异常处理是每一个系统都必须要有的功能,尤其对于Web系统而言,简单、统一的异常处理模式尤为重要,当打算使用ASP.NET MVC来做项目时,第一个数据录入页面就遇到了这个问题。

在之前的ASP.NET WebForm项目中,一般情况下都是在Application_Error事件处理器和ScriptManager_AsyncPostBackError事件处理器里面进行,在ASP.NET MVC中用这两种方法似乎都不合适了,该放在哪儿呢?总不至于在每个Action里面都放一个try{...}catch{...}吧。

在ScottGu的博客里面提到了一个类:HandleErrorAttribute,似乎是用于处理异常的,于是使用HandleErrorAttribute来做个尝试,(说明,如果使用了该类型,并且想把异常显示在自已指定的View,则必须在web.config里面的<system.web>节点加上<customErrors mode="On" />)发现HandleError的确比较好用,可以使用其View属性指定异常后跳转的页面,可以针对不同的异常类型跳到不同的异常显示View,而且也可以不跳转到异常显示View,显示到当前View,例:

        [HttpPost]
        [HandleError(View = "Create", ExceptionType = typeof(Exception))]
        public ActionResult Create(string someParam)
        {
            throw new Exception("oops...");
        }

当异常发生时,页面还会跳回到Create,只是这里有点小问题,用户在页面上输入了很多东西,你提示个异常不至于把他辛辛苦苦输了半天的东西都没有了吧,把这样的项目送出去,迟早是要改回来的。

打开HandleErrorAttribute的源代码可以看其关键部分:

        public virtual void OnException(ExceptionContext filterContext) {
            if (filterContext == null) {
                throw new ArgumentNullException("filterContext");
            }
            if (filterContext.IsChildAction) {
                return;
            }

            // If custom errors are disabled, we need to let the normal ASP.NET exception handler
            // execute so that the user can see useful debugging information.
            if (filterContext.ExceptionHandled || !filterContext.HttpContext.IsCustomErrorEnabled) {
                return;
            }

            Exception exception = filterContext.Exception;

            // If this is not an HTTP 500 (for example, if somebody throws an HTTP 404 from an action method),
            // ignore it.
            if (new HttpException(null, exception).GetHttpCode() != 500) {
                return;
            }

            if (!ExceptionType.IsInstanceOfType(exception)) {
                return;
            }

            string controllerName = (string)filterContext.RouteData.Values["controller"];
            string actionName = (string)filterContext.RouteData.Values["action"];
            HandleErrorInfo model = new HandleErrorInfo(filterContext.Exception, controllerName, actionName);
            filterContext.Result = new ViewResult {
                ViewName = View,
                MasterName = Master,
                ViewData = new ViewDataDictionary<HandleErrorInfo>(model),
                TempData = filterContext.Controller.TempData
            };
            filterContext.ExceptionHandled = true;
            filterContext.HttpContext.Response.Clear();
            filterContext.HttpContext.Response.StatusCode = 500;

            // Certain versions of IIS will sometimes use their own error page when
            // they detect a server error. Setting this property indicates that we
            // want it to try to render ASP.NET MVC's error page instead.
            filterContext.HttpContext.Response.TrySkipIisCustomErrors = true;
        }

可以很清楚的看到,MVC实际上是使用刚才我们指定的View名称新建了一个ViewResult,然后将这个ViewResult交给了InvokeActionResult方法,最终显示给了用户。在这个过程中,新的ViewResult的ViewData被设定为HandleErrorInfo了,没有将Create上的数据放进ViewData,尽管在之后显示的Create视图的Request里还保存着之前的Params内容,但是数据却没有加载上去,我也没有去深究,感觉如果在这里直接把filterContext.Controller中的ViewData直接作为新的ViewResult的ViewData的话,肯定是可以显示提交之前的数据的(因为如果将异常代码包在try...catch...里面是可以在异常后显示之前数据的)。

