C＃|获取或设置ArrayList中指定索引处的元素

ArrayList.Item [Int32]属性用于获取或设置ArrayList中指定索引处的元素。

句法：

public virtual object this[int index] { get; set; }

在这里， index是要获取或设置的元素的从零开始的索引。

返回值：返回指定索引处的Object类型的元素。

异常：如果索引小于零或等于或大于Count，则此属性将引发ArgumentOutOfRangeException 。

下面的程序说明了上面讨论的属性的用法：

范例1：

// C# code to get or set the element at
// the specified index in ArrayList
using System;
using System.Collections;
  
class GFG {
  
    // Driver code
    public static void Main()
    {
  
        // Creating an ArrayList
        ArrayList myList = new ArrayList();
  
        // Adding elements to ArrayList
        myList.Add("A");
        myList.Add("B");
        myList.Add("C");
        myList.Add("D");
        myList.Add("E");
        myList.Add("F");
  
        // Displaying the elements
        // in the ArrayList
        foreach(string str in myList)
        {
            Console.WriteLine(str);
        }
  
        Console.WriteLine("After Item[int32] Property: ");
  
        // setting the value at index 2
        myList[2] = "Z";
  
        // Displaying the elements
        // in the ArrayList
        foreach(string str in myList)
        {
            Console.WriteLine(str);
        }
    }
}

输出：

A
B
C
D
E
F
After Item[int32] Property: 
A
B
Z
D
E
F

范例2：

// C# code to get or set the element at
// the specified index in ArrayList
using System;
using System.Collections;
using System.Collections.Generic;
  
class GFG {
  
    // Driver code
    public static void Main()
    {
  
        // Creating an ArrayList
        ArrayList myList = new ArrayList();
  
        // Adding elements to ArrayList
        // Adding elements to ArrayList
        myList.Add(2);
        myList.Add(4);
        myList.Add(6);
        myList.Add(8);
        myList.Add(10);
        myList.Add(12);
        myList.Add(14);
        myList.Add(16);
        myList.Add(18);
        myList.Add(20);
  
        // Displaying the elements
        // in the ArrayList
        foreach(int i in myList)
        {
            Console.WriteLine(i);
        }
  
        Console.WriteLine("After Item[int32] Property: ");
  
        // setting the value at index 8
        // this will give error as index
        // is greater than count
        myList[10] = 56;
  
        // Displaying the elements
        // in the ArrayList
        foreach(int j in myList)
        {
            Console.WriteLine(j);
        }
    }
}

运行时错误：

Unhandled Exception:
System.ArgumentOutOfRangeException: Index was out of range. Must be non-negative and less than the size of the collection.
Parameter name: index

参考：

• https://docs.microsoft.com/zh-cn/dotnet/api/system.collections.arraylist.item?view=netframework-4.7.2