向上错误提示
{"success":false,"code":500,"count":0,"data":null,"msg":"System.NullReferenceException:Object reference not set to an instance of an object.\r\n at Microsoft.AspNetCore.Mvc.Rendering.MultiSelectList.GetListItemsWithValueField()\r\n at Microsoft.AspNetCore.Mvc.Rendering.MultiSelectList.GetListItems()\r\n at Microsoft.AspNetCore.Mvc.Rendering.MultiSelectList.GetEnumerator()\r\n at System.Collections.Generic.List`1..ctor(IEnumerable`1 collection)\r\n at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)\r\n at Microsoft.AspNetCore.Mvc.ViewFeatures.DefaultHtmlGenerator.GenerateGroupsAndOptions(String optionLabel, IEnumerable`1 selectList, ICollection`1 currentValues)\r\n at Microsoft.AspNetCore.Mvc.ViewFeatures.DefaultHtmlGenerator.GenerateGroupsAndOptions(String optionLabel, IEnumerable`1 selectList)\r\n at Microsoft.AspNetCore.Mvc.TagHelpers.SelectTagHelper.Process(TagHelperContext context, TagHelperOutput output)\r\n at Microsoft.AspNetCore.Razor.TagHelpers.TagHelper.ProcessAsync(TagHelperContext context, TagHelperOutput output)\r\n at Microsoft.AspNetCore.Razor.Runtime.TagHelpers.TagHelperRunner.RunAsync(TagHelperExecutionContext executionContext)\r\n at AspNetCore.Areas_Manager_Views_Brand_Add.<ExecuteAsync>b__24_1() in E:\\*****\\Dis.WebAdmin\\Dis.WebAdmin\\Areas\\Manager\\Views\\Brand\\Add.cshtml:line 51\r\n at Microsoft.AspNetCore.Razor.Runtime.TagHelpers.TagHelperExecutionContext.GetChildContentAsync(Boolean useCachedResult, HtmlEncoder encoder)\r\n at Microsoft.AspNetCore.Mvc.TagHelpers.RenderAtEndOfFormTagHelper.ProcessAsync(TagHelperContext context, TagHelperOutput output)\r\nat Microsoft.AspNetCore.Razor.Runtime.TagHelpers.TagHelperRunner.<RunAsync>g__Awaited|0_0(Task task, TagHelperExecutionContext executionContext, Int32 i, Int32 count)\r\n at AspNetCore.Areas_Manager_Views_Brand_Add.ExecuteAsync() in E:\\****\\Dis.WebAdmin\\Dis.WebAdmin\\Areas\\Manager\\Views\\Brand\\Add.cshtml:line 3\r\n at Microsoft.AspNetCore.Mvc.Razor.RazorView.RenderPageCoreAsync(IRazorPage page, ViewContext context)\r\n at Microsoft.AspNetCore.Mvc.Razor.RazorView.RenderPageAsync(IRazorPage page, ViewContext context, Boolean invokeViewStarts)\r\n at Microsoft.AspNetCore.Mvc.Razor.RazorView.RenderAsync(ViewContext context)\r\n at Microsoft.AspNetCore.Mvc.ViewFeatures.ViewExecutor.ExecuteAsync(ViewContext viewContext, String contentType, Nullable`1 statusCode)\r\nat Microsoft.AspNetCore.Mvc.ViewFeatures.ViewExecutor.ExecuteAsync(ViewContext viewContext, String contentType, Nullable`1 statusCode)\r\n at Microsoft.AspNetCore.Mvc.ViewFeatures.ViewExecutor.ExecuteAsync(ActionContext actionContext, IView view, ViewDataDictionary viewData, ITempDataDictionary tempData, String contentType, Nullable`1 statusCode)\r\n at Microsoft.AspNetCore.Mvc.ViewFeatures.ViewResultExecutor.ExecuteAsync(ActionContext context, ViewResult result)\r\n at Microsoft.AspNetCore.Mvc.ViewResult.ExecuteResultAsync(ActionContext context)\r\n at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeNextResultFilterAsync>g__Awaited|29_0[TFilter,TFilterAsync](ResourceInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)\r\n