Introduction

The .NET framework provides quite a rich collection of UI controls and components for WinFroms development. There is one particular control that has been missing. I am talking about color-picker control with drop down color selection capabilities, just like the one used within the Visual Studio .NET property browser for editing Color-typed properties.

A color picker control was developed by Palo Mraz and was published in this website. I wanted to use this control in a DataGridView but I couldn’t find any example on how to do it. The only available examples on how to use custom control in DataGridView were to do with textual controls. This custom control involves graphics and not just text. I have decided to publish this article for the benefit of other fellow developers who would like to have a color picker combo box hosted by a DataGridView.

Background

For those of you who want to get some background on the color picker combo box please refer to “The ColorPicker WinForms Control” article in http://www.codeproject.com/KB/cpp/a_colorpicker.aspx

You can get background on how to host custom controls in DataGridView cells in http://msdn2.microsoft.com/en-us/library/7tas5c80.aspx

Color Picker in DataGridView

The core requirement for my project was to display the same drop down color selector that is used within WinForm’s PropertyGrid control inside a DataGridView.

The DataGridView control provides several properties that you can use to adjust the appearance and basic behavior (look and feel) of its cells, rows, and columns. My requirement was to show the color itself next to a text showing the color’s name.

In order to do that I had to implement owner drawing for the control and extend its capabilities by creating custom cells, columns, and rows.

class ColorPickerColumn

This class creates a custom column for hosting a column of color picker cells. It inherits from DataGridViewColumn and overrides the property CellTemplate.

public override DataGridViewCell CellTemplate
{
get
{
return base.CellTemplate;
}
set
{
// Ensure that the cell used for the template is a ColorPickerCell.
if (value != null &&
!value.GetType().IsAssignableFrom(typeof(ColorPickerCell)))
{
throw new InvalidCastException("Must be a ColorPicker");
}
base.CellTemplate = value;
}
}

class ColorPickerCell

This class creates a custom cell for hosting the color picker combo box and it inherits from DataGridViewTextBoxCell. In order to draw the content of the cell in the way I wanted I overrided the paint method.

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 protected override void Paint(Graphics graphics,
Rectangle clipBounds, Rectangle cellBounds, int rowIndex,
DataGridViewElementStates elementState, object value,
object formattedValue, string errorText,
DataGridViewCellStyle cellStyle,
DataGridViewAdvancedBorderStyle advancedBorderStyle,
DataGridViewPaintParts paintParts)
{
formattedValue = null;
base.Paint(graphics, clipBounds, cellBounds, rowIndex, elementState, value, formattedValue,
errorText, cellStyle, advancedBorderStyle, paintParts);
Rectangle ColorBoxRect = new Rectangle();
RectangleF TextBoxRect = new RectangleF();
GetDisplayLayout(cellBounds, ref ColorBoxRect, ref TextBoxRect);
//// Draw the cell background, if specified.
if ((paintParts & DataGridViewPaintParts.Background) ==
DataGridViewPaintParts.Background)
{
SolidBrush cellBackground;
if (value != null && value.GetType() == typeof(Color))
{
cellBackground = new SolidBrush((Color)value);
}
else
{
cellBackground =  new SolidBrush(cellStyle.BackColor);
}
graphics.FillRectangle(cellBackground, ColorBoxRect);
graphics.DrawRectangle(Pens.Black, ColorBoxRect);
Color lclcolor=(Color)value;
graphics.DrawString(lclcolor.Name.ToString(), cellStyle.Font, System.Drawing.Brushes.Black, TextBoxRect);
cellBackground.Dispose();
}
}

The other method that I had to override is ParseFormattedValue. When the user picks a custom color from the list he or she gets a Hex number of this color. There is a slight problem with this number: it doesn’t get the 0x prefix added to it. This is causing the method System.Number.StringToNumber to generate an exception. The .NET environment tries to convert this string to an integer and fails as without the 0x prefix it cannot be regarded as a Hex number hence this method adds the prefix when required.

public override object ParseFormattedValue(object formattedValue, DataGridViewCellStyle cellStyle,
System.ComponentModel.TypeConverter formattedValueTypeConverter,
System.ComponentModel.TypeConverter valueTypeConverter)
{
int result;
string number = "0x" + formattedValue.ToString();
if (int.TryParse(formattedValue.ToString(), System.Globalization.NumberStyles.HexNumber, null, out result))
//Hex number
return base.ParseFormattedValue("0x" + formattedValue.ToString(), cellStyle, formattedValueTypeConverter, valueTypeConverter);
else
return base.ParseFormattedValue(formattedValue, cellStyle, formattedValueTypeConverter, valueTypeConverter);
}

class ColorPickerControl

This class creates the custom control to be hosted by the ColorPickerCell. It implements the interface IDataGridViewEditingControl and overrides the OnLeave event of the original ColorPicker control. OnLeave – This event calls NotifyDataGridViewOfValueChange to notify the DataGridView that the contents of the cell have changed.

protected override void OnLeave(EventArgs eventargs)
{
// Notify the DataGridView that the contents of the cell
// have changed.
base.OnLeave(eventargs);
NotifyDataGridViewOfValueChange();
}

Using the Code

I created a form named ExampleForm containing a DataGridView control. This grid has two columns: the first is a simple textbox column and the second is the ColorPicker column. In this form I demonstrate how to load and save the data containing colors and names to and from xml file named ColorData.xml. The file should be stored in the same folder of the excutable.