Foreach loop doesn't finish in c# with List<>

Question

I know it's very strange but I don't find another way to say it. Please see the image below count list

enter image description here

The output is 1 and always it's the same!

I really don't understand what happend here. Can anyone explain to me?

What is the type of `Mediciones`? Why do you think the foreach loop doesn't finish? Use the debugger to step through the execution of the loop. In particular, see if the `if` condition triggers in each loop iteration. — Michael Petrotta, Mar 02 '13 at 02:56
output to the console a statement like "Loop Ended" at the end of the loop. That's the easiest way to test whether the loop ends or not. — Nabou, Mar 02 '13 at 03:03
Can you try moving i += 1; Console.WriteLine(i); outside the if to see how many times it loops? — Divi, Mar 02 '13 at 06:12

chue x · Accepted Answer · 2013-03-02T15:38:50.423

Just a couple of observations on your Modelo and Medicion classes:

public class Modelo<T>
{
    // 1) note PROTECTED set on Id
    public virtual int Id { get; protected set; }

    public override bool Equals(object obj)
    {
        ...
        // 2) comparison is based on Id
        return (this == obj || this.Id == specificOject.Id);
    }
    ...
}

public class Medicion : Modelo<Medicion> {...}

The Id member is defined as protected set.
The Equals method defines two objects as the same if the Id in both are the same.

Are you setting the Id of your Medicion objects anywhere? If not, they are likely to all be 0. If all the Ids are the same, this makes all your objects look the same (your equality definition is based on Id).

Therefore, Mediciones.Contains will always be true after the first object is added. You don't provide any info on Mediciones, but I am assuming here that it is a standard List with no overrides.

score 0 · Answer 2 · answered Mar 02 '13 at 02:51

0

One of those intellisense dialogs is showing you TodasMediciones. The other is showing you Mediciones. These are not the same value.

answered Mar 02 '13 at 02:51

SecurityMatt

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score 0 · Answer 3 · edited May 23 '17 at 10:32

0

See Modify List.Contains behavior

You're going to want to implement IEquatable<T> in your Medicion.

edited May 23 '17 at 10:32

Community

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1

answered Mar 02 '13 at 02:56

Dustin Kingen

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Good call, but you'd think the default implementation would use a reference comparison, and therefore trigger the `if` condition all four times through the loop, for each of the four different objects in the list. – Michael Petrotta Mar 02 '13 at 03:01
@MichaelPetrotta I'm pretty sure the default `List` behavior when you `Add` an object is to copy it. – Dustin Kingen Mar 02 '13 at 03:03
Well, copy the reference to the object. It doesn't do a deep copy. There are four objects he's adding from `TodasMediciones` to `Mediciones`. I'd think that the `Contains` would return false for each new item. – Michael Petrotta Mar 02 '13 at 03:11

score 0 · Answer 4 · answered Mar 02 '13 at 02:57

0

I don't understand what is your problem. The loop loops on TodasMediciones which is a List. The second debugger is on Mediciones. Both are different objects.

answered Mar 02 '13 at 02:57

Nikhil Agrawal

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The second image just shows that the `Mediciones` isn't the same values than `TodasMediciones` – Cristhian Boujon Mar 02 '13 at 03:16

score 0 · Answer 5 · answered Mar 02 '13 at 13:08

Well I'm wrong. The problem (I don't know why) is !Mediciones.Contains(m). The first time is false and in the next iterations is true. I change method as follow

public virtual void AddMediciones(List<Medicion> TodasMediciones)
        {
            int i = 0;
            foreach (Medicion m in TodasMediciones)
            {
                Console.WriteLine(Mediciones.Contains(m));
                Console.WriteLine(m.Valor);
                Console.WriteLine("-------------------------------------------");
                if (!Mediciones.Contains(m))
                {
                    Mediciones.Add(m);
                }
            }
        }

Their output is:

False
1
-------------------------------------------
True
2
-------------------------------------------
True
3
-------------------------------------------
True
4
-------------------------------------------

Here is the Medicion definition:

public class Medicion : Modelo<Medicion>
    {
        public virtual DateTime Fecha { get; set; }
        public virtual decimal Valor { get; set; }
        public virtual Indicador Indicador { get; set; }
    }
}

And their parent definition

public class Modelo<T>
{
    public virtual int Id { get; protected set; }

    public override bool Equals(object obj)
    {
        if (obj == null || obj.GetType() != this.GetType())
        {
            return false;
        }

        Modelo<T> specificOject = (Modelo<T>)obj;
        return (this == obj || this.Id == specificOject.Id);
    }

    public override int GetHashCode()
    {
        return Id.GetHashCode() ^ 5;
    }
}

Foreach loop doesn't finish in c# with List<>

5 Answers5