Pasting Excel Clipboard Text to Databound DataGridView and Entity Framework Validation - vb.net

Question

In a Windows Forms project being developed in Visual Studio 2010, I have a DataGridView bound to a BindingSource whose DataSource is a BindingList(Of T). T is an entity from an Entity Framework 5 model.
My entities implement INotifyPropertyChanged and IDataErrorInfo.
My users are Excel heads and insist that I provide for the pasting of Excel data into the grids in use in our application.
So, I set out with a couple of simple rules.
Mimic as closely as possible the copy & paste behavior within Excel.
Pasting data into a new row in a DataGridView should create and validate new entities of the type represented in the grid.
I've come a long way with this but have now bumped up against something I can't figure out.
Judging by what information I can find, it seems clear that when pasting into a bound grid that the underlying data source should be the target of your edits and creates.
Or should it?
I've tried both ways.
When targeting the cells themselves, I hoped that I could write the routine such that the validation events built into DataGridView would fire when needed, whether I was editing an existing row or creating a new one.
I shortly discovered that it wasn't working as expected because CellValidating doesn't fire until the cell loses focus.
While pasting, I'd like to validate the cell at the moment a value is pasted into it - cancelling the rest of the paste operation if it fails.
When targeting the underlying data source (a row's DataBoundItem cast as the appropriate entity type), I can create new entities from the clipboard data and validate them before committing changes to the DbContext.
In either case, when validation fails, the DataGridView seems to have lost the previous value for the cell.
If validation fails the user is prompted and the routine exits. I'd like for user to be able to hit the Esc key to return the previous value for the cell, but the cell remains empty.
Does anyone know why the previous value is no longer available when editing a cell's value programatically?
Here's what I'm doing so far. I am forcing the validation events to fire by calling the form's .Validate method. I don't know if I should be doing that or not. It is incomplete in that I am not yet handling new rows:
Private Sub PasteFromClipboard(ByVal sender As Object, ByVal e As KeyEventArgs)
Dim dgv = TryCast(sender, DataGridView)
If Not IsNothing(dgv) Then
If dgv.SelectedCells.Count > 0 Then
Dim rowSplitter = {ControlChars.Cr, ControlChars.Lf}
Dim columnSplitter = {ControlChars.Tab}
Dim topLeftCell = CopyPasteFunctions.GetTopLeftSelectedCell(dgv.SelectedCells)
If Not IsNothing(topLeftCell) Then
Dim data = Clipboard.GetData(DataFormats.Text)
If Not IsNothing(data) Then
Dim columnIndex = topLeftCell.ColumnIndex
Dim rowIndex = topLeftCell.RowIndex
Dim columnCount = dgv.Columns.Count
Dim rowCount = dgv.Rows.Count
'Split clipboard data into rows
Dim rows = data.ToString.Split(rowSplitter, StringSplitOptions.RemoveEmptyEntries)
For i = 0 To rows.Length - 1
'Split row into cell values
Dim values = rows(i).Split(columnSplitter)
For j = 0 To values.Length - 1
If (j <= (columnCount - 1)) AndAlso (i <= (rowCount - 1)) Then
Dim cell = dgv.Rows(rowIndex + i).Cells(columnIndex + j)
dgv.CurrentCell = cell
dgv.BeginEdit(False)
cell.Value = values(j)
If Not Me.Validate() Then
dgv.CancelEdit()
Exit Sub
Else
dgv.EndEdit()
End If
Else
Debug.Print(String.Format("RowIndex: {0}, ColumnIndex: {1}", i, j))
End If
Next
Next
End If
End If
End If
End If
End Sub
Public Module CopyPasteFunctions
Public Function GetTopLeftSelectedCell(ByVal cells As DataGridViewSelectedCellCollection) As DataGridViewCell
If Not IsNothing(cells) AndAlso cells.Count > 0 Then
Dim cellList = (From c In cells.Cast(Of DataGridViewCell)()
Order By c.RowIndex, c.ColumnIndex
Select c).ToList
Return cellList(0)
End If
Return Nothing
End Function
End Module
Thanks for any help on this. Hopefully others are working with EF5 and Winforms. If not, I'm on my own!

Answer 1

This gets the job done when the grid contains one column.
It is assumed that the developer is handling the CellValidating event correctly, meaning that if validation fails the event is cancelled.
This routine closely resembles the copy and paste behavior one observes in Excel.
Private Sub PasteFromClipboard(ByVal sender As Object, ByVal e As KeyEventArgs)
Dim dgv = TryCast(sender, DataGridView)
If Not IsNothing(dgv) AndAlso Clipboard.ContainsText Then
If dgv.SelectedCells.Count > 0 Then
Dim rowSplitter = {ControlChars.NewLine}
Dim columnSplitter = {ControlChars.Tab}
Dim topLeftCell = CopyPasteFunctions.GetTopLeftSelectedCell(dgv.SelectedCells)
If Not IsNothing(topLeftCell) Then
Dim clipBoardText = Clipboard.GetText(TextDataFormat.Text)
Dim columnIndex = topLeftCell.ColumnIndex
Dim rowIndex = topLeftCell.RowIndex
Dim columnCount = dgv.Columns.Count
Dim rows = clipBoardText.Split(rowSplitter, StringSplitOptions.None)
For i = 0 To rows.Length - 2
'Split row into cell values
Dim values = rows(i).Split(columnSplitter)
Dim rowCount = dgv.Rows.Count
For j = 0 To values.Length - 1
If (i <= (rowCount - 1)) AndAlso ((j + 1) <= columnCount) Then
Dim cell = dgv.Rows(rowIndex + i).Cells(columnIndex + j)
dgv.CurrentCell = cell
dgv.BeginEdit(False)
dgv.EditingControl.Text = values(j)
If Not Me.Validate() Then
Exit Sub
Else
dgv.EndEdit()
End If
End If
Next
Next
End If
End If
End If
End Sub
Public Module CopyPasteFunctions
Public Function GetTopLeftSelectedCell(ByVal cells As DataGridViewSelectedCellCollection) As DataGridViewCell
If Not IsNothing(cells) AndAlso cells.Count > 0 Then
Dim cellList = (From c In cells.Cast(Of DataGridViewCell)()
Order By c.RowIndex, c.ColumnIndex
Select c).ToList
Return cellList(0)
End If
Return Nothing
End Function
End Module

Answer 2

I would parse the data update the Entity Framework object with new objects of type that fits your Entity model. Then just save the Entity object and rebind your DGV.