WinForms Data Grid - Select multiple rows by dragging the mouse in RowSelect mode

C#
using DevExpress.Utils;
using DevExpress.XtraGrid;
using DevExpress.XtraGrid.Registrator;
using DevExpress.XtraGrid.Views.Base;
using DevExpress.XtraGrid.Views.Base.Handler;
using DevExpress.XtraGrid.Views.Grid;
using DevExpress.XtraGrid.Views.Grid.ViewInfo;
using System.ComponentModel;
using System.Drawing;
using System.Windows.Forms;

namespace DXApplication3
{
    [ToolboxItem(true)]
    public class CustomGrid : GridControl
    {
        protected override BaseView CreateDefaultView()
        {
            return CreateView("CustomGridView");
        }
        protected override void RegisterAvailableViewsCore(InfoCollection collection)
        {
            base.RegisterAvailableViewsCore(collection);
            collection.Add(new CustomGridViewInfoRegistrator());
        }
    }

    public class CustomGridViewInfoRegistrator : GridInfoRegistrator
    {
        public override string ViewName
        {
            get
            {
                return "CustomGridView";
            }
        }
        public override BaseView CreateView(GridControl grid)
        {
            return new CustomGridView(grid);
        }
        public override BaseViewHandler CreateHandler(BaseView view)
        {
            return new CustomGridViewHandler(view as CustomGridView);
        }
    }

    public class CustomGridView : GridView
    {
        public virtual bool IsRowSelect { get { return IsMultiSelect && OptionsSelection.MultiSelectMode == GridMultiSelectMode.RowSelect; } }
        public CustomGridView()
        {
        }
        public CustomGridView(GridControl grid) : base(grid)
        {
        }
        protected override string ViewName
        {
            get
            {
                return "CustomGridView";
            }
        }
        internal new void StartAccessSelection()
        {
            base.StartAccessSelection();
        }
        public override EditorShowMode GetShowEditorMode()
        {
            if (OptionsBehavior.EditorShowMode == EditorShowMode.Default && IsRowSelect)
                return EditorShowMode.Click;
            return base.GetShowEditorMode();
        }
    }

    public class CustomGridViewHandler : DevExpress.XtraGrid.Views.Grid.Handler.GridHandler
    {
        private GridHitInfo mouseDownHitInfo;
        public new CustomGridView View { get { return base.View as CustomGridView; } }
        public CustomGridViewHandler(GridView view) : base(view)
        {
        }
        protected override bool OnMouseDown(MouseEventArgs ev)
        {
            var result = base.OnMouseDown(ev);
            if (ev.Button == MouseButtons.Left && Control.ModifierKeys == Keys.None && View.IsRowSelect && DownPointHitInfo.InRowCell)
                mouseDownHitInfo = DownPointHitInfo;
            else
                mouseDownHitInfo = null;
            return result;
        }
        protected override bool OnMouseMove(MouseEventArgs ev)
        {
            var result = base.OnMouseMove(ev);
            if (!result && ev.Button == MouseButtons.Left && mouseDownHitInfo != null)
            {
                var dragSize = SystemInformation.DragSize;
                var dragRect = new Rectangle(
                    new Point(mouseDownHitInfo.HitPoint.X - dragSize.Width / 2, mouseDownHitInfo.HitPoint.Y - dragSize.Height / 2),
                    dragSize);
                if (!dragRect.Contains(ev.Location))
                {
                    mouseDownHitInfo = null;
                    View.StartAccessSelection();
                    result = true;
                }
            }
            return result;
        }
    }
}

Visual Basic
Imports DevExpress.Utils
Imports DevExpress.XtraGrid
Imports DevExpress.XtraGrid.Registrator
Imports DevExpress.XtraGrid.Views.Base
Imports DevExpress.XtraGrid.Views.Base.Handler
Imports DevExpress.XtraGrid.Views.Grid
Imports DevExpress.XtraGrid.Views.Grid.ViewInfo
Imports System.ComponentModel
Imports System.Drawing
Imports System.Windows.Forms

Namespace DXApplication3

    <ToolboxItem(True)>
    Public Class CustomGrid
        Inherits GridControl

        Protected Overrides Function CreateDefaultView() As BaseView
            Return CreateView("CustomGridView")
        End Function

        Protected Overrides Sub RegisterAvailableViewsCore(ByVal collection As InfoCollection)
            MyBase.RegisterAvailableViewsCore(collection)
            collection.Add(New CustomGridViewInfoRegistrator())
        End Sub
    End Class

    Public Class CustomGridViewInfoRegistrator
        Inherits GridInfoRegistrator

        Public Overrides ReadOnly Property ViewName As String
            Get
                Return "CustomGridView"
            End Get
        End Property

