的WebGrid：无法从'拉姆达前pression'转换';动态的，对象＆gt;＆System.Func LT“ [英] WebGrid: cannot convert from 'lambda expression' to 'System.Func<dynamic,object>'

问题描述

我想处理一个ASP.NET MVC3 WinGrid呈现时可能为null一个DateTime的情况。尝试设置WebGridColumn时，我得到一个错误。我有一个，我有工作，一个不是。这是工作的一个是少的想法，因为HTML是辅助函数内产生。我想不出就是为什么理想的是行不通的。

下面是工作之一：

  $ gridSummary.Column（OngoingDate
    标题：正在进行，
    格式：Html.DateTimeActionLink，
    风格：ongoingDate）公共静态对象DateTimeActionLink（此的HtmlHelper的HtmlHelper，动态项）
{
    约会时间？ linkDateTime = item.OngoingDate;
    如果（linkDateTime = NULL＆放大器;！＆安培; linkDateTime.HasValue）
    {
        VAR X = linkDateTime.Value.ToString（MM / DD / YYYY）;
        返回LinkExtensions.ActionLink（的HtmlHelper，X，编辑，MdsAsmtSectionQuestions，新的{mdsId = item.OngoingId}，NULL）;
    }    返回MvcHtmlString.Empty;
}
 

在这里是不正常的：

  $ gridSummary.Column（AssessmentInfo，标题：开放型| ARD
                        格式：（项目）=＆GT;
                        {
                            返回Html.DateTimeActionLink（
                                item.AssessmentDate，
                                MM / DD / YYYY
                                X =＆GT; Html.ActionLink（item.AssessmentInfo +|+ X编辑，MdsAsmtSectionQuestions，新的{mdsId = item.OngoingId}，NULL））;
                        }，
                        风格：assessmentInfo）    公共静态对象DateTimeActionLink（此的HtmlHelper的HtmlHelper，动态的项目，字符串格式，Func键＆LT;字符串，MvcHtmlString＆GT;的ActionLink）
    {
        可空＆LT;＆日期时间GT; linkDateTime =项目;        如果（linkDateTime = NULL＆放大器;！＆安培; linkDateTime.HasValue）
            返回的ActionLink（linkDateTime.Value.ToString（格式））;        返回MvcHtmlString.Empty;
    }
 

解决方案

的这一翻译：

  ...
格式：（项目）=＆GT;
                        {
                            返回Html.DateTimeActionLink（
                                item.AssessmentDate，
                                MM / DD / YYYY
                                X =＆GT; Html.ActionLink（item.AssessmentInfo +|+ X编辑，MdsAsmtSectionQuestions，新的{mdsId = item.OngoingId}，NULL））;
                        }
...
 

尝试：

  ...
格式：（项目）=＆GT;
                            Html.DateTimeActionLink（
                                    //添加投
                                    （可空＆LT;＆日期时间GT;）（item.AssessmentDate）
                                    MM / DD / YYYY
                                    //添加投
                                    X =＆GT; Html.ActionLink（（字符串）（item.AssessmentInfo）+|+ X编辑，MdsAsmtSectionQuestions，新的{mdsId = item.OngoingId}，NULL））;
...
 

I am trying to handle a case of a DateTime which might be null when rendering in a ASP.NET MVC3 WinGrid. I am getting an error when trying to set the WebGridColumn. I have one that I got working, one that isn't. The one that is working is less idea, for the html is generated within the helper function. What I cannot figure out is why the ideal one isn't working.

Here is the one that works:

$gridSummary.Column("OngoingDate", 
    header: "Ongoing", 
    format: Html.DateTimeActionLink, 
    style: "ongoingDate")

public static object DateTimeActionLink(this HtmlHelper htmlHelper, dynamic item)
{
    DateTime? linkDateTime = item.OngoingDate;
    if (linkDateTime != null && linkDateTime.HasValue)
    {
        var x = linkDateTime.Value.ToString("MM/dd/yyyy");
        return LinkExtensions.ActionLink(htmlHelper, x, "Edit", "MdsAsmtSectionQuestions", new { mdsId = item.OngoingId }, null);
    }

    return MvcHtmlString.Empty;
}       

here is the one that is not working:

    $gridSummary.Column("AssessmentInfo", header: "Open Type | ARD",
                        format: (item) =>
                        {
                            return Html.DateTimeActionLink(
                                item.AssessmentDate,
                                "MM/dd/yyyy",
                                x => Html.ActionLink(item.AssessmentInfo + " | " + x, "Edit", "MdsAsmtSectionQuestions", new { mdsId = item.OngoingId }, null));
                        },
                        style: "assessmentInfo")

    public static object DateTimeActionLink(this HtmlHelper htmlHelper, dynamic item, string format, Func<string, MvcHtmlString> actionLink)
    {
        Nullable<DateTime> linkDateTime = item;

        if (linkDateTime != null && linkDateTime.HasValue)
            return actionLink(linkDateTime.Value.ToString(format));

        return MvcHtmlString.Empty;
    }

解决方案

Intead of:

...
format: (item) =>
                        {
                            return Html.DateTimeActionLink(
                                item.AssessmentDate,
                                "MM/dd/yyyy",
                                x => Html.ActionLink(item.AssessmentInfo + " | " + x, "Edit", "MdsAsmtSectionQuestions", new { mdsId = item.OngoingId }, null));
                        }
...

Try:

...
format: (item) =>
                            Html.DateTimeActionLink(
                                    //added cast
                                    (Nullable<DateTime>)(item.AssessmentDate),
                                    "MM/dd/yyyy",
                                    //added cast
                                    x => Html.ActionLink((string)(item.AssessmentInfo) + " | " + x, "Edit", "MdsAsmtSectionQuestions", new { mdsId = item.OngoingId }, null));
...

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