Это код VB.NET, но объекты должны быть одинаковыми.
Private LVUsersLastHit As Point
Private Sub lvUsers_MouseUp(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles lvUsers.MouseUp
Me.LVUsersLastHit = e.Location
End Sub
Private Sub LvUsers_Doubleclick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles lvUsers.DoubleClick
Dim HTI As ListViewHitTestInfo = Me.lvUsers.HitTest(Me.LVUsersLastHit)
If HTI.Item Is Nothing OrElse HTI.SubItem Is Nothing Then Exit Sub 'nothing was dblclicked
MsgBox("doubleClicked the " & HTI.Item.ToString & " Item on the " & HTI.SubItem.ToString & " sub Item")
End Sub