ListBox.DataSource doesn't show data on the list

Question

Help guys, I have a List of Points List points = new List(); , what I'm trying to do is removing some data from the list. I used a listbox to see whether it works. This is my code:

        points.Add(new PointF(50, 100));
        points.Add(new PointF(50, 100));
        points.Add(new PointF(200, 300));
        points.Add(new PointF(100, 200 ));
        points.Add(new PointF(50, 100));
        points.Add(new PointF(100, 200));
        points.Add(new PointF(200, 300));
        points.Add(new PointF(100, 200));
        points.Add(new PointF(200, 300));

        listBox1.DataSource = points;

        float[] sumofxandy = new float[points.Count()];
        for (int x = 0; x < points.Count(); x++)
        {
            sumofxandy[x] = points.ElementAt(x).X + points.ElementAt(x).Y;
        }


        //code that removes data from list starts from here
        float[] difference = new float[points.Count()]; //there is something wrong with this and I don't know what. It has no error but it doesn't make my list to be shown in the listbox.
        for (int i = 0; i <= points.Count(); i++) 
        {
            for (int j = 1; j <= points.Count(); j++) 
            {

                difference[j] = sumofxandy[i] - sumofxandy[j];
                if (difference[i] == 0) 
                {
                    points.RemoveAt(j);

                    MessageBox.Show("removed");
                }

            }
        } // ends here

        listBox2.DataSource = points;

When I erased the code that removes data from the list, the elements inside the list will be shown in the listbox. Help guys

Answer 1

Could it be that you are using the wrong variable in the if(difference[i] == 0) ?

When using your solution I get an ArgumentOutOfRangeException on the line points.RemoveAt(j);

difference[j] = sumofxandy[i] - sumofxandy[j];
if (difference[i] == 0) 
{
    points.RemoveAt(j);
     MessageBox.Show("removed");
}

When the line if(difference[i] == 0) are changed to:

if(difference[j] == 0) 

then the code executes successful, with 3 items in listbox2.

EDIT:

As @wdosanjos mentions, you should do your loops with a < rather than <= since you start counting at zero, and not 1. The last element is really at position Count - 1, since the list are zero indexed.

EDIT:

When I changed the loops to: (notice the change in <= to < , it does not throw an exception.)

for (int i = 0; i < points.Count(); i++)
        {
            for (int j = 1; j < points.Count(); j++)
            {

                difference[j] = sumofxandy[i] - sumofxandy[j];
                if (difference[i] == 0)
                {
                    points.RemoveAt(j);

                    MessageBox.Show("removed");
                 }

            }
        } // ends here

This returns two elements.

Answer 2

Try changing your for loops as follows (from <= to < ). I think you are getting a hidden IndexOutOfBoundsException .

for (int i = 0; i < points.Count(); i++) 
{
    for (int j = 1; j < points.Count(); j++) 

Answer 3

Notice that you are modifying the very same list you are iterating over. This may just as easy remove all the points. You should better create a new list for points that should be removed:

    //code that removes data from list starts from here
    List<PointF> pointsToRemove = new List<PointF>();
    float[] difference = new float[points.Count()];
    for (int i = 0; i <= points.Count(); i++) 
    {
        for (int j = 1; j <= points.Count(); j++) 
        {

            difference[j] = sumofxandy[i] - sumofxandy[j];
            if (difference[i] != 0) 
            {
                pointsToRemove.Add(points[j]);

                MessageBox.Show("removed");
            }

        }
    }

    listBox2.DataSource = points.Except(pointsToRemove).ToList();