changing data of class list

Question

I try to add new record to my list and change data of it, but it's change all record of array, here is my class and code:

The class:

 public class TransportDto
{
        public int type { get; set; }
        public string url { get; set; }
        public int Relationship { get; set; }
}

loading data to my list:

IQueryable<TransportDto> list = _entities.Database.SqlQuery<TransportDto>(filterExpression).AsQueryable();


List<TransportDto> lst = list.ToList();
TransportDto help =lst[1];// adding record like one of my result
lst.Add(help);

Now I try to change value of lst[lst.Count-1] but when I change it , lst[1] change too

lst[lst.Count-1].type=3;

on result both lst[lst.Count-1] and lst[1] changes to 3, but I just try to change one record of array

this usually happens when two values in the list are pointing to the same object — Neville Nazerane, Sep 09 '17 at 04:28
@NevilleNazerane am I doing wrong, how should I provide it ? — sarzin, Sep 09 '17 at 04:29
i posted an answer of how you can provide it below. The above comment is for general reference. Any time you notice that changing an object also changes another object, most of the time it is because they are pointing to the same object — Neville Nazerane, Sep 09 '17 at 04:41

score 1 · Accepted Answer · answered Sep 09 '17 at 04:38

When you write TransportDto help =lst[1];, you are getting the object at the index of 1. When you add this object to the list, you are adding the same object to the list not a copy of it. Which means in the list, the indices of 1 and lst.Count-1 point to the same object. When you access the object as lst[lst.Count-1] you are accessing this object and .type=3 makes changes to the object the two indices are pointing to.

If you want a copy of the object in lst[1], consider cloning the object. This could make a copy of the object. You can refer here: How to Clone Objects

To simplify, in your case you can create a clone function like this:

public class TransportDto
{
    public int type { get; set; }
    public string url { get; set; }
    public int Relationship { get; set; }

    public TransportDto Clone(){
        return new TransportDto{
            type = type,
            url = url,
            Relationship = Relationship
        };
    }
}

This clone function creates a new object of TransportDto and passes the same values thus creating a copy. Now in your list you can do this:

TransportDto help =lst[1].Clone();

Now help stores a copy of lst[1].

changing data of class list

1 Answers1