MVC2中出现一个相同的键已被添加的问题原因

最新推荐文章于 2025-09-11 02:19:05 发布

原创最新推荐文章于 2025-09-11 02:19:05 发布 · 8.8k 阅读

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在使用MVC2开发时，遇到'An item with the same key has already been added.'错误，原因是实体类中存在大小写不同的同名属性。在Request.Form中，键值不区分大小写导致重复。解决方法是避免大小写不一致的同名属性。

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这两天用MVC2搞了一个软件，结果今天调试时碰到一个很头疼的问题。

只要使用HtmlHelper的控件模版在界面上显示控件,如下：

<%=Html.HiddenFor(m => m.ID)%>

就报出An item with the same key has already been added这个错误。

后来在国外网站上才查到一个老兄也碰到这个问题，原因是对应的实体中有重名的属性。

像我这里 UserInfo实体类中有一个"ID"属性，这个实体类继承自EntityBase类，基类中有一个属性"Id".

注意这里的两个属性大小写不同，C#会认为是两个属性，但是在MVC的Request.Form中Key值是不区分大小写的。

这样就会出现添加重复键值的错误。

这个错误很少发生，因为如果大小写相同它也会被认为是一个属性，只有大小写不同时才会发生。

An item with the same key has already been added.

Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.ArgumentException: An item with the same key has already been added.

Source Error:

An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.

Stack Trace:


[ArgumentException: An item with the same key has already been added.]
   System.ThrowHelper.ThrowArgumentException(ExceptionResource resource) +52
   System.Collections.Generic.Dictionary`2.Insert(TKey key, TValue value, Boolean add) +9383019
   System.Linq.Enumerable.ToDictionary(IEnumerable`1 source, Func`2 keySelector, Func`2 elementSelector, IEqualityComparer`1 comparer) +252
   System.Linq.Enumerable.ToDictionary(IEnumerable`1 source, Func`2 keySelector, IEqualityComparer`1 comparer) +91
   System.Web.Mvc.ModelBindingContext.get_PropertyMetadata() +228
   System.Web.Mvc.DefaultModelBinder.BindProperty(ControllerContext controllerContext, ModelBindingContext bindingContext, PropertyDescriptor propertyDescriptor) +392
   System.Web.Mvc.DefaultModelBinder.BindProperties(ControllerContext controllerContext, ModelBindingContext bindingContext) +147
   System.Web.Mvc.DefaultModelBinder.BindComplexElementalModel(ControllerContext controllerContext, ModelBindingContext bindingContext, Object model) +98
   System.Web.Mvc.DefaultModelBinder.BindComplexModel(ControllerContext controllerContext, ModelBindingContext bindingContext) +2503
   System.Web.Mvc.DefaultModelBinder.BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext) +548
   System.Web.Mvc.ControllerActionInvoker.GetParameterValue(ControllerContext controllerContext, ParameterDescriptor parameterDescriptor) +474
   System.Web.Mvc.ControllerActionInvoker.GetParameterValues(ControllerContext controllerContext, ActionDescriptor actionDescriptor) +181
   System.Web.Mvc.ControllerActionInvoker.InvokeAction(ControllerContext controllerContext, String actionName) +830
   System.Web.Mvc.Controller.ExecuteCore() +136
   System.Web.Mvc.ControllerBase.Execute(RequestContext requestContext) +111
   System.Web.Mvc.ControllerBase.System.Web.Mvc.IController.Execute(RequestContext requestContext) +39
   System.Web.Mvc.<>c__DisplayClass8.<BeginProcessRequest>b__4() +65
   System.Web.Mvc.Async.<>c__DisplayClass1.<MakeVoidDelegate>b__0() +44
   System.Web.Mvc.Async.<>c__DisplayClass8`1.<BeginSynchronous>b__7(IAsyncResult _) +42
   System.Web.Mvc.Async.WrappedAsyncResult`1.End() +141
   System.Web.Mvc.Async.AsyncResultWrapper.End(IAsyncResult asyncResult, Object tag) +54
   System.Web.Mvc.Async.AsyncResultWrapper.End(IAsyncResult asyncResult, Object tag) +40
   System.Web.Mvc.MvcHandler.EndProcessRequest(IAsyncResult asyncResult) +52
   System.Web.Mvc.MvcHandler.System.Web.IHttpAsyncHandler.EndProcessRequest(IAsyncResult result) +38
   System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +8836977
   System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +184

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