C# Razor helper中出现奇怪的NullReferenceException异常

我在C#Web表单应用程序中使用Razor助手

调用时，以下代码编译并呈现A-OK：

@helper MemberListItem(string firstname, string lastname, string avatarUrl)
{
    <li>
        @firstname @lastname
        @avatarUrl
    </li>
}

@helper MemberListItem(string firstname, string lastname, string avatarUrl)
{
    <li>
        @firstname @lastname
        <img src="@avatarUrl"/>
    </li>
}

请记住，除了帮助器中的

@avatarUrl

位置之外，我没有改变任何东西

如何显示图像

更新1: 我还尝试将我的

img

代码包装在

中（无效）：

这不会（NullReferenceException）：

编译代码（来自c:\Windows中的临时ASP.NET文件）：

#pragma checksum“C:\Users\Public\Documents\VisualStudioProjects\OnlineStable\Aqha\App_code\RazorHelpers\IdentityProvider.cshtml”{ff1816ec-aa5e-4d10-87f7-6F49638333460}“46B0FEE2042706017F4AE53D4EA612F3E73EDF8B”
//------------------------------------------------------------------------------
// 
//这段代码是由一个工具生成的。
//运行时版本：4.0.30319.18052
//
//对此文件的更改可能会导致不正确的行为，如果
//重新生成代码。
// 
//------------------------------------------------------------------------------
命名空间ASP.RazorHelpers{
使用制度；
使用System.Collections.Generic；
使用System.IO；
使用System.Linq；
Net系统；
使用System.Web；
使用System.Web.Helpers；
使用System.Web.Security；
使用System.Web.UI；
使用System.Web.Web网页；
使用System.Web.WebPages.Html；
#第1行“C:\Users\Public\Documents\VisualStudioProjects\OnlineStable\Aqha\App_Code\RazorHelpers\IdentityProvider.cshtml”
使用Aqha.DatabaseHelpers；
#行默认值
#隐藏线
#第2行“C:\Users\Public\Documents\VisualStudioProjects\OnlineStable\Aqha\App_Code\RazorHelpers\IdentityProvider.cshtml”
使用Aqha.RazorExtensions；
#行默认值
#隐藏线
#第3行“C:\Users\Public\Documents\VisualStudioProjects\OnlineStable\Aqha\App_Code\RazorHelpers\IdentityProvider.cshtml”
使用DevExpress.Utils.Drawing.Helpers；
#行默认值
#隐藏线
公共类标识提供程序：System.Web.WebPages.HelperPage{
#隐藏线
#第5行“C:\Users\Public\Documents\VisualStudioProjects\OnlineStable\Aqha\App_Code\RazorHelpers\IdentityProvider.cshtml”
public static System.Web.WebPages.HelperResult ListGroupGrid（IEnumerable提供程序）{
#行默认值
#隐藏线
返回新的System.Web.WebPages.HelperResult（\uuu razor\uHelper\uWriter=>{
#第5行“C:\Users\Public\Documents\VisualStudioProjects\OnlineStable\Aqha\App_Code\RazorHelpers\IdentityProvider.cshtml”
#行默认值
#隐藏线
BeginContext（uu razor\u helper\u writer，“~/App\u Code/razor helpers/IdentityProvider.cshtml”，202,11，true）；
WriteLiteralTo（\r\n）；
EndContext（uu razor\u helper\u writer，“~/App\u Code/razor helpers/IdentityProvider.cshtml”，202,11，true）；
#第7行“C:\Users\Public\Documents\VisualStudioProjects\OnlineStable\Aqha\App_Code\RazorHelpers\IdentityProvider.cshtml”
#行默认值
#隐藏线
#第7行“C:\Users\Public\Documents\VisualStudioProjects\OnlineStable\Aqha\App_Code\RazorHelpers\IdentityProvider.cshtml”
foreach（提供程序中的var提供程序）{
#行默认值
#隐藏线
BeginContext（uu razor\u helper\u writer，“~/App\u Code/razor helpers/IdentityProvider.cshtml”，272,13，false）；
#第8行“C:\Users\Public\Documents\VisualStudioProjects\OnlineStable\Aqha\App_Code\RazorHelpers\IdentityProvider.cshtml”
WriteTo（\uuuRazor\uHelper\uWriter，provider.Name）；
#行默认值
#隐藏线
EndContext（uu razor\u helper\u writer，“~/App\u Code/razor helpers/IdentityProvider.cshtml”，272,13，false）；
#第8行“C:\Users\Public\Documents\VisualStudioProjects\OnlineStable\Aqha\App_Code\RazorHelpers\IdentityProvider.cshtml”
#行默认值
#隐藏线
BeginContext（uu razor\u helper\u writer，“~/App\u Code/razor helpers/IdentityProvider.cshtml”，287,16，true）；
WriteEletrato（\uuuRazor\uHelper\uWriter，”（provider.IconUrl
#行默认值
#隐藏线
，309），假）
);
BeginContext（uu razor\u helper\u writer，“~/App\u Code/razor helpers/IdentityProvider.cshtml”，327,4，true）；
WriteLiteralTo（\uuuRazor\uHelper\uWriter，“/>\r\n”）；
EndContext（uu razor\u helper\u writer，“~/App\u Code/RazorHelpers/IdentityProvider.cshtml”，327,4，true）；
#第10行“C:\Users\Public\Documents\VisualStudioProjects\OnlineStable\Aqha\App_Code\RazorHelpers\IdentityProvider.cshtml”
}
#行默认值
#隐藏线
BeginContext（uu razor\u helper\u writer，“~/App\u Code/razor helpers/IdentityProvider.cshtml”，342,12，true）；
WriteLiteralTo（\r\n）；
EndContext（uu razor\u helper\u writer，“~/App\u Code/RazorHelpers/IdentityProvider.cshtml”，342,12，true）；
#第12行“C:\Users\Public\Documents\VisualStudioProjects\OnlineStable\Aqha\App_Code\RazorHelpers\IdentityProvider.cshtml”
#行默认值
#隐藏线
});
#第12行“C:\Users\Public\Documents\VisualStudioProjects\OnlineStable\Aqha\App_Code\RazorHelpers\IdentityProvider.cshtml”
}
#行默认值
#隐藏线
公共标识提供程序（）{
}
受保护的静态ASP.global\U asax应用程序实例{
得到{
返回（（ASP.global_asax）（Context.ApplicationInstance））；
}
}
}
}

