CODEWITHSUNDEEP
c#listgenericsdelegatesfind
Pacane
Pacane

Reputation: 21481

C# - using List<T>.Find() with custom objects

I'm trying to use a List<T> with a custom class of mine, and being able to use methods like Contains(), Find(), etc., on the list. I thought I'd just have to overload the operator == but apparently, one way of doing that is to use a delegate method with the Find()...

Note: Right now, I've overloaded the Equals() method to get the Contains() method to work, but I still couldn't get the Find() function to work.

What would be the best way of getting both to work?

I'm using the latest C# /.NET framework version with mono, on linux.

edit: Here's my code

using System;
namespace GuerreDesClans
{
public class Reponse : IEquatable<Reponse>
{
    public Reponse ()
    {
        m_statement = string.Empty;
        m_pointage = 0;
    }

    public Reponse (string statement, int pointage)
    {
        m_pointage = pointage;
        m_statement = statement;
    }


    /*
     * attributs privés
     */

    private string m_statement;
    private int m_pointage;


    /*
     * properties
     */

    public string Statement {
        get { return m_statement; }
        set { m_statement = value; }
    }

    public int Pointage {
        get { return m_pointage; }
        set { m_pointage = value; }
    }

    /*
     * Equatable
     */

    public bool Equals (Reponse other)
    {
        if (this.m_statement == other.m_statement)
            return true;
        else
            return false;
    }
}

}

and how I would like to search my Reponse objects using the find() function...

list.find("statement1"); // would return a Reponse object

Upvotes: 47

Views: 211079

Answers (5)

Junaid Pathan
Junaid Pathan

Reputation: 4316

It's easy, just use list.Find(x => x.name == "stringNameOfObjectToFind");

Upvotes: 0

Xavier Poinas
Xavier Poinas

Reputation: 19733

Find() will find the element that matches the predicate that you pass as a parameter, so it is not related to Equals() or the == operator.

var element = myList.Find(e => [some condition on e]);

In this case, I have used a lambda expression as a predicate. You might want to read on this. In the case of Find(), your expression should take an element and return a bool.

In your case, that would be:

var reponse = list.Find(r => r.Statement == "statement1")

And to answer the question in the comments, this is the equivalent in .NET 2.0, before lambda expressions were introduced:

var response = list.Find(delegate (Response r) {
    return r.Statement == "statement1";
});

Upvotes: 75

Shimon Doodkin
Shimon Doodkin

Reputation: 4569

http://msdn.microsoft.com/en-us/library/x0b5b5bc.aspx

        // Find a book by its ID.
        Book result = Books.Find(
        delegate(Book bk)
        {
            return bk.ID == IDtoFind;
        }
        );
        if (result != null)
        {
            DisplayResult(result, "Find by ID: " + IDtoFind);   
        }
        else
        {
            Console.WriteLine("\nNot found: {0}", IDtoFind);
        }

Upvotes: 0

phoog
phoog

Reputation: 43046

Previous answers don't account for the fact that you've overloaded the equals operator and are using that to test for the sought element. In that case, your code would look like this:

list.Find(x => x == objectToFind);

Or, if you don't like lambda syntax, and have overriden object.Equals(object) or have implemented IEquatable<T>, you could do this:

list.Find(objectToFind.Equals);

Upvotes: 8

Greg Sansom
Greg Sansom

Reputation: 20840

You can use find with a Predicate as follows:

list.Find(x => x.Id == IdToFind);

This will return the first object in the list which meets the conditions defined by the predicate (ie in my example I am looking for an object with an ID).

Upvotes: 47

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