Question

I have extended the DataGridView cell to display the text from its Tag property in the corner (e.g. displaying the day number in the corner of a calendar) and would like to be able to specify the Color and opacity of the text.

To accomplish this I have added 2 properties to the subclassed DataGridView cell, however they are not storing their values at runtime. This is the DataGridViewCell and Column:

class DataGridViewLabelCell : DataGridViewTextBoxCell
{
    private Color _textColor;
    private int _opacity;

    public Color TextColor { get { return _textColor; } set { _textColor = value; } }
    public int Opacity { get { return _opacity; } set { _opacity = value; } }

    protected override void Paint(Graphics graphics,
                                  Rectangle clipBounds,
                                  Rectangle cellBounds,
                                  int rowIndex,
                                  DataGridViewElementStates cellState,
                                  object value,
                                  object formattedValue,
                                  string errorText,
                                  DataGridViewCellStyle cellStyle,
                                  DataGridViewAdvancedBorderStyle advancedBorderStyle,
                                  DataGridViewPaintParts paintParts)
    {
        // Call the base class method to paint the default cell appearance.
        base.Paint(graphics, clipBounds, cellBounds, rowIndex, cellState,
            value, formattedValue, errorText, cellStyle,
            advancedBorderStyle, paintParts);

        if (base.Tag != null)
        {
            string tag = base.Tag.ToString();
            Point point = new Point(base.ContentBounds.Location.X, base.ContentBounds.Location.Y);
            Font font = new Font("Arial", 25.0F, FontStyle.Bold);
            graphics.DrawString(tag, font, new SolidBrush(Color.FromArgb(_opacity, _textColor)), cellBounds.X, cellBounds.Y);
        }
    }
}

public class DataGridViewLabelCellColumn : DataGridViewColumn
{
    public DataGridViewLabelCellColumn(Color TextColor, int Opacity = 128)
    {
        DataGridViewLabelCell template = new DataGridViewLabelCell();
        template.TextColor = TextColor;
        template.Opacity = Opacity;
        this.CellTemplate = template;
    }
}

I add the columns as follows:

col = new DataGridViewLabelCellColumn(Color.Blue, 115);
dgv.Columns.Add(col);
col.HeaderText = "Saturday";
col.Name = "Saturday";

However, if I add a breakpoint to the graphics.DrawString line neither _textColor nor _opacity have a value. If I assign them default values as follows:

private Color _textColor = Color.Red;
private int _opacity = 128;

Then it works fine. How can I ensure that the values get stored in the CellTemplate?

Answer 1

I believe it’s because the CellTemplate is stored as a more generic DataGridViewCell, rather than the subclassed LabelCell. At any rate, storing the values on the Column and just referencing them from there works fine:

DataGridViewLabelCellColumn clm = (DataGridViewLabelCellColumn)base.OwningColumn;
int opacity = clm.Opacity;
Color textColor = clm.TextColor;
graphics.DrawString(tag, font, new SolidBrush(Color.FromArgb(opacity, textColor)), cellBounds.X, cellBounds.Y);