MVCContrib Grid showing headers when empty? - asp.net-mvc

Question

The elegant Action Syntax in the MVCContrib Grid gives us the Empty() method. However, the default behavior of MvcContrib.UI.Grid.GridRenderer<T>.RenderHeader() is to hide the table column headers when the grid is empty. Is there a way to show headers when data is not present that does not require a major refactoring?
Now I have heard of hiding the headers by default and hard-coding something but this is not cool to me.
By the way, this is what is happening under the hood (in MvcContrib.UI.Grid.GridRenderer<T>):
protected virtual bool RenderHeader()
{
//No items - do not render a header.
if(! ShouldRenderHeader()) return false;
RenderHeadStart();
foreach(var column in VisibleColumns())
{
//Allow for custom header overrides.
if(column.CustomHeaderRenderer != null)
{
column.CustomHeaderRenderer(new RenderingContext(Writer, Context, _engines));
}
else
{
RenderHeaderCellStart(column);
RenderHeaderText(column);
RenderHeaderCellEnd();
}
}
RenderHeadEnd();
return true;
}
protected virtual bool ShouldRenderHeader()
{
return !IsDataSourceEmpty();
}
protected bool IsDataSourceEmpty()
{
return DataSource == null || !DataSource.Any();
}

Answer 1

You can override the ShouldRenderHeader() method of the HtmlTableGridRenderer class.
public class AlwaysRenderHeaderRenderer<T>
: HtmlTableGridRenderer<T> where T : class
{
protected override bool ShouldRenderHeader()
{
return true;
}
}
<%= Html.Grid(Model).RenderUsing(new AlwaysRenderHeaderRenderer<TypeOfModel>()) %>
A side effect of this approach is that when the grid is empty, an empty table body will be rendered instead of a message. Any text provided to Empty() is ignored. This wasn't a problem for me since I'm manipulating the table on the client side with JavaScript anyway, but be warned.

Answer 2

When inheriting from HtmlTableGridRenderer you can also override RenderEmpty to eliminate the problem Brant ran into.
protected override void RenderEmpty()
{
RenderHeadStart();
foreach(var column in VisibleColumns())
{
RenderHeaderCellStart(column);
RenderHeaderText(column);
RenderHeaderCellEnd();
}
RenderHeadEnd();
RenderBodyStart();
RenderText("<tr><td colspan=\"" + VisibleColumns().Count() + "\">" + GridModel.EmptyText + "</td></tr>");
RenderBodyEnd();
}

Answer 3

In your custom Grid Renderer (subclass GridRenderer<T>) use overrides like these:
/// <summary>
/// Renders the <c>table</c> header.
/// </summary>
/// <returns>
/// Returns the negative of the results
/// of <see cref="GridRenderer<T>.IsDataSourceEmpty"/>.
/// </returns>
/// <remarks>
/// The return value of <see cref="GridRenderer<T>.IsDataSourceEmpty"/>
/// in this override has no effect on whether the Grid header is rendered.
///
/// However, this return value is used
/// by <see cref="GridRenderer<T>.Render"/>
/// to run <see cref="GridRenderer<T>.RenderItems"/>
/// or <see cref="GridRenderer<T>.RenderEmpty"/>.
/// </remarks>
protected override bool RenderHeader()
{
RenderHeadStart();
foreach(var column in VisibleColumns())
{
//Allow for custom header overrides.
if(column.CustomHeaderRenderer != null)
{
column.CustomHeaderRenderer(new RenderingContext(Writer, Context, _engines));
}
else
{
RenderHeaderCellStart(column);
RenderHeaderText(column);
RenderHeaderCellEnd();
}
}
RenderHeadEnd();
return !base.IsDataSourceEmpty();
}
…
protected override void RenderEmpty()
{
RenderBodyStart();
WriteNoRecordsAvailable(base.Writer, this._numberOfTableColumns);
RenderBodyEnd();
}
Note that WriteNoRecordsAvailable() is my custom method so it can be ignored.
Finally:
/// <summary>
/// This private member is duplicated
/// in order to override <see cref="GridRenderer<T>.RenderHeader"/>.
/// </summary>
readonly ViewEngineCollection _engines;
…
/// <summary>
/// Initializes a new instance of the <see cref="CrmHtmlTableGridRenderer<T>"/> class.
/// </summary>
/// <param name="engines">The engines.</param>
public CrmHtmlTableGridRenderer(ViewEngineCollection engines)
: base(engines)
{
_engines = engines;
}

Answer 4

Can't you just comment out the check to see if it should render the header. Am I missing something or do you want it to always display the header?
If so then comment out that line.
//if(! ShouldRenderHeader()) return false;
I haven't looks at all the code but from your code snippet it seems like that should work.

Answer 5

A combination of David's and Brant's answers:
protected override bool ShouldRenderHeader()
{
return true;
}
// Oddly Render relies on ShouldRenderHeader to return IsDataSourceEmpty
// so RenderItems will always be called.
protected override void RenderItems()
{
if (IsDataSourceEmpty())
RenderEmpty();
else
base.RenderItems();
}
protected override void RenderEmpty()
{
RenderBodyStart();
RenderText("<tr><td colspan=\"" + VisibleColumns().Count() + "\">" + GridModel.EmptyText + "</td></tr>");
RenderBodyEnd();
}