当一个Action完成它的任务后，通常需要返回一个实现IActionResult的对象，而最常见的就是View或者ViewResult，所谓的视图对象。那么视图与最终所看到的页面之间的联系又是怎样形成的，这便是本文想要探讨的问题。
在ResourceInvoker类之中，可以找到下列的代码。这些代码是对返回结果——IActionResult的进一步处理。
case State.ResultInside: ???{ ???????... ???????var task = InvokeResultAsync(_result); ???????if (task.Status != TaskStatus.RanToCompletion) ???????{ ???????????next = State.ResultEnd; ???????????return task; ???????} ???????goto case State.ResultEnd; ???}protected async Task InvokeResultAsync(IActionResult result){ ???var actionContext = _actionContext; ???_diagnosticSource.BeforeActionResult(actionContext, result); ???_logger.BeforeExecutingActionResult(result); ???try ???{ ???????await result.ExecuteResultAsync(actionContext); ???} ???finally ???{ ???????_diagnosticSource.AfterActionResult(actionContext, result); ???????_logger.AfterExecutingActionResult(result); ???}}IActionResult接口的实现类ViewResult中会调用ViewResultExecutor类的方法。
public override async Task ExecuteResultAsync(ActionContext context){ ???... ???var executor = context.HttpContext.RequestServices.GetRequiredService<IActionResultExecutor<ViewResult>>(); ???await executor.ExecuteAsync(context, this);}ViewResultExecutor类里则需要先通过RazorViewEngine类找到对应的视图。
public async Task ExecuteAsync(ActionContext context, ViewResult result){ ???... ???var viewEngineResult = FindView(context, result); ???viewEngineResult.EnsureSuccessful(originalLocations: null); ???var view = viewEngineResult.View; ???using (view as IDisposable) ???{ ???????await ExecuteAsync( ???????????context, ???????????view, ???????????result.ViewData, ???????????result.TempData, ???????????result.ContentType, ???????????result.StatusCode); ???} ???...}RazorViewEngine类返回的结果是RazorView对象。注意其内部已包含了IRazorPage对象。
public ViewEngineResult GetView(string executingFilePath, string viewPath, bool isMainPage){ ???... ???var cacheResult = LocatePageFromPath(executingFilePath, viewPath, isMainPage); ???return CreateViewEngineResult(cacheResult, viewPath);}public ViewEngineResult FindView(ActionContext context, string viewName, bool isMainPage){ ???... ???var cacheResult = LocatePageFromViewLocations(context, viewName, isMainPage); ???return CreateViewEngineResult(cacheResult, viewName);}private ViewEngineResult CreateViewEngineResult(ViewLocationCacheResult result, string viewName){ ???... ???var page = result.ViewEntry.PageFactory(); ???var viewStarts = new IRazorPage[result.ViewStartEntries.Count]; ???for (var i = 0; i < viewStarts.Length; i++) ???{ ???????var viewStartItem = result.ViewStartEntries[i]; ???????viewStarts[i] = viewStartItem.PageFactory(); ???} ???var view = new RazorView(this, _pageActivator, viewStarts, page, _htmlEncoder, _diagnosticSource); ???return ViewEngineResult.Found(viewName, view);}找到视图后，ViewResultExecutor再调用其父类ViewExecutor的ExecuteAsync方法。其内部将调用RazorView类的RenderAsync方法。
protected async Task ExecuteAsync( ???ViewContext viewContext, ???string contentType, ???int? statusCode){ ???... ???var response = viewContext.HttpContext.Response; ???ResponseContentTypeHelper.ResolveContentTypeAndEncoding( ???????contentType, ???????response.ContentType, ???????DefaultContentType, ???????out var resolvedContentType, ???????out var resolvedContentTypeEncoding); ???response.ContentType = resolvedContentType; ???if (statusCode != null) ???{ ???????response.StatusCode = statusCode.Value; ???