How to add array of objects to List in c#

Question

Let me explain I have a class X

public class X
{
  private List<Y> y;
}

I have another class Y

public class Y
{
  int a ;
  Private List<Z> z;
}

Now i want to mannually assign some values to class Y object whitch is an array of obejcts of size 2. Now i have added the values. How can i add this to the object of class X, in which a propery of type List of Class Y exists. Hope am able to explain it correctly.

i have

Y [] y1= new Y[2];
y1[0] = new Y();
y1[0].a=1;
y1[1]=new Y();
y1[0].a=2;

How can i assign y1[0] and y1[1] to object of X.

X x1=new X();
x1.y.add(y1[0]);
x1.y.add(y1[1]);

Its failing...

Please help me .

Please define "Its Failing". Are you getting any object null reference error? If so, in `class X` constructor, create a new list like `y = new List()`. — Sandy, Aug 14 '13 at 06:50
When you do `X x1=new X();` then your `x.Y` is actually `null`, so do `x1.y = new List();` — Rumplin, Aug 14 '13 at 06:51
You defined the List as field, not as property. http://stackoverflow.com/questions/295104/what-is-the-difference-between-a-field-and-a-property-in-c — Jeroen van Langen, Aug 14 '13 at 06:57
Object reference not set to an instance of an object is the error am getting. Now i have initialized a per the comments. — Anjana, Aug 14 '13 at 07:02

Sayse · Answer 1 · 2013-08-14T07:05:33.287

you can use AddRange

x1.y.AddRange(y1);
x1.y.AddRange(y1.GetRange(0,2)); // Adds first two elements

Although if its only a couple elements, its probably just as efficient to add them on their own

Since your list is private you may wish to add a method to do this

public void AddRangeToList(List<Y> items)
{
     y.AddRange(items);
}
x.AddRangeToList(y1);
x.AddRangeToList(y1.GetRange(0,2));

It appears you never initialise your arrays I would make constructors to do this

public X()
{
    y = new List<Y>();
}

public Y()
{
     z = new List<Z>();
}

Damith · Answer 2 · 2013-08-14T07:01:49.687

1

if you want to access properties of the class you need to make them public

X x1=new X();
x1.y = new List<Y>(); // need create instant of y before add items 
x1.y.Add(y1[0]);
x1.y.Add(y1[1]);

I would change the classes as below

public class X
{
    public List<Y> y { get; set; }
}


public class Y
{
    public int a;
    public List<Z> z { get; set; }
}

edited Aug 14 '13 at 07:01

answered Aug 14 '13 at 06:49

Damith

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`x1.y = new List();` will initialize – Damith Aug 14 '13 at 07:08
@ Damith Eventhough i have updated as you suggested. Its throwing the error "Object reference not set to an instance of an object." This is thrown when we try to add ie, x1.y.add(y[0]); where y forms an array of Objects of Type y. – Anjana Aug 14 '13 at 07:21
have you added `x1.y = new List()` line before that? – Damith Aug 14 '13 at 07:26
@Damith yes i have added. For your info Y[0] and y[1] belongs to array of object of type Y only. – Anjana Aug 14 '13 at 07:47
I would not create a read/write property of type List< >, i would use a IEnumerable< > instead for read/write properties. – Jeroen van Langen Aug 14 '13 at 07:56

Jeroen van Langen · Answer 3 · 2013-08-14T07:51:50.957

You should make your list property public instead of private.

Accessibility Levels (C# Reference) http://msdn.microsoft.com/en-us/library/ba0a1yw2.aspx

-

I would create a constructor that creates an instance of the List< Y>.

classes:

    public class X
    {
        public X()
        {
            Y = new List<Y>();
        }

        public List<Y> Y { get; private set; }
    }

    public class Y
    {
        public Y()
        {
            Z = new List<Z>();
        }

        public int A { get; set; }
        public List<Z> Z { get; private set; }
    }

    public class Z
    {
        public int V { get; set; }
    }

Usage:

        Y[] y1 = new Y[2];
        y1[0] = new Y();
        y1[0].A = 1;
        y1[1] = new Y();
        y1[1].A = 2;

        X x1 = new X();
        x1.Y.Add(y1[0]);
        x1.Y.Add(y1[1]);

        // or
        X x2 = new X();
        x2.Y.AddRange(y1);

        // or
        X x3 = new X();
        foreach (Y y in y1)
            x3.Y.Add(y);

If you specified the error, i could tell what went wrong. I updated it, It's still the same code, tell me where it differs/went wrong? note: i would not name my properties the same as classes. — Jeroen van Langen, Aug 14 '13 at 08:03

How to add array of objects to List in c#

3 Answers3