利用索引器取值 赋值
案例1

c#
// 创建Test.cs  类
class Test {
  public string this[int index] {
    get {
      Console.WriteLine([index]);
      return 100；
    }
    set {
      Console.WriteLine([index]);
      Console.WriteLine(value);
    }
  }
}

c#
//使用 Program.cs
Test t = new Test();

t[9] = 200;
Console.WriteLine(t[9]);

案例2

c#
// 创建Test.cs  类
class Test {

  private string[] name = new string[10];

  public string this[int index] {
    get {
      return name[index];
    }
    set {
      name[index] = value;
    }
  }
}

c#
//使用 Program.cs
Test t = new Test();
t[0] = "张三";
t[1] = "李四"; //赋值

Console.WriteLine(t[0]);
Console.WriteLine(t[1]); //取值

案例3

c#
// 创建Week.cs  类
class Week {
  private string[] days = {
    "Mon",
    "Tues",
    "Wed",
    "Thu",
    "Fri",
    "Sat",
    "Sun"
  };

  // public int GetDay(string day)  //传递英文返回数值    
  private int GetDay(string day) //使用方法2索引时，需将public改为private
  {
    int i = 0; //开始传递
    foreach(string temp in days) {
      if (temp == day) return i + 1; //找到索引
      i++;
    }
    return -1;
  }

  public int this[string day] {
    get {
      return GetDay(day); //调用上面的方法
    }
  }
}

c#
//使用 Program.cs
//方法1
Week w = new Week();
Console.WriteLine(w.GetDay("Thu"));
//方法2
Console.WriteLine(w["Sat"]);