How to convert an ArrayList to a strongly typed ge

问题:

See the code sample below. I need the ArrayList to be a generic List. I don't want to use foreach.

ArrayList arrayList = GetArrayListOfInts();  
List<int> intList = new List<int>();  

//Can this foreach be condensed into one line?  
foreach (int number in arrayList)  
{  
    intList.Add(number);  
}  
return intList;    

回答1:

Try the following

var list = arrayList.Cast<int>().ToList();

This will only work though using the C# 3.5 compiler because it takes advantage of certain extension methods defined in the 3.5 framework.

回答2:

This is inefficient (it makes an intermediate array unnecessarily) but is concise and will work on .NET 2.0:

List<int> newList = new List<int>(arrayList.ToArray(typeof(int)));

回答3:

How about using an extension method?

From http://www.dotnetperls.com/convert-arraylist-list:

using System;
using System.Collections;
using System.Collections.Generic;

static class Extensions
{
    /// <summary>
    /// Convert ArrayList to List.
    /// </summary>
    public static List<T> ToList<T>(this ArrayList arrayList)
    {
        List<T> list = new List<T>(arrayList.Count);
        foreach (T instance in arrayList)
        {
            list.Add(instance);
        }
        return list;
    }
}

回答4:

In .Net standard 2 using Cast<T> is better way:

ArrayList al = new ArrayList();
al.AddRange(new[]{"Micheal", "Jack", "Sarah"});
List<int> list = al.Cast<int>().ToList();

Cast and ToList are extension methods in the System.Linq.Enumerable class.