功能：点击datagrid并且按住键盘上的ctrl或shift可选择多行

Public Class MyDataGridCLASS
Inherits DataGrid
Private m As New ArrayList

Public ReadOnly Property MultiSelectedIndex() As Integer()
  Get
   Return m.ToArray(GetType(Integer))
  End Get
End Property

Protected Overrides Sub OnMouseDown(ByVal e As System.Windows.Forms.MouseEventArgs)
  Debug.WriteLine("DataGrid has hit")
  Dim posdg As Point = New Point(e.X, e.Y)
  Dim hitDG As DataGrid.HitTestInfo = HitTest(posdg)
  If HitDataGrid(hitDG) Then
   MyBase.OnMouseDown(e)
   Debug.WriteLine("Mousedown has gogogo.....")
  End If
End Sub

Private Function HitDataGrid(ByVal Hit As DataGrid.HitTestInfo) As Boolean
  Try
   Select Case Me.ModifierKeys
Case Keys.Control
  If Hit.Row > -1 Then
   If m.IndexOf(Hit.Row) > -1 Then
m.Remove(Hit.Row)
Me.UnSelect(Hit.Row)
   Else
m.Add(Hit.Row)
Me.Select(Hit.Row)
   End If
  End If
  Return False
Case Keys.Shift
  If Hit.Row > -1 Then
   For Each IndexOld As Integer In m
Me.UnSelect(IndexOld)
   Next
   m.Clear()
   Dim i, intStep As Integer
   If Hit.Row > Me.CurrentRowIndex Then
intStep = 1
   Else
intStep = -1
   End If
   For i = Me.CurrentRowIndex To Hit.Row Step intStep
m.Add(i)
Me.Select(i)
   Next
  End If
  Return False
Case Else
  For Each index As Integer In m
   Me.UnSelect(index)
  Next
  m.Clear()
  If Hit.Type = DataGrid.HitTestType.RowHeader Then
   m.Add(Hit.Row)
  End If
  Return True
   End Select
  Catch ex As Exception
   Debug.WriteLine(ex.ToString)
  End Try
End Function
End Class