Question

How do I add a colgroup tag to the datagrid control so that I can style each column using css?

Answer 1

I thought this was addressed in .NET 3.5, but I can’t find any references. Anyways, here is a hand-rolled server control that allows you to specify colgroup…

public class ColGroupGridView : GridView
{
    private ColGroup _ColGroup = null;
    private ITemplate _ColGroupTemplate = null;

    [TemplateContainer(typeof(ColGroup))]
    public virtual ITemplate ColGroupTemplate
    {
        get { return _ColGroupTemplate; }
        set { _ColGroupTemplate = value; }
    }

    protected override void CreateChildControls()
    {
        base.CreateChildControls();
        _ColGroup = new ColGroup();
        ColGroupTemplate.InstantiateIn(_ColGroup);
    }

    protected override void Render(HtmlTextWriter writer)
    {
        // Get the base class's output
        StringWriter sw = new StringWriter();
        HtmlTextWriter htw = new HtmlTextWriter(sw);
        base.Render(htw);
        string output = sw.ToString();
        htw.Close();
        sw.Close();

        // Insert a <COLGROUP> element into the output
        int pos = output.IndexOf("<tr");

        if (pos != -1 && _ColGroup != null)
        {
            sw = new StringWriter();
            htw = new HtmlTextWriter(sw);
            _ColGroup.RenderPrivate(htw);
            output = output.Insert(pos, sw.ToString());
            htw.Close();
            sw.Close();
        }

        // Output the modified markup
        writer.Write(output);
    }
}

internal class ColGroup : WebControl, INamingContainer
{
    internal void RenderPrivate(HtmlTextWriter writer)
    {
        writer.Write("<colgroup>");
        base.RenderContents(writer);
        writer.Write("</colgroup>");
    }
}

Use it like this…

<custom:ColGroupGridView ... runat="server">
    <ColGroupTemplate>
        <col class="itemid" />
        <col class="cover-image" />
        <col class="title" />
        <col class="number" />
        <col class="year" />
        <col class="rating" />
        <col class="cgc-rating" />
        <col class="description" />
    </ColGroupTemplate>
    <!-- Rest of stuff here... -->
</custom:ColGroupGridView>

Source: Jeff Prosise’s Blog