话说我有一个action:
public void SaveTask(Guid id, string title, bool? isPublic)
准备让它接收"CreateTask"和"EditTask"创建的表单:
<form action="SaveTask" method="post">
<dl>
<dt>标题</dt>
<dd><input type="text" value="" size="20" name="title" id="title" /></dd>
<dt>公开</dt>
<dd><input type="checkbox" value="true" name="isPublic" /> true</dd>
</dl>
<input type="hidden" value="00000000-0000-0000-0000-000000000000" name="id" id="id" />
<input type="submit" value="创建任务" name="submit" id="submit" />
</form>但是每次提交表单,都会出现异常:
[FormatException: GUID 应包含带 4 个短划线的 32 位数(xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx)。]
System.Guid..ctor(String g) +2284
System.ComponentModel.GuidConverter.ConvertFrom(ITypeDescriptorContext context, CultureInfo culture, Object value) +103
System.ComponentModel.TypeConverter.ConvertFrom(Object value) +54
System.Web.Mvc.Controller.ConvertParameterType(Object value, Type destinationType, String parameterName, String actionName) +161
[InvalidOperationException: Cannot convert parameter 'id' in action 'SaveTask' with value '' to type 'System.Guid'.]
System.Web.Mvc.Controller.ConvertParameterType(Object value, Type destinationType, String parameterName, String actionName) +301
System.Web.Mvc.Controller.InvokeActionMethod(MethodInfo methodInfo, RouteValueDictionary values) +760
[InvalidOperationException: A value is required for parameter 'id' in action 'SaveTask'. The parameter either has no value or its value could not be converted. To make a parameter optional its type should either be a reference type or a Nullable type.]
System.Web.Mvc.Controller.InvokeActionMethod(MethodInfo methodInfo, RouteValueDictionary values) +902
System.Web.Mvc.Controller.InvokeAction(String actionName, RouteValueDictionary values) +263
System.Web.Mvc.Controller.Execute(ControllerContext controllerContext) +161
System.Web.Mvc.Controller.System.Web.Mvc.IController.Execute(ControllerContext controllerContext) +4
System.Web.Mvc.MvcHandler.ProcessRequest(HttpContextBase httpContext) +212
System.Web.Mvc.MvcHandler.ProcessRequest(HttpContext httpContext) +36
System.Web.Mvc.MvcHandler.System.Web.IHttpHandler.ProcessRequest(HttpContext httpContext) +4
System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +358
System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +64
注意加下划线的部分:不是明明有回传的值"
00000000-0000-0000-0000-000000000000"吗,怎么变成了空字符串了呢?谁吃了我的参数值?
经过两个小时艰苦卓绝的调查取证(其中包含了到处搜索Asp.net MVC preview 2源码,以及试图使用Reflector重建源项目未遂),最后灵机一动,把"id"改成"taskId",于是就一切正常了.
结论很显然,"id"这个参数名在默认情况下是受到特殊对待的,只能在URL里附带,不能post..