PartialViewResult不鸟_ViewStart.cshtml

概述

  在ASP.NET MVC中,对于Action中得到的ActionResult如果是一个ViewResult对象,那么在进行View呈现时,则会先执行_ViewStart.cshtml,然后再去执行被请求的视图页,但是如果在控制器的Action中得到的ActionResult是一个PartialViewResult对象,那么在进行View呈现时,则不会执行_ViewStart.cshtml。

举例验证

例如:控制器代码如下:

    public class HomeController : Controller
    {
        public ActionResult Index()
        {
            return View("Index");
        }

        public ActionResult PartView()
        {
            return PartialView("Index");
        }
    }

⑴ 如果视图中设置如下,即:将 Layout = "~/Views/Shared/_Layout.cshtml";定义在Index.cshtml中。

则ViewResult和PartialViewResult的输出结果相同:

⑵ 如果视图设置如下,即:将 Layout = "~/Views/Shared/_Layout.cshtml";定义在_ViewStart.cshtml中。

则ViewResult和PartialViewResult的输出结果不同:

   以上的实例,我们可见断定,对于PartialViewResult对象进行View呈现时,不会执行 “_ViewStart.cshtml”(因为第二种情况下没有执行母板页中的代码),为了更加具有说服力,我们再来看看ASP.NET MVC源代码,并对比ViewResult和PartialViewResult来检查我们的猜想是否正确!!

源码验证

   由于对于ASP.NET MVC来说,进行View呈现的入口是执行ActionResult的ExecuteResult方法,而ViewResult和PartialViewResult都是继承自ViewResultBase类,在ViewResultBase中定义了ExecuteResult 方法!

public abstract class ViewResultBase : ActionResult
{
	//省略其他代码...
	
	public override void ExecuteResult(ControllerContext context)
	{
		if (context == null)
		{
			throw new ArgumentNullException("context");
		}
		if (string.IsNullOrEmpty(this.ViewName))
		{
			this.ViewName = context.RouteData.GetRequiredString("action");
		}
		ViewEngineResult viewEngineResult = null;
		if (this.View == null)
		{
			//执行FindView方法(在派生类中实现),通过视图引擎来创建视图对象!
			viewEngineResult = this.FindView(context);
			this.View = viewEngineResult.View;
		}
		TextWriter output = context.HttpContext.Response.Output;
		ViewContext viewContext = new ViewContext(context, this.View, this.ViewData, this.TempData, output);
		this.View.Render(viewContext, output);
		if (viewEngineResult != null)
		{
			viewEngineResult.ViewEngine.ReleaseView(context, this.View);
		}
	}
	//该方法在派生类ViewResult和PartialViewResult中实现
	protected abstract ViewEngineResult FindView(ControllerContext context);
}

   上图可以看出,在ViewResult和PartialViewResult的FindView方法中,分别通过base.ViewEngineCollection的FindView和FindPartialView来创建ViewEngineResult对象(用于封装当前请求的视图对象和视图引擎对象),我们知道base.ViewEngineCollection其实就是一个视图引擎集合(默认情况下有:RazorViewEngine、WebFormViewEngine),而视图引擎集合的FindView和FindPartialView方法,本质上就是遍历执行每个视图引擎的FindView和FindPartialView方法。

  由于我们使用的是Razor引擎,所有就以RazorViewEngine为例来介绍:

 

this.CreatePartialView(...)和this.CreateView(...)方法都实现在派生类中!

 

  上图中,我们可以看出在创建RazorView对象时,ViewResult和PartialViewResult的区别在于参数:runViewStartPages,正式由于它,决定了在之后执行进行视图页处理时,也就是执行RazorView对象的Render(viewContext, output)方法时,是否执行“_ViewStar.cshtml”。

public abstract class BuildManagerCompiledView : IView
{
	//省略其他代码...
	
	public void Render(ViewContext viewContext, TextWriter writer)
	{
		if (viewContext == null)
		{
			throw new ArgumentNullException("viewContext");
		}
		object obj = null;
		Type compiledType = this.BuildManager.GetCompiledType(this.ViewPath);
		if (compiledType != null)
		{
			obj = this._viewPageActivator.Create(this._controllerContext, compiledType);
		}
		if (obj == null)
		{
			throw new InvalidOperationException(string.Format(CultureInfo.CurrentCulture, MvcResources.CshtmlView_ViewCouldNotBeCreated, new object[]
			{
				this.ViewPath
			}));
		}
		this.RenderView(viewContext, writer, obj);
	}
	//实现在派生类中
	protected abstract void RenderView(ViewContext viewContext, TextWriter writer, object instance);
}

public class RazorView : BuildManagerCompiledView
{
	//省略其他代码...
	
	protected override void RenderView(ViewContext viewContext, TextWriter writer, object instance)
	{
		if (writer == null)
		{
			throw new ArgumentNullException("writer");
		}
		WebViewPage webViewPage = instance as WebViewPage;
		if (webViewPage == null)
		{
			throw new InvalidOperationException(string.Format(CultureInfo.CurrentCulture, MvcResources.CshtmlView_WrongViewBase, new object[]
			{
				base.ViewPath
			}));
		}
		webViewPage.OverridenLayoutPath = this.LayoutPath;
		webViewPage.VirtualPath = base.ViewPath;
		webViewPage.ViewContext = viewContext;
		webViewPage.ViewData = viewContext.ViewData;
		webViewPage.InitHelpers();
		if (this.VirtualPathFactory != null)
		{
			webViewPage.VirtualPathFactory = this.VirtualPathFactory;
		}
		if (this.DisplayModeProvider != null)
		{
			webViewPage.DisplayModeProvider = this.DisplayModeProvider;
		}
		WebPageRenderingBase startPage = null;
		//在这里这里这里这里....
		if (this.RunViewStartPages)
		{       //执行“_ViewStart.cshtml”中内容!
			startPage = this.StartPageLookup(webViewPage, RazorViewEngine.ViewStartFileName, this.ViewStartFileExtensions);
		}
		WebPageBase arg_D3_0 = webViewPage;
		HttpContextBase httpContext = viewContext.HttpContext;
		WebPageRenderingBase page = null;
		object model = null;
		arg_D3_0.ExecutePageHierarchy(new WebPageContext(httpContext, page, model), writer, startPage);
	}
}

  

 

posted @ 2014-01-12 00:20  武沛齐  阅读(2647)  评论(1编辑  收藏  举报