Is there a way to force a DataGridView to fire its CellFormatting event for all cells?

Question

We use the CellFormatting event to colour code cells in various grids all over our application.

We've got some generic code which handles export to Excel (and print) but it does it in Black & White. Now we want to change this and pick up the colour from the grids.

This question & answer has helped (and it works) ... except there's a problem with larger grids that extend beyond a single screen. The portions of the grid which haven't yet been displayed on screen are (logically) never getting their CellFormatting code fired, and so their underlying colour never gets set. As a result, in Excel, the colour coding fizzles out half way down the page.

Seems there are three solutions:

1) Tell the user he has to scroll to all parts of the grid before doing an Export to Excel. Ha! Not a serious solution

2) Programmatically scroll to all parts of the grid before doing an Export to Excel. Only slighly less horrible than (1)

3) In our Export to Excel code, fire something at the top which tells the DataGridView to paint/format its entire area e.g.

  MyDataGridView.FormatAllCells()

Is there something that does something like this???

Oh, and there is a fourth option but this will involve touching a massive amount of existing code:

4) Stop using CellFormatting event, format the cells at load time. Problem with this is we'd have to retool every grid in our application since CellFormatting is the way we've done it since year dot.

Answer 1

I have a possible solution - In your export function access the Cell.FormattedValue property of each cell. According to Microsoft, this forces the CellFormatting event to fire.

Answer 2

As noted in the other answers, accessing the DataGridViewCell.FormattedValue is indeed an easy way to force the CellFormatting event to be (re-)called for a specific cell. In my case, however, this property was also leading to undesirable side-effects involving the auto-resizing of the columns. While searching a long time for a workable solution, I finally encountered the following magic methods that work perfectly: DataGridView.Invalidate(), DataGridView.InvalidateColumn(), DataGridView.InvalidateRow(), and DataGridView.InvalidateCell().

These 4 methods force the CellFormatting event to be re-called only for the specified scope (cell, column, row, or whole table), and also without causing any nasty auto-resizing artifacts.

Answer 3

Assuming, as @DavidHall suggests, there is no magic .FormatAllCells our only option is to stop using CellFormatting.

However, new problem here is that applying cell style formatting during load doesn’t seem to have any effect. Lots of posts out there if you Google it. Also they point out that if you put the same code under a button on the form and click it after loading (instead of in the load, the code will work ... so the grid has to be visible before styling can apply). Most advice on the topic suggests you use ... drumroll ... CellFormatting. Aargh!

Eventually found a post which suggests using the DataBindingComplete event of the grid. And this works.

Admittedly, this solution is a variant of my unwanted option "4".

Answer 4

I had the same problem and I've ended up with something quite similar to your solution #4. like you, I've used the DataBindingComplete event. but, Since I've used Extension method, the changes in the existing code are bearable:

internal static class DataGridViewExtention
{
    public static void SetGridBackColorMyStyle(this DataGridView p_dgvToManipulate)
    {
        p_dgvToManipulate.RowPrePaint += p_dgvToManipulate_RowPrePaint;
        p_dgvToManipulate.DataBindingComplete += p_dgvToManipulate_DataBindingComplete;
    }

    // for the first part - Coloring the whole grid I used the `DataGridView.DataBindingComplete` event:
    private static void p_dgvToManipulate_DataBindingComplete(object sender, DataGridViewBindingCompleteEventArgs e)
    {
        foreach (DataGridViewRow objCurrRow in ((DataGridView)sender).Rows)
        {
            // Get the domain object from row 
            DomainObject objSelectedItem = (DomainObject)objCurrRow.DataBoundItem;

            // if item is valid ....
            if objSelectedItem != null)
            {
                // Change backcolor of row using my method
                objCurrRow.DefaultCellStyle.BackColor = GetColorForMyRow(objSelectedItem);
            }
        }
    }

