Converting from IEnumerable to List

Question

I want to convert from IEnumerable lt Contact gt  to List lt Contact gt    How can I do this

User · Answer

In case you re working with a regular old System Collections IEnumerable instead of IEnumerable lt T gt  you can use enumerable Cast lt object gt    ToList

User · Answer

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 lt string gt  stringEnumerable   null  StringBuilder csv   new StringBuilder    stringEnumerable ToNonNullList   ForEach str  gt  csv Append str  Append          Here is the extension method   public static List lt T gt  ToNonNullList lt T gt  this IEnumerable lt T gt  obj        return obj    null   new List lt T gt      obj ToList

User · Answer

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 lt string gt  provinces    provinces Cast lt string gt    ToList        If you re using Generic version IEnumerable lt T gt   The conversion is straight forward  Since both are generics  you can do like below   IEnumerable lt int gt  values   Enumerable Range 1  10   List lt int gt  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 lt int gt  values2   null  List lt int gt  valueList2   values2 ToList        Therefore as mentioned in the other answer  remember to do a null check before converting it to a List

User · Answer

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 lt int gt  enumerable   Enumerable Range 1  300   List lt int gt  asList   enumerable ToList

User · Answer

another way  List lt int gt  list new List lt int gt      IEnumerable lt int gt  enumerable  Enumerable Range 1  300      foreach  var item in enumerable              list add item

[c#] Converting from IEnumerable to List

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