} ???using (var writer = WriterFactory.CreateWriter(response.Body, resolvedContentTypeEncoding)) ???{ ???????var view = viewContext.View; ???????var oldWriter = viewContext.Writer; ???????try ???????{ ???????????viewContext.Writer = writer; ???????????DiagnosticSource.BeforeView(view, viewContext); ???????????await view.RenderAsync(viewContext); ???????????DiagnosticSource.AfterView(view, viewContext); ???????} ???????finally ???????{ ???????????viewContext.Writer = oldWriter; ???????} ???????// Perf: Invoke FlushAsync to ensure any buffered content is asynchronously written to the underlying ???????// response asynchronously. In the absence of this line, the buffer gets synchronously written to the ???????// response as part of the Dispose which has a perf impact. ???????await writer.FlushAsync(); ???}}RazorView类中可以看到其核心的处理与IRazorPage的ExecuteAsync方法紧密相关。
public virtual async Task RenderAsync(ViewContext context){ ???... ???_bufferScope = context.HttpContext.RequestServices.GetRequiredService<IViewBufferScope>(); ???var bodyWriter = await RenderPageAsync(RazorPage, context, invokeViewStarts: true); ???await RenderLayoutAsync(context, bodyWriter);}private async Task<ViewBufferTextWriter> RenderPageAsync( ???IRazorPage page, ???ViewContext context, ???bool invokeViewStarts){ ???var writer = context.Writer as ViewBufferTextWriter; ???... ???// The writer for the body is passed through the ViewContext, allowing things like HtmlHelpers ???// and ViewComponents to reference it. ???var oldWriter = context.Writer; ???var oldFilePath = context.ExecutingFilePath; ???context.Writer = writer; ???context.ExecutingFilePath = page.Path; ???try ???{ ???????if (invokeViewStarts) ???????{ ???????????// Execute view starts using the same context + writer as the page to render. ???????????await RenderViewStartsAsync(context); ???????} ???????await RenderPageCoreAsync(page, context); ???????return writer; ???} ???finally ???{ ???????context.Writer = oldWriter; ???????context.ExecutingFilePath = oldFilePath; ???}}private async Task RenderPageCoreAsync(IRazorPage page, ViewContext context){ ???page.ViewContext = context; ???_pageActivator.Activate(page, context); ???_diagnosticSource.BeforeViewPage(page, context); ???try ???{ ???????await page.ExecuteAsync(); ???} ???finally ???{ ???????_diagnosticSource.AfterViewPage(page, context); ???}}但当查找IRazorPage接口的实现。从RazorPageBase到RazorPage，再到RazorPage<TModel>，这些都只是抽象类，且都没有对ExecuteAsync方法有具体实现。
源码里找不到进一步的实现类，线索到这里断开了。
这时可以建立一个MVC的应用程序，编译后找到它的bin目录，会看到其中包含一个*.View.dll文件。
使用反编译软件，比如dotPeek，查看里面的内容，会找到一些由cshtml文件生成的类。
以其中Views_Home_Index为例，其实际上为RazorPage<TModel>的一个实现类。
它内部的ExecuteAsync方法正是生成页面内容的关键。
因为是VS模板自动生成的页面，上面的代码十分冗杂。为了更清晰地检查核心的代码，不妨减少下页面的复杂度。
把index.cshtml文件内容改成如下：
@{ ???ViewData["Title"] = "Home Page"; ???Layout = null;}<p>Hello World!</p>再次编译后，可以看到ExecuteAsync方法的内容变成了下面的样子：
public virtual async Task ExecuteAsync(){ ?((ViewDataDictionary) this.get_ViewData()).set_Item("Title", (object) "Home Page"); ?((RazorPageBase) this).set_Layout((string) null); ?((RazorPageBase) this).BeginContext(65, 21, true); ?((RazorPageBase) this).WriteLiteral("\r\n<p>Hello World!</p>"); ?((RazorPageBase) this).EndContext();}不难看出，最终展现的页面内容便是通过RazorPageBase类的WriteLiteral方法生成的。
.NET Core开发日志——视图与页面
原文地址：https://www.cnblogs.com/kenwoo/p/9533725.html