Selecting DataGridView Rows Programatically

Hi I have some code in my datagridview's CellMouseDown event to select multiple rows.

It takes back my selection, after doing multiple selections over 1 time. How can I fix this? Note: I don't want to use mouseup event because it will make things worse imo.

Here's my code:

VB.NET Code:

private void SelectDgvItems(bool ClearRequest)
{
    // Check if there's a line
    if (programs_dgv.RowCount <= 0)
    {
        return;
    }
 
    // Sort by name
    programs_dgv.Sort(programs_dgv.Columns[2], ListSortDirection.Ascending);
 
    // Select required rows and set scrolling position
    if (SelectedIndexes != null)
    {
        if (ClearRequest == true)
        {
            programs_dgv.ClearSelection();
        }
 
        for (int i = 0; i <= SelectedIndexes.Count() - 1; i++)
        {
            programs_dgv[1, SelectedIndexes[i]].Selected = true;
        }
    }
 
    MessageBox.Show(LastSelectedIndex.ToString());
}
 
private void programs_dgv_CellContentClick(object sender, DataGridViewCellEventArgs e)
{
    programs_dgv.CommitEdit(DataGridViewDataErrorContexts.Commit);
}
 
private void programs_dgv_CellMouseDown(object sender, DataGridViewCellMouseEventArgs e)
{
    CurrentRowIndex = e.RowIndex;
 
    Console.WriteLine(LastSelectedIndex.ToString() + "    " + CurrentRowIndex.ToString());
 
    // Check if there's a line
    if (programs_dgv.Rows == null)
    {
        return;
    }
 
    SelectedIndexes.Clear();
    SelectedIndexes = null;
    SelectedIndexes = new List<int>();
 
    // Reset SelectedIndexes
    for (int i = 0; i <= programs_dgv.RowCount - 1; i++)
    {
        if (programs_dgv.Rows[i].Selected == true)
        {
            SelectedIndexes.Add(i);
        }
    }
 
    // When shift+click
    if (e.Button == MouseButtons.Left && (ModifierKeys & Keys.Shift) == Keys.Shift)
    {
        if (CurrentRowIndex >= 0)
        {
            SelectedIndexes.Clear();
            SelectedIndexes = null;
            SelectedIndexes = new List<int>();
 
            // Set SelectedIndexes
            for (int i = LastSelectedIndex; i <= CurrentRowIndex; i++)
            {
                SelectedIndexes.Add(i);
                Console.WriteLine(SelectedIndexes[i].ToString() + Environment.NewLine);
            }
 
            // Select dgv items (ClearRequest = false)
            SelectDgvItems(false);
            return;
        }
 
        SelectDgvItems(false);
        return;
    }
 
 
 
    // When ctrl is not pressed
    if (e.Button == MouseButtons.Left && (ModifierKeys & Keys.None) == Keys.None)
    {
 
        SelectedIndexes.Clear();
        SelectedIndexes = null;
        SelectedIndexes = new List<int>
        {
            CurrentRowIndex
        };
 
        // Set dgv items (ClearRequest = true)
        SelectDgvItems(true);
 
        return;
    }
 
 
 
    // right click
    if (e.Button == MouseButtons.Right)
    {
        // Open context menu
        int currentMouseOverRow = programs_dgv.HitTest(e.X, e.Y).RowIndex;
 
        if (currentMouseOverRow >= 0)
        {
            Cms_DatagridView.Items[0].Text = "düzenle (" + SelectedIndexes.Count().ToString() + ")";
        }
 
        Cms_DatagridView.Show(programs_dgv, programs_dgv.PointToClient(System.Windows.Forms.Control.MousePosition));
 
        // -----------------------------------------------------------------------------
 
        // If current row isn't selected add it to the list
        if (programs_dgv.Rows[CurrentRowIndex].Selected == false)
        {
            SelectedIndexes.Add(CurrentRowIndex);
        }
 
        SelectedIndexes.Clear();
        SelectedIndexes = null;
        SelectedIndexes = new List<int>
            {
                CurrentRowIndex
            };
 
        SelectDgvItems(true);
 
        LastSelectedIndex = CurrentRowIndex;
        return;
    }
 
}

Perhaps start with a FULL and CLEAR explanation of exactly what you expect the code to do, exactly what it does do and where exactly in the code your debugging told you that the behaviour deviated from your expectation.

Hi, thanks for the reply any warning. I need rows of dgv to be selected programmatically. For example if run the code above,

1. Open the program, row: 0 is selected by default
2. I select multiple rows with shift+click (starting from row 0), this works well (my code only supports up to down selections yet).
3. I do shift+click on another row to expand the selection (I expect start index to be 0)
4. I'm not getting any errors
4b. It clears my selection and applies 3rd action's start index, not 0.

How can I fix it to make multiple selections without losing start index 0, or a start index created by single clicking but not shift+click?

I get:

Attachment 159973

I expect:
Attachment 159975