CODEWITHSUNDEEP
c#.netgenericslistcasting
user161037
user161037

Reputation:

How to cast Generic Lists dynamically in C#?

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!

Upvotes: 9

Views: 11557

Answers (6)

Riccardo G
Riccardo G

Reputation: 1

My first post... Hope usefull looks work in my project...

        public  dynamic ConvertList(Type CallingType)
    {

        dynamic DynamicList;

        if (CallingType == TypeOfValue)
        {
            Type d1 = typeof(List<>);

            Type[] typeArgs = { TypeOfValue };

            Type DynamicListType = d1.MakeGenericType(typeArgs);


            object DynamicListObj = Activator.CreateInstance(DynamicListType);


            DynamicList = Convert.ChangeType(DynamicListObj, DynamicListType);


            foreach (object ValueElement in ValueRange)
            {
                    dynamic el = Convert.ChangeType(ValueElement, TypeOfValue);
                    DynamicList.Add(el);
            }

        }
        else //retrun empty List but with right type
        {
            Type d1 = typeof(List<>);

            Type[] typeArgs = { CallingType };

            Type DynamicListType = d1.MakeGenericType(typeArgs);

            object DynamicListObj = Activator.CreateInstance(DynamicListType);

            DynamicList = Convert.ChangeType(DynamicListObj, DynamicListType);
        }

        return DynamicList;
    }

I think that I'll add also a try catch somewhere.

how to test

                if (PropertyType == typeof(UInt32))
                {
                    List<UInt32> UInt32_test = NewProperty.ConvertList(PropertyType);
                }
                if (PropertyType == typeof(string))
                {

                    List<string> string_test = NewProperty.ConvertList(PropertyType);
                }

Upvotes: -2

LukeH
LukeH

Reputation: 269388

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; });

Upvotes: 18

Stan R.
Stan R.

Reputation: 16065

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);
}

Upvotes: 4

Jon
Jon

Reputation: 2279

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);

Upvotes: 1

Svante Svenson
Svante Svenson

Reputation: 12478

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

Upvotes: 0

TLiebe
TLiebe

Reputation: 7986

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() );
        }

Upvotes: 0

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