How to copy one element of a Generic Collection?

Javier

I need to copy one element of a generic collection and add it to the list. Something similar to this:

 

private List cantileverResults = new List();
cantileverResults.Add(cantileverResults[previousIndex]);

The problem with this solution is that when I modify the new element, the previousIndex element changes as well. I believe this is because they are reference-type, not value-type. How can I just copy (clone?) the information from one element to another without affecting each other any further?

5 Replies

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Liutauras Medziunas15y ago
Accepted answer
You must use Clone() method.

class Program
    {
        public static void Main()
        {
            int previousIndex = 1;
            List cantileverResults = new List();

            cantileverResults.Add(new CalculationResult(20));
            cantileverResults.Add(new CalculationResult(30));
            cantileverResults.Add(new CalculationResult(40));

            cantileverResults.Add((CalculationResult)cantileverResults[previousIndex].Clone());

            Console.WriteLine("Before change");

            ShowResult(cantileverResults);

            cantileverResults[3].Amount = 100;

            Console.WriteLine("After change");

            ShowResult(cantileverResults);

            Console.ReadKey();
        }

        private static void ShowResult(List cantileverResults)
        {
            foreach (var result in cantileverResults)
            {
                Console.WriteLine(result);
            }
        }
    }

    public class CalculationResult : ICloneable
    {
        private decimal amount = 0;

        public decimal Amount
        {
            get { return this.amount; }
            set { this.amount = value; }
        }

        public CalculationResult(decimal amount)
        {
            this.amount = amount;
        }

        public object Clone()
        {
            return this.MemberwiseClone();      // call clone method
        }

        public override string ToString()
        {
            return String.Format("Amount: {0}", this.amount);
        }
    }

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Liutauras Medziunas15y ago
Hi Suthish,
Thank you.
Suthish Nair15y ago
HI Liutauras,
Good sample..
Javier15y ago
Thank you Liutauras. I implemented your idea but the result is the same: the new element and the element being copied are linked together and if you modify one the other is affected as well. I think in you example it works fine because 20, 30 and 40 are values, but in my case every element of the list is a reference-type. Please let me know if I'm wrong. Thank you.
Liutauras Medziunas15y ago
I wrote some code for you. You can use ICloneable interface. Just implement it in your CalculationResult class.

class Program
    {
        public static void Main()
        {
            int previousIndex = 1;
            List cantileverResults = new List();

            cantileverResults.Add(new CalculationResult(20));
            cantileverResults.Add(new CalculationResult(30));
            cantileverResults.Add(new CalculationResult(40));

            cantileverResults.Add(cantileverResults[previousIndex].Clone());

            foreach (var result in cantileverResults)
            {
                Console.WriteLine(result);
            }

            Console.ReadKey();
        }
    }

    public class CalculationResult : ICloneable
    {
        private decimal amount = 0;

        public CalculationResult(decimal amount)
        {
            this.amount = amount;
        }

        public object Clone()
        {
            return this.MemberwiseClone();      // call clone method
        }

        public override string ToString()
        {
            return String.Format("Amount: {0}", this.amount);
        }
    }

Please rate my post if it was helpful.