ASP.NET MVC 中如何调用 Error.cshtml？

Question

我在 StackOverflow 上阅读了十几个类似的问题，但我似乎无法理解这一点。关于 web.config 和 HandleErrorAttribute 中的自定义错误节点，Error.cshtml 是如何被调用的？最终，这个问题的答案可能是已经存在的关于 ASP.NET MVC 错误处理的几个问题之一的答案。但是，事实是，我不知道是哪一个。

Answer 1

在您的 Global.asax 中，您有以下方法：

public static void RegisterGlobalFilters(GlobalFilterCollection filters)
{
    filters.Add(new HandleErrorAttribute());
}

这会将 HandleErrorAttribute 注册为全局操作过滤器。这意味着此处理程序会自动应用于所有控制器操作。现在我们通过查看源码来看看这个属性是如何实现的：

[SuppressMessage("Microsoft.Performance", "CA1813:AvoidUnsealedAttributes", Justification = "This attribute is AllowMultiple = true and users might want to override behavior.")]
[AttributeUsage(AttributeTargets.Class | AttributeTargets.Method, Inherited = true, AllowMultiple = true)]
public class HandleErrorAttribute : FilterAttribute, IExceptionFilter {

    private const string _defaultView = "Error";

    private readonly object _typeId = new object();

    private Type _exceptionType = typeof(Exception);
    private string _master;
    private string _view;

    public Type ExceptionType {
        get {
            return _exceptionType;
        }
        set {
            if (value == null) {
                throw new ArgumentNullException("value");
            }
            if (!typeof(Exception).IsAssignableFrom(value)) {
                throw new ArgumentException(String.Format(CultureInfo.CurrentCulture,
                    MvcResources.ExceptionViewAttribute_NonExceptionType, value.FullName));
            }

            _exceptionType = value;
        }
    }

    public string Master {
        get {
            return _master ?? String.Empty;
        }
        set {
            _master = value;
        }
    }

    public override object TypeId {
        get {
            return _typeId;
        }
    }

    public string View {
        get {
            return (!String.IsNullOrEmpty(_view)) ? _view : _defaultView;
        }
        set {
            _view = value;
        }
    }

    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;
    }
}

源代码包含 cmets 并且不仅仅是自我解释。它首先检查的是您是否在 web.config 中启用了自定义错误（即<customErrors mode="On">）。如果你没有，它什么都不做=> YSOD。如果您启用了自定义错误，则它会呈现错误视图，并向其传递一个包含异常堆栈跟踪和其他有用信息的模型。