更新5: 我做了更多的测试。为了尽可能清楚地说明这个问题，我删除了所有的输入参数和额外的标记

考虑以下三个助手：

#pragma checksum "C:\Users\Public\Documents\VisualStudioProjects\OnlineStable\Aqha\App_Code\RazorHelpers\IdentityProvider.cshtml" "{ff1816ec-aa5e-4d10-87f7-6f4963833460}" "46B0FEE2042706017F4AE53D4EA612F3E73EDF8B"
//------------------------------------------------------------------------------
// <auto-generated>
//     This code was generated by a tool.
//     Runtime Version:4.0.30319.18052
//
//     Changes to this file may cause incorrect behavior and will be lost if
//     the code is regenerated.
// </auto-generated>
//------------------------------------------------------------------------------

namespace ASP.RazorHelpers {
    using System;
    using System.Collections.Generic;
    using System.IO;
    using System.Linq;
    using System.Net;
    using System.Web;
    using System.Web.Helpers;
    using System.Web.Security;
    using System.Web.UI;
    using System.Web.WebPages;
    using System.Web.WebPages.Html;

    #line 1 "C:\Users\Public\Documents\VisualStudioProjects\OnlineStable\Aqha\App_Code\RazorHelpers\IdentityProvider.cshtml"
    using Aqha.DatabaseHelpers;

    #line default
    #line hidden

    #line 2 "C:\Users\Public\Documents\VisualStudioProjects\OnlineStable\Aqha\App_Code\RazorHelpers\IdentityProvider.cshtml"
    using Aqha.RazorExtensions;

    #line default
    #line hidden

    #line 3 "C:\Users\Public\Documents\VisualStudioProjects\OnlineStable\Aqha\App_Code\RazorHelpers\IdentityProvider.cshtml"
    using DevExpress.Utils.Drawing.Helpers;

    #line default
    #line hidden


    public class IdentityProvider : System.Web.WebPages.HelperPage {

#line hidden

#line 5 "C:\Users\Public\Documents\VisualStudioProjects\OnlineStable\Aqha\App_Code\RazorHelpers\IdentityProvider.cshtml"
public static System.Web.WebPages.HelperResult ListGroupGrid(IEnumerable<IdentityProviderData.ExternalIdentityProvider> providers) {
#line default
#line hidden
return new System.Web.WebPages.HelperResult(__razor_helper_writer => {

