MVC ViewEngine视图引擎解读及autofac的IOC运用实践

Posted 2020-07-05

MVC 三大特色  Model、View、Control ，这次咱们讲视图引擎ViewEngine

1.首先看看IViewEngine接口的定义

namespace System.Web.Mvc
{
    public interface IViewEngine
    {
        ViewEngineResult FindPartialView(ControllerContext controllerContext, string partialViewName, bool useCache);
        ViewEngineResult FindView(ControllerContext controllerContext, string viewName, string masterName, bool useCache);
        void ReleaseView(ControllerContext controllerContext, IView view);
    }
}

2.默认情况下，ASP.NET MVC提供2种视图引擎：WebFormViewEngine，RazorViewEngine

namespace System.Web.Mvc
{
    public static class ViewEngines
    {
        private static readonly ViewEngineCollection _engines = new ViewEngineCollection
        {
            new WebFormViewEngine(),
            new RazorViewEngine(),
        };

        public static ViewEngineCollection Engines
        {
            get { return _engines; }
        }
    }
}

这就是为什么ASP.NET MVC既支持*.aspx，又支持*.cshtml的原因了。

那为什么所有的视图都要放在Views目录下呢，这个就要拜RazorViewngines所赐了。

namespace System.Web.Mvc
{
    public class RazorViewEngine : BuildManagerViewEngine
    {
        internal static readonly string ViewStartFileName = "_ViewStart";

        public RazorViewEngine()
            : this(null)
        {
        }

        public RazorViewEngine(IViewPageActivator viewPageActivator)
            : base(viewPageActivator)
        {
            AreaViewLocationFormats = new[]
            {
                "~/Areas/{2}/Views/{1}/{0}.cshtml",
                "~/Areas/{2}/Views/{1}/{0}.vbhtml",
                "~/Areas/{2}/Views/Shared/{0}.cshtml",
                "~/Areas/{2}/Views/Shared/{0}.vbhtml"
            };
            AreaMasterLocationFormats = new[]
            {
                "~/Areas/{2}/Views/{1}/{0}.cshtml",
                "~/Areas/{2}/Views/{1}/{0}.vbhtml",
                "~/Areas/{2}/Views/Shared/{0}.cshtml",
                "~/Areas/{2}/Views/Shared/{0}.vbhtml"
            };
            AreaPartialViewLocationFormats = new[]
            {
                "~/Areas/{2}/Views/{1}/{0}.cshtml",
                "~/Areas/{2}/Views/{1}/{0}.vbhtml",
                "~/Areas/{2}/Views/Shared/{0}.cshtml",
                "~/Areas/{2}/Views/Shared/{0}.vbhtml"
            };

            ViewLocationFormats = new[]
            {
                "~/Views/{1}/{0}.cshtml",
                "~/Views/{1}/{0}.vbhtml",
                "~/Views/Shared/{0}.cshtml",
                "~/Views/Shared/{0}.vbhtml"
            };
            MasterLocationFormats = new[]
            {
                "~/Views/{1}/{0}.cshtml",
                "~/Views/{1}/{0}.vbhtml",
                "~/Views/Shared/{0}.cshtml",
                "~/Views/Shared/{0}.vbhtml"
            };
            PartialViewLocationFormats = new[]
            {
                "~/Views/{1}/{0}.cshtml",
                "~/Views/{1}/{0}.vbhtml",
                "~/Views/Shared/{0}.cshtml",
                "~/Views/Shared/{0}.vbhtml"
            };

            FileExtensions = new[]
            {
                "cshtml",
                "vbhtml",
            };
        }

        protected override IView CreatePartialView(ControllerContext controllerContext, string partialPath)
        {
            return new RazorView(controllerContext, partialPath,
                                 layoutPath: null, runViewStartPages: false, viewStartFileExtensions: FileExtensions, 
                                 viewPageActivator: ViewPageActivator)
            {
                DisplayModeProvider = DisplayModeProvider
            };
        }

        protected override IView CreateView(ControllerContext controllerContext, string viewPath, string masterPath)
        {
            var view = new RazorView(controllerContext, viewPath,
                                     layoutPath: masterPath, runViewStartPages: true, viewStartFileExtensions: FileExtensions, viewPageActivator: V                                     iewPageActivator)
            {
                DisplayModeProvider = DisplayModeProvider
            };
            return view;
        }
    }
}

知道RazorViewEngine 内部定义，现在可以定制自己的需求啦

public sealed class CustomViewEngine : RazorViewEngine  
    {  
  
        public CustomViewEngine()  
        {  
            ViewLocationFormats = new[]  
            {  
                "~/Views/{1}/{0}.cshtml",  
                "~/Views/Shared/{0}.cshtml",  
                "~/CustomViewLocation/{1}/{0}.cshtml"  
            };  
        }  
        public override ViewEngineResult FindView(ControllerContext controllerContext, string viewName, string masterName, bool useCache)  
        {  
            return base.FindView(controllerContext, viewName, masterName, useCache);  
        }  
    }  

接下去就很简单了，只需要把原来的视图引擎清空，加载自己的视图引擎就可以了。

protected void Application_Start()  
{  
    AreaRegistration.RegisterAllAreas();  
  
    ViewEngines.Engines.Clear();  
  
    ViewEngines.Engines.Add(new CustomViewEngine());  
  
    RegisterGlobalFilters(GlobalFilters.Filters);  
    RegisterRoutes(RouteTable.Routes);  
}  

这样可以改变展示页面必须在View下的显示的局面，从而更加的灵活，为视图从Views拿出去 提供了必要条件，还需要一些其他操作：

 

      这个时候很明显,已经开始在我们自定义加的视图文件夹下面开始找视图了.但是找到了,却提示这个视图文件没派生自 WebViewPage 或 WebViewPage<TModel>。

我们知道Razor视图最终都会编译成一个类,这个类会自动继承WebViewPage 或 WebViewPage<TModel>,(这个是强类型视图了..)(大家可以用反编译工具看见)

但是我们把视图从Views下面拿出来了, MVC框架就不会编译的时候让他继承WebViewPage 或 WebViewPage<TModel>

     解决方案：

     第一种:这种最简单.把Views下面的web.config文件复制一个到MyCustomView下面,这样错误就没有了!就可以正常访问找到视图了

原理就是

上图中Views文件夹下面的Web.config中有一个节点配置了这么一句话<pages pageBaseType="System.Web.Mvc.WebViewPage"> .很明显是继承WebViewPage 的意思

有这个,此文件夹里面所有的视图编译的时候会自动运行这个,肯定就继承了WebViewPage

视图文件多的时候很适合这样做哦

我们知道ASP.NET框架对Web.config是 有就近原则和继承原则的,也就是你在网站根目录的Web.config下面的配置,适用于网站下面所有的程序,当你在子文件下面再有Web.config 的时候,他会就近选择使用(如果配置局部,想不使用全局配置,就可以自己加一个配置文件哦,是不是有点类似CSS中的就近原则,哈哈)

第二种:直接在视图中加一句指令

@inherits System.Web.Mvc.WebViewPage

作用不言而喻,当前视图会继承WebViewPage ,但多个视图的时候每个里面都写一句这个烦不烦!!所以不推挤这个啦!

参考链接：http://www.cnblogs.com/chengxiaohui/articles/4837193.html

              http://blog.csdn.net/jackvs/article/details/7788743