Question

MVCContrib Grid中的优雅Action Syntax为我们提供了Empty()方法。但是，MvcContrib.UI.Grid.GridRenderer<T>.RenderHeader()的默认行为是在网格为空时隐藏表列标题。有没有一种方法可以在不存在不需要重大重构的数据时显示标题？

现在我听说默认隐藏标题并硬编码，但这对我来说并不酷。

顺便说一句，这就是幕后发生的事情（在MvcContrib.UI.Grid.GridRenderer<T>中）：

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

您可以覆盖ShouldRenderHeader()类的HtmlTableGridRenderer方法。

public class AlwaysRenderHeaderRenderer<T>
    : HtmlTableGridRenderer<T> where T : class
{
    protected override bool ShouldRenderHeader()
    {
        return true;
    }
}

<%= Html.Grid(Model).RenderUsing(new AlwaysRenderHeaderRenderer<TypeOfModel>()) %>

这种方法的副作用是当网格为空时，将呈现空的表体而不是消息。提供给Empty()的任何文本都将被忽略。这对我来说不是问题，因为无论如何我都在使用JavaScript操作客户端的表，但是要注意。

Answer 2

从HtmlTableGridRenderer继承时，您也可以覆盖RenderEmpty以消除Brant遇到的问题。

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

在自定义网格渲染器（子类GridRenderer<T>）中，使用以下覆盖：

/// <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();
}

请注意，WriteNoRecordsAvailable()是我的自定义方法，因此可以忽略它。

最后：

/// <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&lt;T&gt;"/> class.
/// </summary>
/// <param name="engines">The engines.</param>
public CrmHtmlTableGridRenderer(ViewEngineCollection engines)
    : base(engines)
{
    _engines = engines;
}

Answer 4

你不能只是注释掉检查，看它是否应该呈现标题。我错过了什么，或者你是否希望它始终显示标题？

如果有，那就注释掉那一行。

//if(! ShouldRenderHeader()) return false;

我没有查看所有代码，但是从您的代码片段看起来应该可以正常工作。

Answer 5

David's和Brant's答案的组合：

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();
}

MVCContrib Grid在空时显示标题？

5 个答案: