asp.net-mvc - 通用继承的ViewPage <>和新属性

设定:

CustomViewEngine

CustomController基础

CustomViewPage Base(在此基础上，添加了一个新属性“MyCustomProperty”)

问题:

当 View 被强类型化时，例如:<@ Page Inherits="CustomViewPage<MyCustomObject" MyCustomProperty="Hello">，我得到一个编译器“Parser”错误，指出MyCustomProperty不是System.Web.Mvc.ViewPage的公共(public)属性。

我进行了无数次尝试和错误(请参见下文)，以了解导致此错误的原因，并得出以下结论:

仅当我在 View 的@Page指令中声明“MyCustomProperty”或任何其他属性时，才会发生错误。

该错误将始终显示“System.Web.Mvc.ViewPage”，而不是已声明的Inherits =“..”类。

最佳答案

更新:好像Technitium找到了另一种方法来做到这一点，至少在新版本的ASP.NET MVC上看起来更容易。 (在下面复制了他的评论)

<%@ Page Language="C#" MyNewProperty="From @Page directive!"
    Inherits="JG.ParserFilter.CustomViewPage<MvcApplication1.Models.FooModel>

<%@ Page Language="C#" MyNewProperty="From @Page directive!"`
    Inherits="JG.ParserFilter.CustomViewPage`1[MvcApplication1.Models.FooModel]>

下面的原始答案:

好，我解决了这是一次引人入胜的练习，一旦您第一次使用它，解决方案就很简单了，但并不太难。

这是潜在的问题:ASP.NET页面解析器不支持将泛型作为页面类型。

ASP.NET MVC解决此问题的方法是通过使基础页面解析器欺骗以为该页面不是通用的。他们通过构建自定义PageParserFilter和自定义FileLevelPageControlBuilder来实现此目的。解析器筛选器查找通用类型，如果找到通用类型，则将其替换为非通用ViewPage类型，以使ASP.NET解析器不会阻塞。然后，在页面编译生命周期的后半段，他们的自定义页面构建器类又将通用类型交换回去。

这是可行的，因为通用ViewPage类型是从非通用ViewPage派生的，并且@Page指令中设置的所有有趣属性都存在于(非通用)基类上。因此，在@Page指令中设置属性时，真正发生的事情是针对非通用ViewPage基类对这些属性名称进行了验证。

无论如何，这在大多数情况下都很好用，但在您的情况下却不行，因为他们将ViewPage硬编码为页面过滤器实现中的非通用基本类型，并且没有提供简单的更改方法。这就是为什么您在错误消息中始终看到ViewPage的原因，因为该错误发生在ASP.NET在ViewPage占位符中进行交换与在交换之前立即交换通用ViewPage之间的时间之间。

解决方法是创建您自己的以下版本:

页面解析器过滤器-这几乎是MVC源代码中ViewTypeParserFilter.cs的精确副本，唯一的区别是它引用的是自定义ViewPage和页面构建器类型，而不是MVC的

页面生成器-与MVC源代码中的ViewPageControlBuilder.cs相同，但是它将类放置在您自己的 namespace 中，而不是它们的 namespace 中。

直接从System.Web.Mvc.ViewPage(非通用版本)派生自定义 View 页类。将任何自定义属性粘贴到此新的非泛型类上。

从＃3派生一个通用类，从ASP.NET MVC源的ViewPage实现中复制代码。

如果您还需要用户控件指令上的自定义属性，则

对用户控件(@Control)重复＃2，＃3和＃4。

然后，您需要在 View 目录中更改web.config(而不是主应用程序的web.config)以使用这些新类型，而不是MVC的默认类型。

我随附了一些代码示例，说明了其工作原理。非常感谢Phil Haack的文章帮助我理解了这一点，尽管我也不得不花很多时间研究MVC和ASP.NET源代码才能真正理解它。

首先，我将从您的web.config中需要的web.config更改开始:

<pages
    validateRequest="false"
    pageParserFilterType="JG.ParserFilter.CustomViewTypeParserFilter"
    pageBaseType="JG.ParserFilter.CustomViewPage"
    userControlBaseType="JG.ParserFilter.CustomViewUserControl">

现在，这是页面解析器过滤器(上面的＃1):

namespace JG.ParserFilter {
    using System;
    using System.Collections;
    using System.Web.UI;
    using System.Web.Mvc;

    internal class CustomViewTypeParserFilter : PageParserFilter
    {

        private string _viewBaseType;
        private DirectiveType _directiveType = DirectiveType.Unknown;
        private bool _viewTypeControlAdded;

        public override void PreprocessDirective(string directiveName, IDictionary attributes) {
            base.PreprocessDirective(directiveName, attributes);

            string defaultBaseType = null;

