Exception when adding a new row to my DataGridView

Question

I have this issue. It starts like this:

I can double-click the drop arrow and pick a colour OK:

At this point, I can click the dropdown again and it is correctly selected:

The issue is when I want to add a new row. Even if I just go to click on the new row cell:

I then data an data error exception:

Thereafter the previous cell draws incorrectly:

I can't quite work out how to resolve this.

My code:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.Xml.Linq;
using Teigha.Core;
using Teigha.TD;

namespace Viewer
{
    public partial class Editor : Form
    {
        uint[] _CurPalette = Teigha.Core.AllPalettes.getDarkPalette();

        public Editor()
        {
            InitializeComponent();
        }

        private void Editor_Load(object sender, EventArgs e)
        {
            DataGridViewComboBoxColumn cboColumn = new DataGridViewComboBoxColumn();
            cboColumn.Name = "Color";

            List<ushort> listColors = new List<ushort>();
            listColors.Add(1);
            listColors.Add(2);
            listColors.Add(3);
            listColors.Add(4);
            listColors.Add(5);
            listColors.Add(6);
            listColors.Add(7);
            listColors.Add(8);
            listColors.Add(9);
            listColors.Add(250);
            listColors.Add(251);
            listColors.Add(252);
            listColors.Add(253);
            listColors.Add(254);
            listColors.Add(255);

            foreach (ushort iColorIndex in listColors)
            {
                using (OdCmColor oColor = new OdCmColor())
                {
                    oColor.setColorIndex(iColorIndex);
                    ComboboxColorItem oColorItem = new ComboboxColorItem(
                        oColor.colorNameForDisplay(),
                        iColorIndex,
                        Color.FromArgb(oColor.red(), oColor.green(), oColor.blue()));
                    cboColumn.Items.Add(oColorItem);
                }
            }

            this.DataGridView1.Columns.Add(cboColumn);
        }

        private void DataGridView1_EditingControlShowing(object sender, DataGridViewEditingControlShowingEventArgs e)
        {
            if (e.Control is ComboBox)
            {
                ComboBox theCB = (ComboBox)e.Control;
                theCB.DrawMode = DrawMode.OwnerDrawFixed;
                try
                {
                    theCB.DrawItem -= new DrawItemEventHandler(this.combobox1_DrawItem);
                }
                catch { }
                theCB.DrawItem += new DrawItemEventHandler(this.combobox1_DrawItem);
            }
        }

        private void combobox1_DrawItem(object sender, DrawItemEventArgs e)
        {
            Graphics g = e.Graphics;
            Color c = Color.Empty;
            string s = "";
            Brush br = SystemBrushes.WindowText;
            Brush brBack;
            Rectangle rDraw;
            bool bSelected = Convert.ToBoolean(e.State & DrawItemState.Selected);
            bool bValue = Convert.ToBoolean(e.State & DrawItemState.ComboBoxEdit);

            rDraw = e.Bounds;
            rDraw.Inflate(-1, -1);

            if (bSelected & !bValue)
            {
                brBack = Brushes.LightBlue;
                g.FillRectangle(Brushes.LightBlue, rDraw);
                g.DrawRectangle(Pens.Blue, rDraw);
            }
            else
            {
                brBack = Brushes.White;
                g.FillRectangle(brBack, e.Bounds);
            }

            try
            {
                //s = ((ComboBox)sender).Items[e.Index].ToString();
                ComboboxColorItem oColorItem = (ComboboxColorItem)((ComboBox)sender).Items[e.Index];
                s = oColorItem.ToString();
                c = oColorItem.Value;
            }
            catch
            {
                s = "red";
                c = Color.Red;
            }

            SolidBrush b = new SolidBrush(c);
            Rectangle r = new Rectangle(e.Bounds.Left + 5, e.Bounds.Top + 3, 10, 10);
            g.FillRectangle(b, r);
            g.DrawRectangle(Pens.Black, r);
            g.DrawString(s, Form.DefaultFont, Brushes.Black, e.Bounds.Left + 25, e.Bounds.Top + 1);

            b.Dispose();
            g.Dispose();
        }

        private void DataGridView1_DataError(object sender, DataGridViewDataErrorEventArgs e)
        {
            MessageBox.Show(e.Exception.ToString());
        }
    }

    public class ComboboxColorItem
    {
        public string Name { get; }
        public ushort Index { get; }
        public Color Value { get; }

        public ComboboxColorItem(string Name, ushort Index, Color Value)
        {
            this.Name = Name;
            this.Index = Index;
            this.Value = Value;
        }
        public override string ToString()
        {
            return Name;
        }
    }
}

Update:

If I put this code into the form load event:

this.DataGridView1.Rows.Add(new ComboboxColorItem("red", 1, Color.Red));

Then I immediately get the exception.

I tried adding a secondary default constructor and it made no difference:

public class ComboboxColorItem
{
    public string Name { get; set; }
    public ushort Index { get; set; }
    public Color Value { get; set; }

    public ComboboxColorItem()
    {
        this.Name = "red";
        this.Index = 1;
        this.Value = Color.Red;
    }
    public ComboboxColorItem(string Name, ushort Index, Color Value)
    {
        this.Name = Name;
        this.Index = Index;
        this.Value = Value;
    }
    public override string ToString()
    {
        return Name;
    }
}

I also tried adding this to the load event:

cboColumn.ValueType = typeof(ComboboxColorItem);

Didn't make a difference.

Update:

I have used the CellParsing answer and I seem to no longer gave crashes:

My only comment now is that I was hoping that the block of colour would remain visible in the cell. But I only see the block of colour when I click the drop arrow. Is this a separate question?

Answer 1

DataGridView has trouble with parsing the selected color item. I suggest that you apply custom parsing logic to that column:

DataGridView1.CellParsing += ColorCellParsing;

private void ColorCellParsing(object sender, DataGridViewCellParsingEventArgs e)
{
    var grid = (DataGridView)sender;
    var column = grid.Columns[e.ColumnIndex] as DataGridViewComboBoxColumn;
    if (column == null || column.Name != "Color")
        return;
    foreach (ComboboxColorItem item in column.Items)
    {
        if (item.Name == (string) e.Value)
        {
            e.Value = item;
            e.ParsingApplied = true;
            break;
        }    
    }
}