CustomComboBoxCellType cellType = new CustomComboBoxCellType();
string[] labels = new string[10];
for (int i = 0; i < labels.Length; i++)
{
    labels[i] = i.ToString();
}
cellType.Items = labels; fpSpread1.ActiveSheet.Cells["B2"].CellType = cellType;
fpSpread1.ActiveSheet.Columns[1].Width = 200;

public class CustomComboBoxCellType : EditBaseCellType
{
    public CustomComboBoxCellType()
    {
        ButtonAlign = ButtonAlign.Right;
        DropDownButton = true;
        SubEditor = new CheckedListBoxSubEditor();
    }

    public override Control GetEditorControl(FarPoint.Win.Spread.Appearance appearance, float zoomFactor)
    {
        GeneralEditor customEditor = new GeneralEditor();
        InitializeEditorControl(customEditor, appearance, zoomFactor);
        return customEditor;
    }

    public override void InitializeEditorControl(Control control, FarPoint.Win.Spread.Appearance appearance, float zoomFactor)
    {
        base.InitializeEditorControl(control, appearance, zoomFactor);

        GeneralEditor customEditor = (GeneralEditor)control;


        CheckedListBoxSubEditor checkedListBox = (CheckedListBoxSubEditor)customEditor.SubEditor;
        checkedListBox.Items.Clear();
        checkedListBox.Items.AddRange(Items);
    }

    public override object GetEditorValue()
    {
        if (SubEditor is CheckedListBoxSubEditor editor)
        {
            CheckedListBox.CheckedItemCollection checkedItems = editor.CheckedItems;
            int count = checkedItems.Count;
            if (count > 0)
            {
                StringBuilder sb = new StringBuilder();
                sb.Append(checkedItems[0].ToString());
                for (int i = 1; i < count; i++)
                {
                    sb.Append(", ");
                    sb.Append(checkedItems[i].ToString());
                }
                return sb.ToString();
            }

        }
        return null;
    }

    public override void SetEditorValue(object value)
    {
        if (SubEditor is CheckedListBoxSubEditor editor)
        {
            editor.ClearSelected();

            if (value is string text)
            {
                string[] items = text.Split(',', (char)StringSplitOptions.RemoveEmptyEntries);
                foreach (string item in items)
                {
                    int index = editor.FindString(item.Trim());
                    if (index >= 0)
                    {
                        editor.SetItemChecked(index, true);
                    }
                }
            }
        }
    }

    public object[] Items { get; set; }
}

public class CheckedListBoxSubEditor : CheckedListBox, ISubEditor, ISubEditorParentInfo
{
    public CheckedListBoxSubEditor()
    {
        SelectionMode = SelectionMode.One;
    }

    public Control EditorControl { get; set; }

    public event EventHandler ValueChanged;
    public event EventHandler CloseUp;

    public Point GetLocation(Rectangle rect)
    {
        return Point.Empty;
    }

    public Size GetPreferredSize()
    {
        Size size = GetPreferredSize(Size.Empty);
        if (EditorControl != null)
        {
            size.Width = EditorControl.Width;
        }
        return size;
    }

    public Control GetSubEditorControl()
    {
        return this;
    }

    public object GetValue()
    {
        return SelectedValue;
    }

    public void SetValue(object value)
    {
        SelectedValue = value;
    }
}