PartialViewResult不鸟_ViewStart.cshtml

浏览数：60 / 时间：2015年06月09日

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);
    }
}