C# 索引器基础

索引器在语法上方便您创建客户端应用程序可将其作为数组访问的类、结构或接口。

要声明类或结构上的索引器，请使用 this 关键字，如下例所示：

public int this[int index]    // Indexer declaration
{
    // get and set accessors
}


实例1

class TempRecord
{
    // Array of temperature values
    private float[] temps = new float[10] { 56.2F, 56.7F, 56.5F, 56.9F, 58.8F,
                                            61.3F, 65.9F, 62.1F, 59.2F, 57.5F };

    // To enable client code to validate input
    // when accessing your indexer.
    public int Length
    {
        get { return temps.Length; }
    }
    // Indexer declaration.
    // If index is out of range, the temps array will throw the exception.
    public float this[int index]
    {
        get
        {
            return temps[index];
        }

        set
        {
            temps[index] = value;
        }
    }
}

class MainClass
{
    static void Main()
    {
        TempRecord tempRecord = new TempRecord();
        // Use the indexer's set accessor
        tempRecord[3] = 58.3F;
        tempRecord[5] = 60.1F;

        // Use the indexer's get accessor
        for (int i = 0; i < 10; i++)
        {
            System.Console.WriteLine("Element #{0} = {1}", i, tempRecord[i]);
        }

        // Keep the console window open in debug mode.
        System.Console.WriteLine("Press any key to exit.");
        System.Console.ReadKey();

    }
}
/* Output:
        Element #0 = 56.2
        Element #1 = 56.7
        Element #2 = 56.5
        Element #3 = 58.3
        Element #4 = 58.8
        Element #5 = 60.1
        Element #6 = 65.9
        Element #7 = 62.1
        Element #8 = 59.2
        Element #9 = 57.5
    */

实例2

// Using a string as an indexer value
class DayCollection
{
    string[] days = { "Sun", "Mon", "Tues", "Wed", "Thurs", "Fri", "Sat" };

    // This method finds the day or returns -1
    private int GetDay(string testDay)
    {

        for (int j = 0; j < days.Length; j++)
        {
            if (days[j] == testDay)
            {
                return j;
            }
        }

        throw new System.ArgumentOutOfRangeException(testDay, "testDay must be in the form \"Sun\", \"Mon\", etc");
    }

    // 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"]);

        // Raises ArgumentOutOfRangeException
        System.Console.WriteLine(week["Made-up Day"]);

        // Keep the console window open in debug mode.
        System.Console.WriteLine("Press any key to exit.");
        System.Console.ReadKey();
    }
}
// Output: 5