at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.Rethrow(ResultExecutedContextSealed context)\r\n at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.ResultNext[TFilter,TFilterAsync](State& next, Scope& scope, Object& state, Boolean& isCompleted)\r\n at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.InvokeResultFilters()\r\n--- End of stack trace from previous location where exception was thrown ---\r\n at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeNextResourceFilter>g__Awaited|24_0(ResourceInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)\r\n at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.Rethrow(ResourceExecutedContextSealed context)\r\n at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted)\r\n at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.InvokeFilterPipelineAsync()\r\n--- End of stack trace from previous location where exception was thrown ---\r\nat Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeAsync>g__Awaited|17_0(ResourceInvoker invoker, Task task, IDisposable scope)\r\n at Microsoft.AspNetCore.Routing.EndpointMiddleware.<Invoke>g__AwaitRequestTask|6_0(Endpoint endpoint, Task requestTask, ILogger logger)\r\n at Microsoft.AspNetCore.Session.SessionMiddleware.Invoke(HttpContext context)\r\n at Microsoft.AspNetCore.Session.SessionMiddleware.Invoke(HttpContext context)\r\n at Microsoft.AspNetCore.Authorization.AuthorizationMiddleware.Invoke(HttpContext context)\r\nat Microsoft.AspNetCore.Authentication.AuthenticationMiddleware.Invoke(HttpContext context)\r\n at Dis.Components.ExceptionMiddleware.Invoke(HttpContext context) in E:\\***\\Dis.WebAdmin\\Dis.Components\\Exception\\ExceptionMiddleware.cs:line 38"}报第3行和第51行错误
看下文件
@{ViewData["Title"] = "添加品牌";Layout = "~/Areas/Manager/Views/Shared/_Layout.cshtml";
}第三行提示的是ViewData
<div class="layui-form-item"><label class="layui-form-label">*****/label><div class="layui-input-inline" style="width: 200px;"><select name="Supervisor" asp-items="@ViewBag.SupervisorList" lay-filter="Supervisor" lay-search><option value="">请选择</option></select></div></div>第51行 显示的是这个ViewBag
开始百度了，我一度怀疑我的viewbag因为数据是null出现了问题，但是为啥其他的是null没问题，
然后考虑要把这个viewbag改成ViewData
失败，跟本不允许这么写，因为类型就错误了，编译错误。
开始进行后台查询数据的数据对比，
/// <summary>/// 视图/// </summary>/// <returns></returns>public IActionResult Add(){//List<Dis.Entity.RiderMaster> list = _rider.GetList();//训练督导List<Dis.Entity.RiderMaster> SupervisorList = list.FindAll(s => s.Position == "P03");//List<Dis.Entity.RiderMaster> OperationsDirectorList = list.FindAll(s => s.Position == "P04");//List<Dis.Entity.RiderMaster> GeneralManagerList = list.FindAll(s => s.Position == "P05");//ViewBag.CompanyList = new MultiSelectList(_organization.GetCompany(Client,"1"), "Id", "Name");ViewBag.SupervisorList = new MultiSelectList(SupervisorList, "IRiderIdD", "RederName");ViewBag.OperationsDirectorList = new MultiSelectList(OperationsDirectorList, "RiderId", "RederName");ViewBag.GeneralManagerList = new MultiSelectList(GeneralManagerList, "RiderId", "RederName");return View();}感觉没啥问题，继续百度，
结果无意间发现，
ViewBag.SupervisorList = new MultiSelectList(SupervisorList, "IRiderIdD", "RederName");
看到没 ，这个地方多了一个D ，可能是无意间按到了键盘搞错了，
问题解决了