Using a Combobox to Select Colors

Introduction

This is a short article on how to use a combo box control to display and select all the named colors. A small strip of the color and its name for all the known colors is shown in the drop down of the combo box control as shown below.



The combo box control has a DrawItem event which needs to be implemented in the code to achieve this. There is a property called DrawMode for the combo box control which determines whether the operating system or the code will handle the drawing of the items in the list. This property must be set to 'OwnerDrawFixed' using the properties window in order for the DrawItem event implementation to be called.


Sample application

The solution contains only a single project and that project contains a single form. On the form, I have a button, the click of which will populate the combo box with all the named colors in the Color struct. I am using the selected color for changing the background color of a panel on the form.

The button click implementation is as shown below. I have used reflection to get a collection of all the colors in System.Drawing.Color structure. The color names are then added to the combo box list.

private void btnLoad_Click(object sender, EventArgs e)
{
    ArrayList ColorList = new ArrayList();
    Type colorType = typeof(System.Drawing.Color);
    PropertyInfo[] propInfoList =                       colorType.GetProperties(BindingFlags.Static |BindingFlags.DeclaredOnly | BindingFlags.Public);
    foreach (PropertyInfo c in propInfoList)
    {
        this.cmbboxClr.Items.Add(c.Name);
    }
}

In the combo box control's DrawItem event, the Graphics object (can be obtained through the Graphics property of the DrawItemEventArgs) is used to draw a strip of the named color using its FillRectangle method. The DrawString method is used to add the name of the color. The DrawItem event will be triggered for each item added to the combo box.

private void cmbboxClr_DrawItem(object sender, DrawItemEventArgs e)
{
    Graphics g = e.Graphics;
    Rectangle rect = e.Bounds;
    if (e.Index >= 0)
    {
       string n = ((ComboBox)sender).Items[e.Index].ToString();
       Font f = new Font("Arial", 9, FontStyle.Regular);
       Color c = Color.FromName(n);
       Brush b = new SolidBrush(c);
       g.DrawString(n, f, Brushes.Black, rect.X, rect.Top);
   g.FillRectangle(b, rect.X + 110, rect.Y + 5, rect.Width - 10,                               rect.Height - 10);
    }
}

A snap shot of the sample form:




You can download the full project and open in Visual studio 2005 for more details.