#line 5 "C:\Users\Public\Documents\VisualStudioProjects\OnlineStable\Aqha\App_Code\RazorHelpers\IdentityProvider.cshtml"



#line default
#line hidden
BeginContext(__razor_helper_writer, "~/App_Code/RazorHelpers/IdentityProvider.cshtml", 202, 11, true);

WriteLiteralTo(__razor_helper_writer, "    <div>\r\n");

EndContext(__razor_helper_writer, "~/App_Code/RazorHelpers/IdentityProvider.cshtml", 202, 11, true);


#line 7 "C:\Users\Public\Documents\VisualStudioProjects\OnlineStable\Aqha\App_Code\RazorHelpers\IdentityProvider.cshtml"


#line default
#line hidden

#line 7 "C:\Users\Public\Documents\VisualStudioProjects\OnlineStable\Aqha\App_Code\RazorHelpers\IdentityProvider.cshtml"
         foreach(var provider in providers){


#line default
#line hidden
BeginContext(__razor_helper_writer, "~/App_Code/RazorHelpers/IdentityProvider.cshtml", 272, 13, false);


#line 8 "C:\Users\Public\Documents\VisualStudioProjects\OnlineStable\Aqha\App_Code\RazorHelpers\IdentityProvider.cshtml"
WriteTo(__razor_helper_writer, provider.Name);


#line default
#line hidden
EndContext(__razor_helper_writer, "~/App_Code/RazorHelpers/IdentityProvider.cshtml", 272, 13, false);


#line 8 "C:\Users\Public\Documents\VisualStudioProjects\OnlineStable\Aqha\App_Code\RazorHelpers\IdentityProvider.cshtml"



#line default
#line hidden
BeginContext(__razor_helper_writer, "~/App_Code/RazorHelpers/IdentityProvider.cshtml", 287, 16, true);

WriteLiteralTo(__razor_helper_writer, "            <img");

EndContext(__razor_helper_writer, "~/App_Code/RazorHelpers/IdentityProvider.cshtml", 287, 16, true);

WriteAttributeTo(__razor_helper_writer, "src", Tuple.Create(" src=\"", 303), Tuple.Create("\"", 326)

#line 9 "C:\Users\Public\Documents\VisualStudioProjects\OnlineStable\Aqha\App_Code\RazorHelpers\IdentityProvider.cshtml"
, Tuple.Create(Tuple.Create("", 309), Tuple.Create<System.Object, System.Int32>(provider.IconUrl

#line default
#line hidden
, 309), false)
);

BeginContext(__razor_helper_writer, "~/App_Code/RazorHelpers/IdentityProvider.cshtml", 327, 4, true);

WriteLiteralTo(__razor_helper_writer, "/>\r\n");

EndContext(__razor_helper_writer, "~/App_Code/RazorHelpers/IdentityProvider.cshtml", 327, 4, true);


#line 10 "C:\Users\Public\Documents\VisualStudioProjects\OnlineStable\Aqha\App_Code\RazorHelpers\IdentityProvider.cshtml"
        }


#line default
#line hidden
BeginContext(__razor_helper_writer, "~/App_Code/RazorHelpers/IdentityProvider.cshtml", 342, 12, true);

WriteLiteralTo(__razor_helper_writer, "    </div>\r\n");

EndContext(__razor_helper_writer, "~/App_Code/RazorHelpers/IdentityProvider.cshtml", 342, 12, true);


#line 12 "C:\Users\Public\Documents\VisualStudioProjects\OnlineStable\Aqha\App_Code\RazorHelpers\IdentityProvider.cshtml"


#line default
#line hidden
});

#line 12 "C:\Users\Public\Documents\VisualStudioProjects\OnlineStable\Aqha\App_Code\RazorHelpers\IdentityProvider.cshtml"
}
#line default
#line hidden


        public IdentityProvider() {
        }

        protected static ASP.global_asax ApplicationInstance {
            get {
                return ((ASP.global_asax)(Context.ApplicationInstance));
            }
        }
    }
}

@helper BaseCase（）{
}
@helper VariableBaseCase（）{
var src=“/Resources/Images/Placeholders/generic user image.jpg”；
来源是@src
}
@辅助变量（）{
var src=“/Resources/Images/Placeholders/generic user image.jpg”；
来源是@src
}

