How to copy one element of a Generic Collection?

Question

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

 

private List<CalculationResult> cantileverResults = new List<CalculationResult>();
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?

Liutauras Medziunas · 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); } } If it was helpful please rate it.

Liutauras Medziunas · Answer

Hi Suthish Thank you.

Suthish Nair · Answer

HI Liutauras Good sample..

Javier · Answer

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 Medziunas · Answer

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.