How to cast Generic Lists dynamically in C#?

Question

I'm trying to cast List<object> to List<string> dynamically. I've tried several ways, but I can't find a solution. This is a small sample that shows the problem:

List<object> listObject = new List<object>();
listObject.Add("ITEM 1");
listObject.Add("ITEM 2");
listObject.Add("ITEM 3");

List<string> listString = ¿¿listObject??;

Thanks in advance!

Answer 1

If you can use LINQ then the Cast method will do what you need:

List<string> listString = listObject.Cast<string>().ToList();

You can also use the ConvertAll method, as Stan points out in his answer:

List<string> listString = listObject.ConvertAll(x => (string)x);

If you're not using C#3 then you'll need to use the "old" delegate syntax rather than a lambda:

List<string> listString =
    listObject.ConvertAll(delegate(object x) { return (string)x; });

Answer 2

If you're using .NET 3.5 you can use, this way you don't have to do an extra ToList(). You can also supply your own converter if you need to convert advanced objects.

 List<string> listString = listObject.ConvertAll(x=> x as String);

If you can't use LINQ you can do this

foreach(object item in listObject)
{
  string convertedItem = item as String;
  if(convertedItem != null)
       listString.Add(convertedItem);
}

Answer 3

I don't think you can do it one step. Instead, try something like this:

  List<object> listObject = new List<object>();
  listObject.Add( "ITEM 1" );
  listObject.Add( "ITEM 2" );
  listObject.Add( "ITEM 3" );

  List<string> lstStr = new List<string>( listObject.Count );

  foreach ( object obj in listObject )
  {
   lstStr.Add( obj.ToString() );
  }

Answer 4

List<string> listString = (from o in listObject select (string)o).ToList();

Answer 5

How bout this:

public static List<T> ConvertToGenericList<T>(IList listOfObjects)
{
    List<T> items = new List<T>();

    for (int i = 0; i < listOfObjects.Count; i++)
    {
        items.Add((T)listOfObjects[i]);
    }
     return items;
}

Usage:

List<object> listObject = new List<object>();
listObject.Add("ITEM 1");
listObject.Add("ITEM 2");
listObject.Add("ITEM 3");
List<string> listString = Converter.ConvertToGenericList<string>(listObject);