使用ASP.NET MVC時，我們知道，要使用Views中的視圖，需要在Action中寫

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return View();

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這個方法返回的返回值是一個 ViewResult，進入這個類，繼承了父類ViewResultBase后只寫了MasterName屬性和FindView方法。

不過已經開始看到到ViewEngine的蹤影了。

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

跟進ViewEngineCollection.FindView去看看。

來到了ViewEngineCollection類，這是一個實現了Collection<IViewEngine>的類。

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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));} ? 很簡單的一個方法，跟進去 ? 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的有點不知所措，其實仔細一看結合上面的Find參數就能找到黃色加亮的幾句代碼關鍵代碼。

是遍歷了注冊ViewEngine集合，調用ViewEngine各自的FindView，誰能找到View，就用誰。

那么遍歷的ViewEngine集合怎么來的呢？要回到ViewResult的父類ViewResultBase中去看。

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

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如果沒有定義那么就調用ViewEngines.Engines，這是一個很簡單的靜態類屬性

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

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回到剛才的遍歷，由于RazorViewEngine的構造函數中定義了以下格式，在Views文件夾中也創建了相應的文件，所以選擇了RazorViewEngine。

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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，終于找到了Razor。

轉載于:https://www.cnblogs.com/llcto/archive/2012/06/02/2531470.html

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