当我从ASPX调用前两个助手时，它们毫无例外地显示输出（图像正常显示）：

@helper BaseCase() {
    <img src="/Resources/Images/Placeholders/generic-user-image.jpg"/>
}

@helper VariableBaseCase() {
    var src = "/Resources/Images/Placeholders/generic-user-image.jpg";
    <img src="/Resources/Images/Placeholders/generic-user-image.jpg"/>
    <text>the source is @src</text>
}

@helper Variable() {
    var src = "/Resources/Images/Placeholders/generic-user-image.jpg";
    <img src="@src"/>
    <text>the source is @src</text>
}

当我调用最后一个助手时，我得到的错误与我一直得到的错误相同

<%= RazorHelpers.ImageTest.BaseCase().ToString() %>
<%= RazorHelpers.ImageTest.VariableBaseCase().ToString() %>

我希望现在我正确地相信这是一条相对的道路

<%= @HelperFile.Helper(parameters).ToString() %>

<img src="/Resources/Images/Placeholders/generic-user-image.jpg"/>

<img src="~/Resources/Images/Placeholders/generic-user-image.jpg"/>

<img src="@avatarUrl"/>

<img src="~@avatarUrl"/>

@helper ListGroupGrid(IEnumerable<ExternalIdentityProvider> providers) {
    <div>
        @foreach(var provider in providers){
            @provider.Name
            <img src="@provider.IconUrl"/>
        }
    </div>
}

#pragma checksum "C:\Users\Public\Documents\VisualStudioProjects\OnlineStable\Aqha\App_Code\RazorHelpers\IdentityProvider.cshtml" "{ff1816ec-aa5e-4d10-87f7-6f4963833460}" "46B0FEE2042706017F4AE53D4EA612F3E73EDF8B"
//------------------------------------------------------------------------------
// <auto-generated>
//     This code was generated by a tool.
//     Runtime Version:4.0.30319.18052
//
//     Changes to this file may cause incorrect behavior and will be lost if
//     the code is regenerated.
// </auto-generated>
//------------------------------------------------------------------------------

namespace ASP.RazorHelpers {
    using System;
    using System.Collections.Generic;
    using System.IO;
    using System.Linq;
    using System.Net;
    using System.Web;
    using System.Web.Helpers;
    using System.Web.Security;
    using System.Web.UI;
    using System.Web.WebPages;
    using System.Web.WebPages.Html;

    #line 1 "C:\Users\Public\Documents\VisualStudioProjects\OnlineStable\Aqha\App_Code\RazorHelpers\IdentityProvider.cshtml"
    using Aqha.DatabaseHelpers;

    #line default
    #line hidden

    #line 2 "C:\Users\Public\Documents\VisualStudioProjects\OnlineStable\Aqha\App_Code\RazorHelpers\IdentityProvider.cshtml"
    using Aqha.RazorExtensions;

    #line default
    #line hidden

    #line 3 "C:\Users\Public\Documents\VisualStudioProjects\OnlineStable\Aqha\App_Code\RazorHelpers\IdentityProvider.cshtml"
    using DevExpress.Utils.Drawing.Helpers;

    #line default
    #line hidden


    public class IdentityProvider : System.Web.WebPages.HelperPage {

#line hidden

#line 5 "C:\Users\Public\Documents\VisualStudioProjects\OnlineStable\Aqha\App_Code\RazorHelpers\IdentityProvider.cshtml"
public static System.Web.WebPages.HelperResult ListGroupGrid(IEnumerable<IdentityProviderData.ExternalIdentityProvider> providers) {
#line default
#line hidden
return new System.Web.WebPages.HelperResult(__razor_helper_writer => {

#line 5 "C:\Users\Public\Documents\VisualStudioProjects\OnlineStable\Aqha\App_Code\RazorHelpers\IdentityProvider.cshtml"



#line default
#line hidden
BeginContext(__razor_helper_writer, "~/App_Code/RazorHelpers/IdentityProvider.cshtml", 202, 11, true);

WriteLiteralTo(__razor_helper_writer, "    <div>\r\n");

EndContext(__razor_helper_writer, "~/App_Code/RazorHelpers/IdentityProvider.cshtml", 202, 11, true);


#line 7 "C:\Users\Public\Documents\VisualStudioProjects\OnlineStable\Aqha\App_Code\RazorHelpers\IdentityProvider.cshtml"


