How do I clone a generic list in C#?

If your elements are value types, then you can just do:

List<YourType> newList = new List<YourType>(oldList);

However, if they are reference types and you want a deep copy (assuming your elements properly implement ICloneable), you could do something like this:

List<ICloneable> oldList = new List<ICloneable>();
List<ICloneable> newList = new List<ICloneable>(oldList.Count);

oldList.ForEach((item) =>
    {
        newList.Add((ICloneable)item.Clone());
    });

Obviously, replace ICloneable in the above generics and cast with whatever your element type is that implements ICloneable.

If your element type doesn't support ICloneable but does have a copy-constructor, you could do this instead:

List<YourType> oldList = new List<YourType>();
List<YourType> newList = new List<YourType>(oldList.Count);

oldList.ForEach((item)=>
    {
        newList.Add(new YourType(item));
    });

Personally, I would avoid ICloneable because of the need to guarantee a deep copy of all members. Instead, I'd suggest the copy-constructor or a factory method like YourType.CopyFrom(YourType itemToCopy) that returns a new instance of YourType.

Any of these options could be wrapped by a method (extension or otherwise).

You can use an extension method.

static class Extensions
{
    public static IList<T> Clone<T>(this IList<T> listToClone) where T: ICloneable
    {
        return listToClone.Select(item => (T)item.Clone()).ToList();
    }
}

For a shallow copy, you can instead use the GetRange method of the generic List class.

List<int> oldList = new List<int>( );
// Populate oldList...

List<int> newList = oldList.GetRange(0, oldList.Count);

Quoted from: Generics Recipes

public static object DeepClone(object obj) 
{
    object objResult = null;

    using (var ms = new MemoryStream())
    {
        var bf = new BinaryFormatter();
        bf.Serialize(ms, obj);

        ms.Position = 0;
        objResult = bf.Deserialize(ms);
     }

     return objResult;
}

This is one way to do it with C# and .NET 2.0. Your object requires to be [Serializable()]. The goal is to lose all references and build new ones.