List with int array - accessing the array

Question

I have a class (students) with say 2 strings and an int array

A second class then does this:

List<student> myS = new List<student>();

All of this works correctly and I have a list containing multiple students. I am however having difficulty accessing the values within the int[].

So, my student list is populated from a database and into a list.

I then have a generic class which has a parameter List which I then want as a data table. The generic class will be called for the student class, subjects class and other classes - some of which may contain arrays and some which do not.

If I debug and step through, I get the following: (() myS.stu[6].termMark[1] and the value is 50. However if I enter int d =stu[6].termMark[1] the error is T does not contain a definition for termMark and no extension method 'termMark' accepting a first argument of type T could be found.

int d = myS[0][1] returns the error

cannot apply indexing with [] to an expression of type 'T'

. I have tried various things like creating a separate list and adding it to myS. Nothing works.

Thanks in advance for the help.

I am fairly new to this and probably missing the obvious...

int d = myS[0].YourArrayFieldName[1] ; (The field must be public) — George Vovos
– George Vovos, Commented May 31, 2015 at 14:25
You have to use the property name to get the values from student object int d = myS[0].ArrayProperty[1] — Null Pointer
– Null Pointer, Commented May 31, 2015 at 14:26
student is not a 2 stage list so what is with the second index — Milad Qasemi
– Milad Qasemi, Commented May 31, 2015 at 14:26
I guess you have a generic function somewhere.Show us the entire example — George Vovos
– George Vovos, Commented May 31, 2015 at 14:29

George Vovos · Accepted Answer · 2015-05-31 14:46:27Z

1

You must read about Generic Constraints
You cannot do much with an argument of type T.
If your function accepts arguments of type student , add a constraint like this

private static void NewMethod<T>(List<T> myS) where T : student
{
        int d = myS[0].IntArray[1];
}

The following is not related your problem...
If you add an indexer to your class you can make it a little shorter

public class student
{
    public int[] IntArray;

    public int this[int x]
    {
        get
        {
            return IntArray[x];
        }
    }
}
private static void NewMethod<T>(List<T> myS) where T : student
{
        int d = myS[0][3];
 }

edited May 31, 2015 at 14:46

answered May 31, 2015 at 14:35

George Vovos

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Comments

Afzaal Ahmad Zeeshan · Accepted Answer · 2015-05-31 14:28:24Z

0

Perhaps the type T does not hold any definition for indexers. But, your field (int[]) does. So, instead of calling the indexer upon your object (student) call it on the field of it. So, for this answer I would assume that your object is declared as class like this

public class student {
   public string S { get; set; }
   public string s { get; set; }
   public int[] integers { get; set; }
}

Now, you can indeed call the indexers on the integers field but not on the student object itself (it does not have any indexing mechanism). Such as,

int d = myS[0].integers[1]; // <-- your code should be

The above code (if compiled) would give you the element at the index 1 (2nd element) of the first object in the list. You were instead calling the element at index 1 of the student (which does not have indexers?).

answered May 31, 2015 at 14:28

Afzaal Ahmad Zeeshan

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1 Comment

George Vovos Over a year ago

myS[0] is obviously of type T that's why he gets that error.Even if he add an indexer in his class he will still get that error...

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