#line default
#line hidden

#line 7 "C:\Users\Public\Documents\VisualStudioProjects\OnlineStable\Aqha\App_Code\RazorHelpers\IdentityProvider.cshtml"
         foreach(var provider in providers){


#line default
#line hidden
BeginContext(__razor_helper_writer, "~/App_Code/RazorHelpers/IdentityProvider.cshtml", 272, 13, false);


#line 8 "C:\Users\Public\Documents\VisualStudioProjects\OnlineStable\Aqha\App_Code\RazorHelpers\IdentityProvider.cshtml"
WriteTo(__razor_helper_writer, provider.Name);


#line default
#line hidden
EndContext(__razor_helper_writer, "~/App_Code/RazorHelpers/IdentityProvider.cshtml", 272, 13, false);


#line 8 "C:\Users\Public\Documents\VisualStudioProjects\OnlineStable\Aqha\App_Code\RazorHelpers\IdentityProvider.cshtml"



#line default
#line hidden
BeginContext(__razor_helper_writer, "~/App_Code/RazorHelpers/IdentityProvider.cshtml", 287, 16, true);

WriteLiteralTo(__razor_helper_writer, "            <img");

EndContext(__razor_helper_writer, "~/App_Code/RazorHelpers/IdentityProvider.cshtml", 287, 16, true);

WriteAttributeTo(__razor_helper_writer, "src", Tuple.Create(" src=\"", 303), Tuple.Create("\"", 326)

#line 9 "C:\Users\Public\Documents\VisualStudioProjects\OnlineStable\Aqha\App_Code\RazorHelpers\IdentityProvider.cshtml"
, Tuple.Create(Tuple.Create("", 309), Tuple.Create<System.Object, System.Int32>(provider.IconUrl

#line default
#line hidden
, 309), false)
);

BeginContext(__razor_helper_writer, "~/App_Code/RazorHelpers/IdentityProvider.cshtml", 327, 4, true);

WriteLiteralTo(__razor_helper_writer, "/>\r\n");

EndContext(__razor_helper_writer, "~/App_Code/RazorHelpers/IdentityProvider.cshtml", 327, 4, true);


#line 10 "C:\Users\Public\Documents\VisualStudioProjects\OnlineStable\Aqha\App_Code\RazorHelpers\IdentityProvider.cshtml"
        }


#line default
#line hidden
BeginContext(__razor_helper_writer, "~/App_Code/RazorHelpers/IdentityProvider.cshtml", 342, 12, true);

WriteLiteralTo(__razor_helper_writer, "    </div>\r\n");

EndContext(__razor_helper_writer, "~/App_Code/RazorHelpers/IdentityProvider.cshtml", 342, 12, true);


#line 12 "C:\Users\Public\Documents\VisualStudioProjects\OnlineStable\Aqha\App_Code\RazorHelpers\IdentityProvider.cshtml"


#line default
#line hidden
});

#line 12 "C:\Users\Public\Documents\VisualStudioProjects\OnlineStable\Aqha\App_Code\RazorHelpers\IdentityProvider.cshtml"
}
#line default
#line hidden


        public IdentityProvider() {
        }

        protected static ASP.global_asax ApplicationInstance {
            get {
                return ((ASP.global_asax)(Context.ApplicationInstance));
            }
        }
    }
}

@helper BaseCase() {
    <img src="/Resources/Images/Placeholders/generic-user-image.jpg"/>
}

@helper VariableBaseCase() {
    var src = "/Resources/Images/Placeholders/generic-user-image.jpg";
    <img src="/Resources/Images/Placeholders/generic-user-image.jpg"/>
    <text>the source is @src</text>
}

@helper Variable() {
    var src = "/Resources/Images/Placeholders/generic-user-image.jpg";
    <img src="@src"/>
    <text>the source is @src</text>
}

<%= RazorHelpers.ImageTest.BaseCase().ToString() %>
<%= RazorHelpers.ImageTest.VariableBaseCase().ToString() %>

<%= RazorHelpers.ImageTest.Variable().ToString() %>

@helper MemberListItem(string firstname, string lastname, string avatarUrl)
{
    <li>
        @(firstname) @(lastname)
        <img src="@(avatarUrl)" />
    </li>
}

<input name="ItemUID" type="hidden" value="@ItemUID" />

<input name="ItemUID" type="hidden" @("value=")"@ItemUID" />

string attributeValue= "some value";

string attributeExpression= "attributeName=" + attributeValue;

<div class="" id="" @attributeExpression></div>