关于ArrayList（）用法的实践理解

一、将数据Point[] arrPt 做为参数传给ArrayList.Add()时，只能使用arrlst[0]，不能使用arrlst[1]、arrlst[2]等等，这样会出错；因为Point[] arrPt数组是做为一个引用传入给ArrayList的，所以显示出来的结果也是System.Drawing.Point[]类型。

实例如下：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Drawing;
using System.Windows.Forms;
using System.Collections;

namespace ArrayListDemo
{
    class Program
    {
        static void Main(string[] args)
        {
            
            Point[] arrPt = { new Point(1,2),new Point(2,3),new Point(3,4),new Point(4,5),new Point(5,6)};
            //Point[] arrpoint = {new Point(2,1),new Point(3,2),new Point(4,3) };

            ArrayList arrlst = new ArrayList();
            arrlst.Add(arrPt);
            //arrlst.Add(arrpoint);

            //Console.WriteLine(((Point[])arrlst[0])[1]);
            //Console.WriteLine(arrPt[0]);
            //Console.WriteLine(arrlst);
            Console.WriteLine(arrlst[0]);
            Console.WriteLine(arrlst[1]);
            Console.WriteLine(arrlst[2]);
        }
    }
}

 

从上图结果可以看出，第27行，索引超出范围并报错。那如果在ArrayList()实例中正确显示出Point[] arrPt数组中的每个元素呢？应该使用如下方法：

　　　  Console.WriteLine(((Point[])arrlst[0])[0]);
            Console.WriteLine(((Point[])arrlst[0])[1]);
            Console.WriteLine(((Point[])arrlst[0])[2]);
            Console.WriteLine(((Point[])arrlst[0])[3]);
            Console.WriteLine(((Point[])arrlst[0])[4]);

因为arrlst[0]是object类型，所以使用((Point[])arrlst[0])转换为Point[]数组类型，然后再使用(Point[])arrlst[0])[0]等数组索引就可以访问Point[] arrPt数组中的每个元素了；

具体实例如下：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Drawing;
using System.Windows.Forms;
using System.Collections;

namespace ArrayListDemo
{
    class Program
    {
        static void Main(string[] args)
        {
            
            Point[] arrPt = { new Point(1,2),new Point(2,3),new Point(3,4),new Point(4,5),new Point(5,6)};
            //Point[] arrpoint = {new Point(2,1),new Point(3,2),new Point(4,3) };

            ArrayList arrlst = new ArrayList();
            arrlst.Add(arrPt);
            //arrlst.Add(arrpoint);

            Console.WriteLine(((Point[])arrlst[0])[0]);
            Console.WriteLine(((Point[])arrlst[0])[1]);
            Console.WriteLine(((Point[])arrlst[0])[2]);
            Console.WriteLine(((Point[])arrlst[0])[3]);
            Console.WriteLine(((Point[])arrlst[0])[4]);
            
            //Console.WriteLine(arrlst);
            Console.WriteLine(arrlst[0]);
            //Console.WriteLine(arrlst[1]);
            //Console.WriteLine(arrlst[2]);
        }
    }
}

 

 二、增加第29行代码，Console.WriteLine(arrlst);

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Drawing;
using System.Windows.Forms;
using System.Collections;

namespace ArrayListDemo
{
    class Program
    {
        static void Main(string[] args)
        {
            
            Point[] arrPt = { new Point(1,2),new Point(2,3),new Point(3,4),new Point(4,5),new Point(5,6)};
            //Point[] arrpoint = {new Point(2,1),new Point(3,2),new Point(4,3) };

            ArrayList arrlst = new ArrayList();
            arrlst.Add(arrPt);
            //arrlst.Add(arrpoint);

            Console.WriteLine(((Point[])arrlst[0])[0]);
            Console.WriteLine(((Point[])arrlst[0])[1]);
            Console.WriteLine(((Point[])arrlst[0])[2]);
            Console.WriteLine(((Point[])arrlst[0])[3]);
            Console.WriteLine(((Point[])arrlst[0])[4]);
            
            Console.WriteLine(arrlst);
            Console.WriteLine(arrlst[0]);
            //Console.WriteLine(arrlst[1]);
            //Console.WriteLine(arrlst[2]);
        }
    }
}

 

对应的显示结果为：
System.Collections.ArrayList

第三，增加第17和第31行，Point[] arrpoint = {new Point(2,1),new Point(3,2),new Point(4,3) };   Console.WriteLine(arrlst[1]); arrlst.Add(arrpoint)；

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Drawing;
using System.Windows.Forms;
using System.Collections;

namespace ArrayListDemo
{
    class Program
    {
        static void Main(string[] args)
        {
            
            Point[] arrPt = { new Point(1,2),new Point(2,3),new Point(3,4),new Point(4,5),new Point(5,6)};
            Point[] arrpoint = {new Point(2,1),new Point(3,2),new Point(4,3) };

            ArrayList arrlst = new ArrayList();
            arrlst.Add(arrPt);
            arrlst.Add(arrpoint);

            Console.WriteLine(((Point[])arrlst[0])[0]);
            Console.WriteLine(((Point[])arrlst[0])[1]);
            Console.WriteLine(((Point[])arrlst[0])[2]);
            Console.WriteLine(((Point[])arrlst[0])[3]);
            Console.WriteLine(((Point[])arrlst[0])[4]);
            
            Console.WriteLine(arrlst);
            Console.WriteLine(arrlst[0]);
            Console.WriteLine(arrlst[1]);
            //Console.WriteLine(arrlst[2]);
        }
    }
}