ASP.NET MVC 模型绑定答案

【问题标题】：ASP.NET MVC Model BindingASP.NET MVC 模型绑定
【发布时间】：2009-06-17 23:34:44
【问题描述】：

我遇到了模型绑定问题。如果我确实在 CopyToModelStateDictionary 方法中使用前缀，我不会收到无效控件的样式或验证消息。如果我不使用前缀，我会收到样式和验证消息，但如果用户没有从动态创建的单选按钮列表中进行选择，页面会崩溃。我怎样才能得到两者？我不明白这里发生了什么。

    [AcceptVerbs(HttpVerbs.Post)]
    public ActionResult Edit(int id, FormCollection collection)
    {
        Request request = requestRepository.GetById(id);
        UpdateModel(request);
        Helpers.CopyToModelStateDictionary(request.GetRuleViolations(), ModelState, "request");
        ...
        if (!ModelState.IsValid) 
        {
            return View("Edit_Requestor", request);
        }
    }

    public static void CopyToModelStateDictionary(NameValueCollection errors, ModelStateDictionary modelState, string prefix)
    {
        foreach (string key in errors)
        {
            foreach (string value in errors.GetValues(key))
            {
                modelState.AddModelError(prefix + "." + key, value);
            }
        }
    }

错误信息

Line 9:   foreach (ProblemType problemType in problemTypes)
Line 10:  {
Line 11:      Writer.Write(Html.RadioButton("ProblemType", problemType.Value));
Line 12:      Writer.Write(problemType.Text + "<br/>");
Line 13:  }

堆栈跟踪：

[NullReferenceException: Object reference not set to an instance of an object.]
System.Web.Mvc.HtmlHelper.GetModelStateValue(String key, Type destinationType) +63
System.Web.Mvc.Html.InputExtensions.InputHelper(HtmlHelper htmlHelper, InputType inputType, String name, Object value, Boolean useViewData, Boolean isChecked, Boolean setId, Boolean isExplicitValue, IDictionary`2 htmlAttributes) +328
System.Web.Mvc.Html.InputExtensions.RadioButton(HtmlHelper htmlHelper, String name, Object value, Boolean isChecked, IDictionary`2 htmlAttributes) +193
System.Web.Mvc.Html.InputExtensions.RadioButton(HtmlHelper htmlHelper, String name, Object value, IDictionary`2 htmlAttributes) +282
System.Web.Mvc.Html.InputExtensions.RadioButton(HtmlHelper htmlHelper, String name, Object value) +61
ASP.views_request_lstproblemtype_ascx.__Render__control1(HtmlTextWriter __w, Control parameterContainer) in c:\Web\Views\Request\lstProblemType.ascx:11
System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +256
System.Web.UI.Control.RenderChildren(HtmlTextWriter writer) +19
System.Web.UI.Control.Render(HtmlTextWriter writer) +10
System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +27
System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter) +99
System.Web.UI.Control.RenderControl(HtmlTextWriter writer) +25
System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +134
System.Web.UI.Control.RenderChildren(HtmlTextWriter writer) +19
System.Web.UI.Page.Render(HtmlTextWriter writer) +29
System.Web.Mvc.ViewPage.Render(HtmlTextWriter writer) +59
System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +27
System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter) +99
System.Web.UI.Control.RenderControl(HtmlTextWriter writer) +25
System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +1266

感谢您阅读我的问题！

【问题讨论】：

标签： c# asp.net-mvc model-binding

【解决方案1】：

这可能会有所帮助。

您正在添加一个模态错误，因此 MVC 正在尝试检索尝试的值，但由于您没有添加它，所以它失败了。

Validating form using ModelState

ASP.NET MVC - Html.Textbox() throws "Object reference not set to an instance of an object"

【讨论】：

感谢这些链接。在发布我的解决方案之前，我必须进行更多研究。
这些链接很有帮助。此外，如果有人需要更多帮助，请在 StackOverflow 中搜索“ValueProvider”。在进行更多测试后，我将使用我的解决方案进行编辑。