使用ASP.NET MVC时，我们知道，要使用Views中的视图，需要在Action中写

return View();

这个方法返回的返回值是一个 ViewResult，进入这个类，继承了父类ViewResultBase后只写了MasterName属性和FindView方法。

不过已经开始看到到ViewEngine的踪影了。

        protected override ViewEngineResult FindView(ControllerContext context) {ViewEngineResult result = }

跟进ViewEngineCollection.FindView去看看。

来到了ViewEngineCollection类，这是一个实现了Collection<IViewEngine>的类。

        public virtual ViewEngineResult FindView(ControllerContext controllerContext, string viewName, string masterName) {if (controllerContext == null) {throw new ArgumentNullException("controllerContext");}if (string.IsNullOrEmpty(viewName)) {throw new ArgumentException(MvcResources.Common_NullOrEmpty, "viewName");}return Find(e => e.FindView(controllerContext, viewName, masterName, true),e => e.FindView(controllerContext, viewName, masterName, false));}

很简单的一个方法，跟进去

      private ViewEngineResult Find(Func<IViewEngine, ViewEngineResult> cacheLocator, Func<IViewEngine, ViewEngineResult> locator) {// First, look up using the cacheLocator and do not track the searched paths in non-matching view engines// Then, look up using the normal locator and track the searched paths so that an error view engine can be returnedreturn Find(cacheLocator, trackSearchedPaths: false)?? Find(locator, trackSearchedPaths: true);}private ViewEngineResult Find(Func<IViewEngine, ViewEngineResult> lookup, bool trackSearchedPaths) {// Returns//    1st result// OR list of searched paths (if trackSearchedPaths == true)// OR nullViewEngineResult result;List<string> searched = null;if (trackSearchedPaths) {searched = new List<string>();}foreach (IViewEngine engine in CombinedItems) {if (engine != null) {if (trackSearchedPaths) {searched.AddRange(result.SearchedLocations);}}}if (trackSearchedPaths) {// Remove duplicate search paths since multiple view engines could have potentially looked at the same pathreturn new ViewEngineResult(searched.Distinct().ToList());}else {return null;}}

乍一看，又是for又是if、else的有点不知所措，其实仔细一看结合上面的Find参数就能找到黄色加亮的几句代码关键代码。

是遍历了注册ViewEngine集合，调用ViewEngine各自的FindView，谁能找到View，就用谁。

那么遍历的ViewEngine集合怎么来的呢？要回到ViewResult的父类ViewResultBase中去看。

        public ViewEngineCollection ViewEngineCollection {get {return _viewEngineCollection ?? ViewEngines.Engines;}set {_viewEngineCollection = value;}}

如果没有定义那么就调用ViewEngines.Engines，这是一个很简单的静态类属性

    public static class ViewEngines {private readonly static ViewEngineCollection _engines = new ViewEngineCollection {new WebFormViewEngine(),new RazorViewEngine(),};public static ViewEngineCollection Engines {get {return _engines;}}}

回到刚才的遍历，由于RazorViewEngine的构造函数中定义了以下格式，在Views文件夹中也创建了相应的文件，所以选择了RazorViewEngine。

 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"};

好了，终于找到了Razor。