Dear All

this is my first post in this forum

i have an issue i am trying to solve it since about 3 monthes

I got a type in a Type variable

Type T ;

I have a List of objects

List<Object> mList ;

i want to case mList as a List<T>

is there any solution ?

THanks in advance

Hi,

To cast two lists use this static class:

public class ListConverter<TFrom, TTo>
    where TFrom : TTo
    {
        public static IEnumerable<TTo> Convert(IEnumerable<TFrom> from)
        { return Convert(new List<TFrom>(from)); }
        public static List<TTo> Convert(List<TFrom> from)
        { return from.ConvertAll<TTo>(new Converter<TFrom, TTo>(Convert)); }

        public static TTo Convert(TFrom from) { return (TTo)from; }
    }

And to use it:

private List<AttachedItem> GetAttachedFiles(int issueEventID)
        {
            return ListConverter<AttachedFile, AttachedItem>.Convert(attachedFileDAL.GetEventAttachedFiles(issueEventID));
        }

        private List<AttachedItem> GetDispatches(int issueEventID)
        {
            return ListConverter<Dispatch, AttachedItem>.Convert(dispatchDAL.GetDispatches(issueEventID));
        }

Here AttachedFile and Dispatch inherits from AttachedItem.

 Dear

Thanks for your reply

unfortunatily there is 2 problems

1- your clas does not accept object as first type

2- your class does not accpt type variable as second type

here is example of the code i want to run

<object> lo = new List<object>();

lo.add(new Rectangle ( 0 , 0 , 50 , 50 ));

lo.add(new Rectangle ( 0 , 0 , 50 , 50 ));

Type T = typeof ( Rectangle) ;

ListConverter < object , T>.Convert ( lo );

If the objects you add to your "lo" really is of type Rectangle, the easiest way is to just cast them. With Linq you can do this very easy:

private static void Test()
{
    List<object> lo = new List<object>();
    lo.Add(new Rectangle(1, 0, 50, 50));
    lo.Add(new Rectangle(2, 0, 50, 50));
    List<Rectangle> converted = lo.Cast<Rectangle>().ToList();
}

 Rectangle is just an example

Actually i dont have a defind type like rectangle

I have the destination type stored in a type variable

Consider this code

void ProcessTTypeList( List<Object> T , Type mType )

{

 lo.add(new Rectangle ( 0 , 0 , 50 , 50 ));

lo.add(new Rectangle ( 0 , 0 , 50 , 50 ));

ListConverter < object , mType>.Convert ( lo ); /* this is what i rally need */

}

Well, I don't think that's possible. Probably the best thing to do is to change the way you think. Maybe you are trying to solve the wrong problem.

Why do you use a List<object>, and what do you want to do with the converted list?

You could also try the Dot Net forum at:

  http://forums.microsoft.com/MSDN/default.aspx?ForumGroupID=12&SiteID=1

TATWORTH, you don't link to a specific forum thread, and I don't know why that forum should be better than this. What we need to know to help is more about what the OP wants to achieve.

Maybe the best thing would be to use an interface for the types that could possibly be in the list.

anders__f:

TATWORTH, you don't link to a specific forum thread, and I don't know why that forum should be better than this

Whilst this is a very good forum for ASP.NET questions, there are certain questions which while they can be legitimatly asked on this forum, they could also be asked elsewhere. The MSDN Dot Net forum seemed the best other forum for the question to be asked.

anders__f:

Maybe the best thing would be to use an interface for the types that could possibly be in the list.

Good point! May I respectfully suggest that you either find an example elsewhere on the web or post a sample yourself.

I'm sure that there is a number of forums where this question could be asked, some of them maybe better suited than this forum. But my point is that in this thread on this forum I've already started to help, and there is definitely a number of other users on this forum that would be able to answer this question too.

The thing is, to be able to help the OP, we need some more description about the problem and what he wants to achieve. Sorry, but I can't see the point in trying another forum in this situation.

Anyway, here is a simple sample code showing how you could use an interface for the types that is to be added to the list. To use the methods or properties defined in the interface there is no need to cast the list.

using System;
using System.Collections.Generic;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            Rectangles();
            Circles();
            BothRectanglesAndCircles();
        }

        private static void Rectangles()
        {
            var list = new List<IGeometrical>
                           {
                               new Rectangle(0, 0, 50, 50),
                               new Rectangle(10, 10, 40, 40)
                           };
            DisplayArea(list);
        }

        private static void Circles()
        {
            var list = new List<IGeometrical>
                           {
                               new Circle(0, 0, 15),
                               new Circle(15, 15, 15)
                           };
            DisplayArea(list);
        }

        private static void BothRectanglesAndCircles()
        {
            var list = new List<IGeometrical>
                           {
                               new Rectangle(20, 20, 30, 10),
                               new Circle(15, 15, 45)
                           };
            DisplayArea(list);
        }

        private static void DisplayArea(List<IGeometrical> list)
        {
            foreach (var geometrical in list)
            {
                Console.WriteLine("{0}: {1}",
                    geometrical.Name,
                    geometrical.GetArea());
            }
        }
    }

    public interface IGeometrical
    {
        string Name { get; }
        double GetArea();
    }

    public class Rectangle : IGeometrical
    {
        public int X { get; set; }
        public int Y { get; set; }
        public int Width { get; set; }
        public int Height { get; set; }

        public Rectangle(int x, int y, int width, int height)
        {
            X = x;
            Y = y;
            Width = width;
            Height = height;
        }

        public string Name
        {
            get { return "Rectangle"; }
        }

        public double GetArea()
        {
            return Width * Height;
        }
    }

    public class Circle : IGeometrical
    {
        public int X { get; set; }
        public int Y { get; set; }
        public int Radius { get; set; }

        public Circle(int x, int y, int radius)
        {
            X = x;
            Y = y;
            Radius = radius;
        }

        public string Name
        {
            get { return "Circle"; }
        }

        public double GetArea()
        {
            return Math.PI * Radius * Radius;
        }
    }
}