            // If we recognize the directive, keep track of what it was. If we don't recognize
            // the directive then just stop.
            switch (directiveName) {
                case "page":
                    _directiveType = DirectiveType.Page;
                    defaultBaseType = typeof(JG.ParserFilter.CustomViewPage).FullName;  // JG: inject custom types here
                    break;
                case "control":
                    _directiveType = DirectiveType.UserControl;
                    defaultBaseType = typeof(JG.ParserFilter.CustomViewUserControl).FullName; // JG: inject custom types here
                    break;
                case "master":
                    _directiveType = DirectiveType.Master;
                    defaultBaseType = typeof(System.Web.Mvc.ViewMasterPage).FullName;
                    break;
            }

            if (_directiveType == DirectiveType.Unknown) {
                // If we're processing an unknown directive (e.g. a register directive), stop processing
                return;
            }


            // Look for an inherit attribute
            string inherits = (string)attributes["inherits"];
            if (!String.IsNullOrEmpty(inherits)) {
                // If it doesn't look like a generic type, don't do anything special,
                // and let the parser do its normal processing
                if (IsGenericTypeString(inherits)) {
                    // Remove the inherits attribute so the parser doesn't blow up
                    attributes["inherits"] = defaultBaseType;

                    // Remember the full type string so we can later give it to the ControlBuilder
                    _viewBaseType = inherits;
                }
            }
        }

        private static bool IsGenericTypeString(string typeName) {
            // Detect C# and VB generic syntax
            // REVIEW: what about other languages?
            return typeName.IndexOfAny(new char[] { '<', '(' }) >= 0;
        }

        public override void ParseComplete(ControlBuilder rootBuilder) {
            base.ParseComplete(rootBuilder);

            // If it's our page ControlBuilder, give it the base type string
            CustomViewPageControlBuilder pageBuilder = rootBuilder as JG.ParserFilter.CustomViewPageControlBuilder; // JG: inject custom types here
            if (pageBuilder != null) {
                pageBuilder.PageBaseType = _viewBaseType;
            }
            CustomViewUserControlControlBuilder userControlBuilder = rootBuilder as JG.ParserFilter.CustomViewUserControlControlBuilder; // JG: inject custom types here
            if (userControlBuilder != null) {
                userControlBuilder.UserControlBaseType = _viewBaseType;
            }
        }

        public override bool ProcessCodeConstruct(CodeConstructType codeType, string code) {
            if (codeType == CodeConstructType.ExpressionSnippet &&
                !_viewTypeControlAdded &&
                _viewBaseType != null &&
                _directiveType == DirectiveType.Master) {

                // If we're dealing with a master page that needs to have its base type set, do it here.
                // It's done by adding the ViewType control, which has a builder that sets the base type.

                // The code currently assumes that the file in question contains a code snippet, since
                // that's the item we key off of in order to know when to add the ViewType control.

                Hashtable attribs = new Hashtable();
                attribs["typename"] = _viewBaseType;
                AddControl(typeof(System.Web.Mvc.ViewType), attribs);
                _viewTypeControlAdded = true;
            }

            return base.ProcessCodeConstruct(codeType, code);
        }

        // Everything else in this class is unrelated to our 'inherits' handling.
        // Since PageParserFilter blocks everything by default, we need to unblock it

        public override bool AllowCode {
            get {
                return true;
            }
        }

        public override bool AllowBaseType(Type baseType) {
            return true;
        }

        public override bool AllowControl(Type controlType, ControlBuilder builder) {
            return true;
        }

        public override bool AllowVirtualReference(string referenceVirtualPath, VirtualReferenceType referenceType) {
            return true;
        }

        public override bool AllowServerSideInclude(string includeVirtualPath) {
            return true;
        }

        public override int NumberOfControlsAllowed {
            get {
                return -1;
            }
        }

        public override int NumberOfDirectDependenciesAllowed {
            get {
                return -1;
            }
        }

        public override int TotalNumberOfDependenciesAllowed {
            get {
                return -1;
            }
        }

        private enum DirectiveType {
            Unknown,
            Page,
            UserControl,
            Master,
        }
    }
}

这是页面构建器类(上面的＃2):

namespace JG.ParserFilter {
    using System.CodeDom;
    using System.Web.UI;

    internal sealed class CustomViewPageControlBuilder : FileLevelPageControlBuilder {
        public string PageBaseType {
            get;
            set;
        }

        public override void ProcessGeneratedCode(
            CodeCompileUnit codeCompileUnit,
            CodeTypeDeclaration baseType,
            CodeTypeDeclaration derivedType,
            CodeMemberMethod buildMethod,
            CodeMemberMethod dataBindingMethod) {

            // If we find got a base class string, use it
            if (PageBaseType != null) {
                derivedType.BaseTypes[0] = new CodeTypeReference(PageBaseType);
            }
        }
    }
}