于是自已新建一个ExceptionFitler:

    public class CustomHandleErrorAttribute : FilterAttribute, IExceptionFilter
    {
        public void OnException(ExceptionContext filterContext)
        {
            filterContext.Controller.ViewData["Exception"] = filterContext.Exception;
            filterContext.Result = new ViewResult() { ViewName = filterContext.Controller.ControllerContext.RouteData.Values["Action"].ToString(), ViewData = filterContext.Controller.ViewData };
            filterContext.ExceptionHandled = true;
            filterContext.HttpContext.Response.TrySkipIisCustomErrors = true;
        }
    }

类名起的不咋的,将就着用吧:)

将原来的Action修改如下:

        [HttpPost]
        [CustomHandleError]
        public ActionResult Create(string Name)
        {
            throw new Exception("oops...");
        }

Create.csthml中加入如下代码:

    if (ViewData["Exception"] != null)
    {
        var ex = ViewData["Exception"] as Exception;
        @ex.Message
    }

F5,果然在提交后又回到了原来视图,而且之前填写的数据都还在。

3月19日完善如下:-----------------------------------------

namespace System.Web.Mvc
{
    public class HandleExceptionAttribute : HandleErrorAttribute, IExceptionFilter
    {
        #region IExceptionFilter Members

        public override void OnException(ExceptionContext filterContext)
        {
            if (filterContext == null)
            {
                throw new ArgumentNullException("filterContext");
            }
            if (filterContext.IsChildAction)
            {
                return;
            }

            // If custom errors are disabled, we need to let the normal ASP.NET exception handler
            // execute so that the user can see useful debugging information.
            if (filterContext.ExceptionHandled || !filterContext.HttpContext.IsCustomErrorEnabled)
            {
                return;
            }

            Exception exception = filterContext.Exception;

            // If this is not an HTTP 500 (for example, if somebody throws an HTTP 404 from an action method),
            // ignore it.
            if (new HttpException(null, exception).GetHttpCode() != 500)
            {
                return;
            }

            if (!ExceptionType.IsInstanceOfType(exception))
            {
                return;
            }

            string actionName = (string)filterContext.RouteData.Values["action"];
            filterContext.Controller.ViewData["Exception"] = exception;
            filterContext.Result = new ViewResult() { ViewName = actionName, ViewData = filterContext.Controller.ViewData };
            filterContext.ExceptionHandled = true;
            filterContext.HttpContext.Response.Clear();
            filterContext.HttpContext.Response.StatusCode = 500;
            filterContext.HttpContext.Response.TrySkipIisCustomErrors = true;
        }

        #endregion
    }

    public static class HandleExceptionHelper
    {
        public static Exception Exception(this HtmlHelper htmlhelper)
        {
            var exception = htmlhelper.ViewContext.Controller.ViewData["Exception"] as Exception;
            return exception;
        }
    }
}

View运用如下:

    if (@Html.Exception() != null)
    {
        @Html.Exception().Message
    }

3月20日添加生成jQuery错误样式:------------------------------------------------

    public static class HandleExceptionHelper
    {
        public static Exception Exception(this HtmlHelper htmlhelper)
        {
            var exception = htmlhelper.ViewContext.Controller.ViewData["Exception"] as Exception;
            return exception;
        }

        public static MvcHtmlString jQueryStyleError(this HtmlHelper htmlhelper)
        {
            var exception = Exception(htmlhelper);

            if (exception == null)
            {
                return null;
            }

            TagBuilder builder = new TagBuilder("div");
            builder.GenerateId("editordescription");
            builder.AddCssClass("ui-widget ui-state-error ui-corner-all");
            builder.InnerHtml = string.Format(@"<p><span class=""ui-icon ui-icon-alert"" style=""float: left; margin-right: .3em;""></span><strong>{0}: </strong>{1}</p>",
                Resx.Error, string.IsNullOrEmpty(exception.Message) ? Resx.UnknowErrorMessage : exception.Message);

            return new MvcHtmlString(builder.ToString(TagRenderMode.Normal));
        }
    }

View应用如下:

@Html.jQueryStyleError()

效果如下:

posted on 2011-03-18 11:10  think8848  阅读(6794)  评论(8编辑  收藏  举报