How can I get the count of the visible rows of a grid?

Question

We have this obstacle in populating data. Let's say I have 11 tests and every test has two targets. The code populates data into a DevExpress data grid in WPF . So I have 11 tests but only 5 are visible (we scroll to see the rest):

I am trying to accomplish something similar to this:

    on first   VISIBLE row [Test1][Target1]
    on second  VISIBLE row [Test2][Target1]
    ..
    on last    VISIBLE row [Testn][Target1]

    next column

    on first   VISIBLE row [Test1][Target2]
    on second  VISIBLE row [Test2][Target2]
    ..
    on last    VISIBLE row [Testn][Target2]

The current code is an event handler from the grid and it works but with erros. It gets called exactly as much as visible rows count (!!) however I couldn't find how to control that. The code is causing problems (duplicating data sometimes and flipping data between columns sometimes). Commented is what I really want. I need to incremenet target index which is unboudSampleDrawIndex once I reach the last visible row. Please help

private void testGrid_CustomUnboundColumnData(object sender, GridColumnDataEventArgs e)
{
    if (e.IsGetData)
    {
        Test currentTest = ((GalleryViewModel)DataContext).CurrentTests.ElementAtOrDefault(e.ListSourceRowIndex);
        unboundSampleDrawIndex = 0; // starts from target zero

        if (currentTest != null)
        {
            if ((int)e.Column.Tag < currentTest.Samples.Count && unboundSampleDrawIndex <= currentTest.Samples.Count - 1)
            {
                if (currentTest.IsReference)
                    e.Value = currentTest.Samples.ElementAt(unboundSampleDrawIndex).ABC; // here I am taking target 0 for the first column, until incremented
                else
                    e.Value = currentTest.Samples.ElementAt(unboundSampleDrawIndex).Delta; // here I am taking target 0 for the first column, until incremented
            }
            else
                e.Value = "";

            if (unboundSampleDrawIndex >= ??? ) //here I want to know it reached the last visible row
                unboundSampleDrawIndex++; // incremenet to populate next target
        }
    }
}

Answer 1

This fixed the issue. By generating a tag for every column and then setting it as the index in the target vectors.

    private void testGrid_CustomUnboundColumnData(object sender, GridColumnDataEventArgs e)
    {

        if (e.IsGetData)
        {
            Test currentTest = ((GalleryViewModel)DataContext).CurrentTests.ElementAtOrDefault(e.ListSourceRowIndex);

            if (currentTest != null)
            {
                if ((int)e.Column.Tag < currentTest.Samples.Count && unboundSampleDrawIndex <= currentTest.Samples.Count - 1)
                {
                    if (currentTest.IsReference)
                    {
                        e.Value = currentTest.Samples.ElementAt((int)e.Column.Tag).ABC;
                    }

                    else
                    {
                        e.Value = currentTest.Samples.ElementAt((int)e.Column.Tag).Delta;
                    }

                    unboundSampleDrawIndex++;
                }

                else
                {
                    e.Value = "";
                }

                if (unboundSampleDrawIndex >= currentTest.Samples.Count)
                {
                    unboundSampleDrawIndex = 0;
                }
            }
        }
    }