这是自定义 View 页面类:非通用基类(上面的＃3)和通用派生类(上面的＃4):

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Diagnostics.CodeAnalysis;
using System.Web.Mvc;

namespace JG.ParserFilter
{
    [FileLevelControlBuilder(typeof(JG.ParserFilter.CustomViewPageControlBuilder))]
    public class CustomViewPage : System.Web.Mvc.ViewPage //, IAttributeAccessor
    {
        public string MyNewProperty { get; set; }
    }

    [FileLevelControlBuilder(typeof(JG.ParserFilter.CustomViewPageControlBuilder))]
    public class CustomViewPage<TModel> : CustomViewPage
        where TModel : class
    {
        // code copied from source of ViewPage<T>

        private ViewDataDictionary<TModel> _viewData;

        public new AjaxHelper<TModel> Ajax
        {
            get;
            set;
        }

        public new HtmlHelper<TModel> Html
        {
            get;
            set;
        }

        public new TModel Model
        {
            get
            {
                return ViewData.Model;
            }
        }

        [SuppressMessage("Microsoft.Usage", "CA2227:CollectionPropertiesShouldBeReadOnly")]
        public new ViewDataDictionary<TModel> ViewData
        {
            get
            {
                if (_viewData == null)
                {
                    SetViewData(new ViewDataDictionary<TModel>());
                }
                return _viewData;
            }
            set
            {
                SetViewData(value);
            }
        }

        public override void InitHelpers()
        {
            base.InitHelpers();

            Ajax = new AjaxHelper<TModel>(ViewContext, this);
            Html = new HtmlHelper<TModel>(ViewContext, this);
        }

        protected override void SetViewData(ViewDataDictionary viewData)
        {
            _viewData = new ViewDataDictionary<TModel>(viewData);

            base.SetViewData(_viewData);
        }

    }
}

这是用户控件的相应类(上面的＃5):

namespace JG.ParserFilter
{
    using System.Diagnostics.CodeAnalysis;
    using System.Web.Mvc;
    using System.Web.UI;

    [FileLevelControlBuilder(typeof(JG.ParserFilter.CustomViewUserControlControlBuilder))]
    public class CustomViewUserControl : System.Web.Mvc.ViewUserControl
    {
        public string MyNewProperty { get; set; }
    }

    public class CustomViewUserControl<TModel> : CustomViewUserControl  where TModel : class
    {
        private AjaxHelper<TModel> _ajaxHelper;
        private HtmlHelper<TModel> _htmlHelper;
        private ViewDataDictionary<TModel> _viewData;

        public new AjaxHelper<TModel> Ajax {
            get {
                if (_ajaxHelper == null) {
                    _ajaxHelper = new AjaxHelper<TModel>(ViewContext, this);
                }
                return _ajaxHelper;
            }
        }

        public new HtmlHelper<TModel> Html {
            get {
                if (_htmlHelper == null) {
                    _htmlHelper = new HtmlHelper<TModel>(ViewContext, this);
                }
                return _htmlHelper;
            }
        }

        public new TModel Model {
            get {
                return ViewData.Model;
            }
        }

        [SuppressMessage("Microsoft.Usage", "CA2227:CollectionPropertiesShouldBeReadOnly")]
        public new ViewDataDictionary<TModel> ViewData {
            get {
                EnsureViewData();
                return _viewData;
            }
            set {
                SetViewData(value);
            }
        }

        protected override void SetViewData(ViewDataDictionary viewData) {
            _viewData = new ViewDataDictionary<TModel>(viewData);

            base.SetViewData(_viewData);
        }
    }
}

namespace JG.ParserFilter {
    using System.CodeDom;
    using System.Web.UI;

    internal sealed class CustomViewUserControlControlBuilder : FileLevelUserControlBuilder {
        internal string UserControlBaseType {
            get;
            set;
        }

        public override void ProcessGeneratedCode(
            CodeCompileUnit codeCompileUnit,
            CodeTypeDeclaration baseType,
            CodeTypeDeclaration derivedType,
            CodeMemberMethod buildMethod,
            CodeMemberMethod dataBindingMethod) {

            // If we find got a base class string, use it
            if (UserControlBaseType != null) {
                derivedType.BaseTypes[0] = new CodeTypeReference(UserControlBaseType);
            }
        }
    }
}

最后，这是一个示例 View ，它显示了运行情况:

<%@ Page Language="C#" MyNewProperty="From @Page directive!"  Inherits="JG.ParserFilter.CustomViewPage<MvcApplication1.Models.FooModel>" %>
    <%=Model.SomeString %>
    <br /><br />this.MyNewPrroperty = <%=MyNewProperty%>
</asp:Content>