastName) ? null : ".", LastName).Trim(); } }下面的代碼為“+”運算符提供支持的運算符重載：
public static EmployeeCollection operator +(EmployeeDetail a, EmployeeDetail b){ return new EmployeeCollection() { a, b };}OK，給EmployeeDetail類加上這樣的一個方法之后，我們就可以像下面那個寫代碼了：
EmployeeCollection collection = new EmployeeDetail(){FirstName="Jackson",LastName="Bruce"} + new EmployeeDetail(){FirstName="Michael",LastName="Jackson"} ;但是這樣還不夠完美，假設a，b，c都是EmployeeDetail類型，下面的代碼會拋出一個編譯錯誤：
EmployeeCollection collection = a + b + c;
為什么編譯不通過呢？大家都知道除了賦值運算符外表達式是從左到右執行的，a+b返回的是EmployeeCollection類型，EmployeeCollection類型并沒有重載“+”運算符，編譯器不知道要執行什么操作，所以我們還有下面的兩個方法：
public static EmployeeCollection operator +(EmployeeCollection collection, EmployeeDetail a){ collection.Add(a); return collection;}public static EmployeeCollection operator +(EmployeeDetail a, EmployeeCollection collection){ return collection + a;}這看起來似乎已經很完美了，但我們還可以做得更好一些，比如要將字符串“Jackson.Bruce”直接隱式轉換為EmployeeDetail類型，也就是說可以將“Jackson.Bruce"這種格式的字符串直接賦給EmployeeDetail類型的對象，如：EmployeeDetail employee= “Jackson.Bruce"，那么就需要重載隱式類型轉換運算符了，代碼如下：
/// <summary>/// 隱式類型轉換/// </summary>/// <param name="name"></param>/// <returns></returns>public static implicit operator EmployeeDetail(string name){ /// 其實在這里可以寫一個正則表達式檢查name的字符串格式是否合法，如果不合法就拋出異?！ ?// string[] arr; return string.IsNullOrWhiteSpace(name) ? null : new EmployeeDetail() { FirstName = (arr = name.Trim().Split('.'))[0] , LastName = arr.Length > 1 ? arr[arr.Length > 2 ? 2 : 1] : null, MiddleName = arr.Length > 2 ? arr[1] : null };}public static EmployeeCollection operator +(EmployeeDetail a, string b){ return new EmployeeCollection() { a, b };}看到這里您是不是迫不及待地想試試看，OK寫個控制臺程序來測試一下：
static void Main(string[] args){ EmployeeDetail employee = "Jackson.Bruce"; Console.WriteLine("FirstName={0},MiddleNam={1},LastName={2}", employee.FirstName, employee.MiddleName, employee.LastName); Console.WriteLine("toString={0}", employee); Console.WriteLine(); EmployeeCollection collection = "Michael.Jackson" + employee; collection += "Bruce.Lee"; foreach (var e in collection) { Console.WriteLine(e); } Console.WriteLine(); collection -= employee; foreach (var e in collection) { Console.WriteLine(e); } Console.WriteLine("===end==="); Console.Read();}運行結果如下圖所示：
全部代碼，里面還包含其他運算符的重載，這里就不再介紹了，趕緊動手測試一下吧：
using System;using System.Collections.Generic;using System.Linq;using System.Text;namespace 重載運算符{ [Serializable] public class EmployeeDetail { public string FirstName { get; set; } public string MiddleName { get; set; } public string LastName { set;get; } public static EmployeeCollection operator +(EmployeeDetail a, EmployeeDetail b) { return new EmployeeCollection() { a, b }; } public static EmployeeCollection operator +(EmployeeCollection collection, EmployeeDetail a) { collection.Add(a); return collection; } public static EmployeeCollection operator +(EmployeeDetail a, EmployeeCollection collection) { return collection + a; } /// <summary> /// 隱式類型轉換 /// </summary> /// <param name="name"></param> /// <returns></returns> public static implicit operator EmployeeDetail(string name) { string[] arr; return string.IsNullOrWhiteSpace(name) ? null : new EmployeeDetail() { FirstName = (arr = name.Trim().Split('.'))[0] , LastName = arr.Length > 1 ? arr[arr.Length > 2 ? 2 : 1] : null, MiddleName = arr.Length > 2 ? arr[1] : null }; } public static EmployeeCollection operator +(EmployeeDetail a, string b) { return new EmployeeCollection() { a, b }; } public override string ToString() { return string.Format("{0}{1}{2}{3}{4}", FirstName, string.IsNullOrWhiteSpace(MiddleName) ? null : "." , MiddleName , string.IsNullOrWhiteSpace(LastName) ? null : ".", LastName).Trim(); } } public class EmployeeCollection : List<EmployeeDetail> { public static EmployeeCollection operator +(EmployeeCollection a, string b) { a.Add(b); return a; } public static EmployeeCollection operator +(string b, EmployeeCollection a) { return a + b; } public static EmployeeCollection operator -(EmployeeCollection a, EmployeeDetail b) { a.Remove(b); return a; } } class Program { static void Main(string[] args) { EmployeeDetail employee = "Jackson.Bruce"; Console.WriteLine("FirstName={0},MiddleNam={1},LastName={2}", employee.FirstName, employee.MiddleName, employee.LastName); Console.WriteLine("toString={0}", employee); Console.WriteLine(); EmployeeCollection collection = "Michael.Jackson" + employee; collection += "Bruce.Lee"; foreach (var e in collection) { Console.WriteLine(e); } Console.WriteLine(); collection -= employee; foreach (var e in collection) { Console.WriteLine(e); } Console.WriteLine("===end==="); Console.Read(); } }}新聞熱點
疑難解答
