Colouring DataGridView Cells According to their Content in WinForms

Introduction

I have a data analysis tool which displays a fair amount of data; probably too much if I'm honest, but the data view isn't used much and is ordered so the recent stuff is immediately visible. It's just a "quick check" thing to show the details to back up the graphs which show the trends and so forth. Anyway, it was a pain to see quickly any anomalous values, so I thought I'd colour code them - and it's really easy to do.

Using the Code

Just hook up the CellPainting event handler to your DataGridView, and decide on the criteria and colours.

Here, I've used "negative is red", "zero is 'normal', and "positive is green":

/// <summary>
/// Set the cell background colour to make the ups and downs more visible.
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
private void dgvData_CellPainting(object sender, DataGridViewCellPaintingEventArgs e)
    {
    DataGridView dgv = sender as DataGridView;
    if (dgv != null && e.RowIndex >= 0)
        {
        if (e.ColumnIndex > 0)
            {
            Color c;
            if (e.Value != null && e.Value is Int32)
                {
                int value = (int) e.Value;
                if (value > 0)
                    {
                    c = Color.LightGreen;
                    }
                else if (value < 0)
                    {
                    c = Color.Salmon;
                    }
                else
                    {
                    c = dgv.DefaultCellStyle.BackColor;
                    }
                e.CellStyle.BackColor = c;
                }
            }
        }
    }

And I selected "LightGreen" and "Salmon" as they are more subtle and less intrusive than "vanilla" Color.Green and Color.Red. The check for the column index being nonzero just skips a date column which will never be coloured.

The grid view then takes care of itself: if the values change, they are always painted correctly without your code having to be concerned about them - and since they are only checked when they are painted, only the "visible" cells are involved at any time.

History

• 2018-04-23: First version
• 2018-04-23: Minor typos