public animal this[int index]|索引器的使用

学习如何使用索引器,索引器的使用是public 类型 this[int index]{get{};set{}} ,访问通过类的实例（对象）加[i]，

例如animal[i],就像访问数组一样，其实就是类的数组访问的使用书写。

使用详情请看msdn。

例子如下：

class IndexerClass
{
    private int[] arr = new int[];
    public int this[int index]   // Indexer declaration
    {
        get
        {
            // Check the index limits.
            if (index <  || index >= )
            {
                return ;
            }
            else
            {
                return arr[index];
            }
        }
        set
        {
            if (!(index <  || index >= ))
            {
                arr[index] = value;
            }
        }
    }
}

class MainClass
{
    static void Main()
    {
        IndexerClass test = new IndexerClass();
        // Call the indexer to initialize the elements #3 and #5.
        test[] = ;
        test[] = ;
        for (int i = ; i <= ; i++)
        {
            System.Console.WriteLine("Element #{0} = {1}", i, test[i]);
        }
    }
}

class DayCollection
{
    string[] days = { "Sun", "Mon", "Tues", "Wed", "Thurs", "Fri", "Sat" };

    // This method finds the day or returns -1
    private int GetDay(string testDay)
    {
        int i = ;
        foreach (string day in days)
        {
            if (day == testDay)
            {
                return i;
            }
            i++;
        }
        return -;
    }

    // The get accessor returns an integer for a given string
    public int this[string day]
    {
        get
        {
            return (GetDay(day));
        }
    }
}

class Program
{
    static void Main(string[] args)
    {
        DayCollection week = new DayCollection();
        System.Console.WriteLine(week["Fri"]);
        System.Console.WriteLine(week["Made-up Day"]);
    }
}