Converting from IEnumerable to List [duplicate]

This question already has answers here: 开发者_开发问答 Casting IEnumerable<T> to List<T> (6 answers) Closed 6 years ago.

I want to convert from IEnumerable<Contact> to List<Contact>. How can I do this?

---

You can do this very simply using LINQ.

Make sure this using is at the top of your C# file:

using System.Linq;

Then use the ToList extension method.

Example:

IEnumerable<int> enumerable = Enumerable.Range(1, 300);
List<int> asList = enumerable.ToList();

---

In case you're working with a regular old System.Collections.IEnumerable instead of IEnumerable<T> you can use enumerable.Cast<object>().ToList()

---

If you're using an implementation of System.Collections.IEnumerable you can do like following to convert it to a List. The following uses Enumerable.Cast method to convert IEnumerable to a generic List.

// ArrayList implements IEnumerable interface
ArrayList _provinces = new System.Collections.ArrayList();
_provinces.Add("Western");
_provinces.Add("Eastern");

List<string> provinces = _provinces.Cast<string>().ToList();

---

If you're using Generic version IEnumerable<T>, The conversion is straight forward. Since both are generics, you can do like below,

IEnumerable<int> values = Enumerable.Range(1, 10);
List<int> valueList = values.ToList();

But if the IEnumerable is null, when you try to convert it to a List, you'll get an ArgumentNullException saying Value cannot be null.

IEnumerable<int> values2 = null;
List<int> valueList2 = values2.ToList();

Therefore as mentioned in the other answer, remember to do a null check before converting it to a List.

---

I use an extension method for this. My extension method first checks to see if the enumeration is null and if so creates an empty list. This allows you to do a foreach on it without explicitly having to check for null.

Here is a very contrived example:

IEnumerable<string> stringEnumerable = null;
StringBuilder csv = new StringBuilder();
stringEnumerable.ToNonNullList().ForEach(str=> csv.Append(str).Append(","));

Here is the extension method:

public static List<T> ToNonNullList<T>(this IEnumerable<T> obj)
{
    return obj == null ? new List<T>() : obj.ToList();
}

---

another way

List<int> list=new List<int>();

IEnumerable<int> enumerable =Enumerable.Range(1, 300);  

foreach (var item in enumerable )  
{     
  list.Add(item);  
}