C# |为列表创建只读包装
列表< T >。AsReadOnly 方法用于获取当前集合的只读readonly collectionT3】包装。
语法:
公共系统。collections . object model . readonlycollectionas readonly()；
返回值:返回一个对象，该对象作为当前 列表< T > 的只读包装器。
示例:
// C# code to create a read-only
// wrapper for the List<T>
using System;
using System.Collections.Generic;
class GFG {
// Driver code
public static void Main()
{
// Creating an List<T> of Integers
List<int> mylist = new List<int>();
// Adding elements to List
mylist.Add(17);
mylist.Add(19);
mylist.Add(21);
mylist.Add(9);
mylist.Add(75);
mylist.Add(19);
mylist.Add(73);
Console.WriteLine("Before Wrapping: ");
// Displaying the elements
// in the mylist
foreach(int i in mylist)
{
Console.WriteLine(i);
}
// Creating a Read-Only packing
// around the List
IList<int> readlist = mylist.AsReadOnly();
Console.WriteLine("After Wrapping: ");
// Displaying the elements
// of Read-Only Collection
foreach(int j in readlist)
{
Console.WriteLine(j);
}
// You can add elements to
// the original List i.e. mylist
Console.WriteLine("Adding new element to mylist: ");
mylist.Add(35);
// Displaying the elements
// in the mylist
foreach(int k in mylist)
{
Console.WriteLine(k);
}
// But you cannot add elements
// into the Read-Only Collection
Console.WriteLine("Trying to add new element into readlist:");
// it will give error
readlist.Add(34);
}
}
输出:
Before Wrapping:
17
19
21
9
75
19
73
After Wrapping:
17
19
21
9
75
19
73
Adding new element to mylist:
17
19
21
9
75
19
73
35
Trying to add new element into readlist:
运行时错误:
未处理异常: 系统。NotSupportedException:集合是只读的。
参考:
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