[c#] Converting from IEnumerable to List

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

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 IEnumberable 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 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);  
}