        Public Overrides Function CreateView(ByVal grid As GridControl) As BaseView
            Return New CustomGridView(grid)
        End Function

        Public Overrides Function CreateHandler(ByVal view As BaseView) As BaseViewHandler
            Return New CustomGridViewHandler(TryCast(view, CustomGridView))
        End Function
    End Class

    Public Class CustomGridView
        Inherits GridView

        Public Overridable ReadOnly Property IsRowSelect As Boolean
            Get
                Return IsMultiSelect AndAlso OptionsSelection.MultiSelectMode = GridMultiSelectMode.RowSelect
            End Get
        End Property

        Public Sub New()
        End Sub

        Public Sub New(ByVal grid As GridControl)
            MyBase.New(grid)
        End Sub

        Protected Overrides ReadOnly Property ViewName As String
            Get
                Return "CustomGridView"
            End Get
        End Property

        Friend Overloads Sub StartAccessSelection()
            MyBase.StartAccessSelection()
        End Sub

        Public Overrides Function GetShowEditorMode() As EditorShowMode
            If OptionsBehavior.EditorShowMode = EditorShowMode.Default AndAlso IsRowSelect Then Return EditorShowMode.Click
            Return MyBase.GetShowEditorMode()
        End Function
    End Class

    Public Class CustomGridViewHandler
        Inherits Views.Grid.Handler.GridHandler

        Private mouseDownHitInfo As GridHitInfo

        Public Overloads ReadOnly Property View As CustomGridView
            Get
                Return TryCast(MyBase.View, CustomGridView)
            End Get
        End Property

        Public Sub New(ByVal view As GridView)
            MyBase.New(view)
        End Sub

        Protected Overrides Function OnMouseDown(ByVal ev As MouseEventArgs) As Boolean
            Dim result = MyBase.OnMouseDown(ev)
            If ev.Button = MouseButtons.Left AndAlso Control.ModifierKeys = Keys.None AndAlso View.IsRowSelect AndAlso DownPointHitInfo.InRowCell Then
                mouseDownHitInfo = DownPointHitInfo
            Else
                mouseDownHitInfo = Nothing
            End If

            Return result
        End Function

        Protected Overrides Function OnMouseMove(ByVal ev As MouseEventArgs) As Boolean
            Dim result = MyBase.OnMouseMove(ev)
            If Not result AndAlso ev.Button = MouseButtons.Left AndAlso mouseDownHitInfo IsNot Nothing Then
                Dim dragSize = SystemInformation.DragSize
                Dim dragRect = New Rectangle(New Point(mouseDownHitInfo.HitPoint.X - dragSize.Width \ 2, mouseDownHitInfo.HitPoint.Y - dragSize.Height \ 2), dragSize)
                If Not dragRect.Contains(ev.Location) Then
                    mouseDownHitInfo = Nothing
                    View.StartAccessSelection()
                    result = True
                End If
            End If

            Return result
        End Function
    End Class
End Namespace

C#
using System;
using System.Data;

namespace DXApplication3
{
    public partial class Form1 : DevExpress.XtraEditors.XtraForm
    {
        public Form1()
        {
            InitializeComponent();
            customGrid1.DataSource = CreateTable(42);
            customGridView1.OptionsSelection.MultiSelect = true;
        }
        private DataTable CreateTable(int RowCount)
        {
            DataTable tbl = new DataTable();
            tbl.Columns.Add("Name", typeof(string));
            tbl.Columns.Add("ID", typeof(int));
            tbl.Columns.Add("Number", typeof(int));
            tbl.Columns.Add("Date", typeof(DateTime));
            for (int i = 0; i < RowCount; i++)
                tbl.Rows.Add(new object[] { String.Format("Name{0}", i), i, i % 4, DateTime.Now.AddDays(i) });
            return tbl;
        }
    }
}

Visual Basic
Imports System.Data

Namespace DXApplication3

    Public Partial Class Form1
        Inherits DevExpress.XtraEditors.XtraForm

        Public Sub New()
            InitializeComponent()
            customGrid1.DataSource = CreateTable(42)
            customGridView1.OptionsSelection.MultiSelect = True
        End Sub

        Private Function CreateTable(ByVal RowCount As Integer) As DataTable
            Dim tbl As DataTable = New DataTable()
            tbl.Columns.Add("Name", GetType(String))
            tbl.Columns.Add("ID", GetType(Integer))
            tbl.Columns.Add("Number", GetType(Integer))
            tbl.Columns.Add("Date", GetType(Date))
            For i As Integer = 0 To RowCount - 1
                tbl.Rows.Add(New Object() {String.Format("Name{0}", i), i, i Mod 4, Date.Now.AddDays(i)})
            Next

            Return tbl
        End Function
    End Class
End Namespace