    // for the second part (disabling the Selected row from effecting the BackColor i've setted myself, i've used `DataGridView.RowPrePaint` event:
    private static void p_dgvToManipulate_RowPrePaint(object sender, DataGridViewRowPrePaintEventArgs e)
    {
        // If current row about to be painted is selected by user
        if (((DataGridView)sender).Rows[e.RowIndex].Selected)
        {
            // Get current grid row
            var objGridRow = ((DataGridView)sender).Rows[e.RowIndex];

            // Get selectedItem
            DomainObject objSelectedItem = (DomainObject)objGridRow.DataBoundItem;

            // if item is valid ....
            if (objSelectedItem != null && objSelectedItem.ObjectId != 0)
            {
                // Set color for row instead of "DefaultCellStyle" (same color as we used at DataBindingComplete event)
                objGridRow.DefaultCellStyle.SelectionBackColor = GetColorForMyRow(objSelectedItem);
            }

            // Since the selected row is no longer unique, we need to let the used to identify it by making the font Bold
            objGridRow.DefaultCellStyle.Font = new Font(((DataGridView)sender).Font.FontFamily, ((DataGridView)sender).Font.Size, FontStyle.Bold);
        }
        // If current row is not selected by user
        else
        {
            // Make sure the Font is not Bold. (for not misleading the user about selected row...)
            ((DataGridView)sender).Rows[e.RowIndex].DefaultCellStyle.Font = new Font(((DataGridView)sender).Font.FontFamily,
                                                                                   ((DataGridView)sender).Font.Size, FontStyle.Regular);
        }
    }
}

Answer 5

A possible solution if you do want to reuse the formatting provided during the Cellformatting-event (e.g. the cellstyle-elements like fontbold and backgroundcolor). These cellstyles seem to be only available between the 'cellformatting' and 'cellpainting' events but not in the datagridview-cell's style itself..

Capture the cellstyles during the cellformatting-event with a second handler like this:

1. in the exportmodule add a shared list, array or dictionary to store the cellstyles:

   Dim oDataGridFormattingDictionary as  Dictionary(Of String, DataGridViewCellStyle) = nothing
   

2. initialize the dictionary and add a second handler to the datagridview in your printing or export-code. In vb.net something like this:

    oDataGridFormattingDictionary = New Dictionary(Of String, DataGridViewCellStyle)
    AddHandler MyDatagridviewControl.CellFormatting, AddressOf OnPrintDataGridView_CellFormatting
   

3. Add the code for the handler

   Private Sub OnPrintDataGridView_CellFormatting(ByVal sender As Object, ByVal e As System.Windows.Forms.DataGridViewCellFormattingEventArgs)
   If e.RowIndex > -1 AndAlso e.ColumnIndex > -1 AndAlso Not e.CellStyle Is Nothing Then
      If Not oDataGridFormattingDictionary Is Nothing andalso oDataGridFormattingDictionary.ContainsKey(e.RowIndex & "_" & e.ColumnIndex) = False Then
       oDataGridFormattingDictionary.Add(e.RowIndex & "_" & e.ColumnIndex, e.CellStyle)
      End If
   End If
   End Sub
   

4. Very important: to make sure the original cellformating-event (AND the second cellformatting-handler after that) are actually called you have to request the formattedvalue for each cell that you want to print (e.g.

   oValue = Datagridview.rows(printRowIndex).Cells(printColumnIndex).FormattedValue)
   

   !

5. When printing you can now check if the cell has formatting. E.g.:

   if not oDataGridFormattingDictionary is nothing andalso oDataGridFormattingDictionary.ContainsKey(printRowIndex & "_" & printColumnIndex) Then
   ... the cellstyle is accesible via:
   oDataGridFormattingDictionary(printRowIndex & "_" & printColumnIndex)
   end if 
   

6. at the end of the export or printcode remove the handler and set the dictionary to nothing

   RemoveHandler DirectCast(itemToPrint.TheControl, DataGridView).CellFormatting, AddressOf OnPrintDataGridView_CellFormatting
   oDataGridFormattingDictionary = nothing