Update an item from a generic list to a specific item

Question

How do I update a specific element of a generic list by locating by ID and passing an updated object in its place, updating the name and email?

class Program
{
    static void Main(string[] args)
    {
        List<Aluno> aluno = new List<Aluno>{
            new Aluno() { AlunoId = 1, Nome = "Cláudia",Email="[email protected]" },
            new Aluno() { AlunoId = 2, Nome = "Pedro",Email="[email protected]" },
            new Aluno() { AlunoId = 3, Nome = "Eduardo",Email="[email protected]" }
        };

        Console.WriteLine("==================================");

        foreach (var item in aluno)
        {
            Console.WriteLine("ID: {0}\nNome: {1}\nEmail: {2}", item.AlunoId, item.Nome,item.Email);
            Console.WriteLine("==================================");
        }

        Console.WriteLine("\nLista Atualizada\n");

        int iElemento = 1;

        var elem = aluno.Where<Aluno>(a => a.AlunoId == iElemento).FirstOrDefault();
        int index = aluno.IndexOf(elem);

        aluno[index].Nome = "Cláudia Limeira";
        aluno[index].Email = "[email protected]";

        foreach (var item in aluno)
        {
            Console.WriteLine("ID: {0}\nNome: {1}\nEmail: {2}", item.AlunoId, item.Nome, item.Email);
            Console.WriteLine("==================================");
        }

        Console.Read();
    }
}

class Aluno
{
    public int AlunoId { get; set; }
    public string Nome { get; set; }
    public string Email { get; set; }
}

Answer 1

I remade the code giving a more general solution, I believe you can take what you don’t need:

using static System.Console;
using System.Collections.Generic;
using System.Linq;
                    
public class Program {
    public static void Main(string[] args) {
        var alunos = new List<Aluno> {
            new Aluno() { AlunoId = 1, Nome = "Cláudia", Email = "[email protected]" },
            new Aluno() { AlunoId = 2, Nome = "Pedro",   Email = "[email protected]" },
            new Aluno() { AlunoId = 3, Nome = "Eduardo", Email = "[email protected]" }
        };
        ImprimeAlunos(alunos);
        while (true) {
            var id = 0;
            Write("Qual ID de aluno deseja modificar? (-1 para encerrar)");
            if (int.TryParse(ReadLine(), out id)) {
                if (id == -1) break;
                var alunoAchado = alunos.FirstOrDefault(x => x.AlunoId == id);
                if (alunoAchado != null) {
                    Write("Qual o novo nome? ");
                    alunoAchado.Nome = ReadLine();
                    Write("Qual o novo e-mail? ");
                    alunoAchado.Email = ReadLine();
                } else WriteLine("Id inválido tente outro");
            } else WriteLine("Id inválido tente outro");
        }
         WriteLine("Nova Lista");
        ImprimeAlunos(alunos);
    }
    
    static void ImprimeAlunos(List<Aluno> alunos) {
        WriteLine("==================================");
        foreach (var item in alunos) {
            WriteLine($"ID: {item.AlunoId}\nNome: {item.Nome}\nEmail: {item.Email}");
            WriteLine("==================================");
        }
    }
}

class Aluno {
    public int AlunoId { get; set; }
    public string Nome { get; set; }
    public string Email { get; set; }
}

Behold working in the ideone. And in the .NET Fiddle. Also put on the Github for future reference.

Note that in case you are searching using LINQ the return is the item itself, so you do not need to use index to access it. What is changed in the found item will be reflected in the student list.

In its code the code uses the Where and the FisrtOrDefault. This is redundant since the second already does what the first one does in a way that is more appropriate to the context (the first tends to be slower). Then the code gets the item. The ideal is to change it and you preferred to find its index to change by the index as reported in the previous question. Except in this case, you don’t have to. Unless the problem requires you to do this, which I doubt, but then it would be better to solve it differently (by returning the index and not the item).

Note also that I used a more modern coding style. If you have any specific questions ask for clarification or open a question if you think the topic deserves.

You can improve even more, you can validate more things, but this is the basics.

I made another version without using LINQ. I mean, I did what LINQ would do.

Answer 2

To locate the item, you need to do:

var item = aluno.First(x => x.Id == 1); //Localizando o aluno com id 1

To update you:

item.Nome = "Novo nome";
item.Email = "[email protected]";

Like Aluno is a type by reference, when changing the object item, the object inside the List will also be updated.

Answer 3

You can create a crud to take care of the list :)/

like this ó

    private List<Obj> listaDeObjetos = new List<Obj>();

    public void Add(Obj obj)
    {
        listaDeObjetos.Add(obj);
    }

    public Obj Get(int id)
    {
        return listaDeObjetos.Find(c => c.Id == id);
    }

    public void Remove(Obj obj)
    {
        listaDeObjetos.Remove(obj);
    }

    public void Update(Cart objQueVaiSerAtualizado)
    {
        var objQueVaiSerRemovido= Get(objQueVaiSerAtualizado.Id);
        Remove(objQueVaiSerRemovido);
        Add(objQueVaiSerAtualizado);
    }

as to remove an object from a list it is necessary to pass the object, so the update becomes the most "complex" of the methods.

in the update method: you call it by passing the object that will be updated, say you changed the name, which is a property of the object and such, ai vc passes the obj with the new name, inside the method you search in the list using the Get method passing the id of the object that will be updated, the get method returns the object that is in the list and the name has not been changed, with this object you pass to the remove method, that will remove this outdated object in sequence calls the add to add the updated object.