ASP.NET MVC - 定制属于你自己的ViewEngine

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

ASP.NET MVC出来这么久了，心中却又很多的疑惑：为什么所有的View都要放在Views目录下? 为什么Shared文件夹下面的页面可以被共享? 为什么Page既可以是*.cshtml，也可以是*.aspx?

其实上面的几个问题归结起来都是视图引擎的功效。

在传统的ASP.NET中，可能还没有ViewEngine的概念。因为在Web From里面，实现Page实现了IHttpHanlder的接口，所以Page既是响应的处理类，也是视图的渲染类。在ASP.NET MVC中，视图的概念被抽象了出来，试图引擎的概念也被抽象成了一个接口。

首先来看一下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);
    }
}

总共3个函数，总结起来大概就是两个功能：Find & Release。

默认情况下，ASP.NET MVC提供了两个视图引擎：WebFormViewEngine和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（个人觉得如果已经确定要使用RazorView的话，不如把WebFormViewEngine给移除，可能对性能会有所帮助）。

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。

下面是RazorViewEngine的构造函数：

        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",
            };
        }

所有的寻址路径都被格式化了，是不是很眼熟呢，关于这里为啥用数组而不用List，个人觉得，数组的寻址效率要更高些，遍历速度更快。

好了，找了“罪魁祸首”，就好好地调教一个，让它乖乖听话，小样让去哪就去哪里。

namespace MvcApplicatin.Web.Mvc.ViewEngine
{
    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);
        }
    }
}

我使用开发语言是C#，视图是Razor，所以稍稍修改了下ViewLocationFormats，让寻址路径能够寻到CustomViewLocation下面的视图。

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);
        }