Razor视图引擎学习

RazorView:

　　RazorView和WebFormView都是继承自：BuildManageCompiledView。RazorView和WebFormView都有其各自对应的一个引擎:RazorViewEngine和WebFormViewEngine，今天咱们不讲WebFormView，主讲RazorView，我们来看看RazorView类型。在Razor引擎下，通过这一类型来表示View。

public class RazorView : BuildManagerCompiledView
{
    // Methods
    public RazorView(ControllerContext controllerContext, string viewPath, string layoutPath, bool runViewStartPages, IEnumerable<string> viewStartFileExtensions);
    public RazorView(ControllerContext controllerContext, string viewPath, string layoutPath, bool runViewStartPages, IEnumerable<string> viewStartFileExtensions, IViewPageActivator viewPageActivator);
    protected override void RenderView(ViewContext viewContext, TextWriter writer, object instance);

    // Properties
    internal DisplayModeProvider DisplayModeProvider { get; set; }
    public string LayoutPath { get; private set; }
    public bool RunViewStartPages { get; private set; }
    internal StartPageLookupDelegate StartPageLookup { get; set; }
    public IEnumerable<string> ViewStartFileExtensions { get; private set; }
    internal IVirtualPathFactory VirtualPathFactory { get; set; }
}

RenderView方法重写了基类BuildManagerCompiledView的方法。 属性LayoutPath表示布局文件的虚拟路径，而RunViewStartPages则表示是否运行ViewSatrt视图

，ViewStartFileExtensions属性则表示的是ViewStart文件的后缀。例如：“cshtml”、"vbhtml"。我们再来看看其内部的一个很重要的方法：RenderView.

  protected override void RenderView(ViewContext viewContext, TextWriter writer, object instance)
    {
        if (writer == null)
        {
            throw new ArgumentNullException("writer");
        }
        WebViewPage page = instance as WebViewPage;
        if (page == null)
        {
            throw new InvalidOperationException(string.Format(CultureInfo.CurrentCulture, MvcResources.CshtmlView_WrongViewBase, new object[] { base.ViewPath }));
        }
        page.OverridenLayoutPath = this.LayoutPath;
        page.VirtualPath = base.ViewPath;
        page.ViewContext = viewContext;
        page.ViewData = viewContext.ViewData;
        page.InitHelpers();
        if (this.VirtualPathFactory != null)
        {
            page.VirtualPathFactory = this.VirtualPathFactory;
        }
        if (this.DisplayModeProvider != null)
        {
            page.DisplayModeProvider = this.DisplayModeProvider;
        }
        WebPageRenderingBase startPage = null;
        if (this.RunViewStartPages)
        {
            startPage = this.StartPageLookup(page, RazorViewEngine.ViewStartFileName, this.ViewStartFileExtensions);
        }
        HttpContextBase httpContext = viewContext.HttpContext;
        WebPageRenderingBase base4 = null;
        object model = null;
        page.ExecutePageHierarchy(new WebPageContext(httpContext, base4, model), writer, startPage);
    }

在此方法中，首先是将传过来的object对象转换为一个WebViewPage对象，接着设置WebViewPage对象的page的布局文件路径，视图文件路径，以及ViewContext和ViewData属性。接着执行初始化，对WebViewPage内部的一些属性进行设置，接着判断执行ViewStart页面的情况，得到表示开启页面的WebPageRenderingBase对象。最后执行page对象的ExecutePageHierarchy方法， 运行执行管道的页层次结构。

来瞧瞧其基类：BuilderManagerCompiledView

public abstract class BuildManagerCompiledView : IView
{
　　　  // Methods11     internal BuildManagerCompiledView(ControllerContext controllerContext, string viewPath, IViewPageActivator viewPageActivator, IDependencyResolver dependencyResolver);
    public void Render(ViewContext viewContext, TextWriter writer);
    protected abstract void RenderView(ViewContext viewContext, TextWriter writer, object instance);

    // Properties
    internal IBuildManager BuildManager { get; set; }
    public string ViewPath { get; protected set; }
}

BuilderManagerCompiledView提供了一个RenderView的抽象方法供子类重写，上面我们已经讲过RenderView方法，可以参考。其中有一个Render方法，我们来看看：

public void Render(ViewContext viewContext, TextWriter writer)
{
    if (viewContext == null)
    {
        throw new ArgumentNullException("viewContext");
    }
    object instance = null;
    Type compiledType = this.BuildManager.GetCompiledType(this.ViewPath);
    if (compiledType != null)
    {
        instance = this.ViewPageActivator.Create(this._controllerContext, compiledType);
    }
    if (instance == null)
    {
        throw new InvalidOperationException(string.Format(CultureInfo.CurrentCulture, MvcResources.CshtmlView_ViewCouldNotBeCreated, new object[] { this.ViewPath }));
    }
    this.RenderView(viewContext, writer, instance);
}

该方法中，首先是根据虚拟路径获得所在View的类型，然在根据类型和控制器上下文创建对象，这个方法最终还是调用了RenderView方法，将instance对象作为参数带入方法中.

可能你对BuildManagerCompiledView构造函数也感兴趣，特别是IViewPageActivator和IDependencyResolver。

internal BuildManagerCompiledView(ControllerContext controllerContext, string viewPath, IViewPageActivator viewPageActivator, IDependencyResolver dependencyResolver)
{
    this._controllerContext = controllerContext;
    this.ViewPath = viewPath;
    this.ViewPageActivator = viewPageActivator ?? new BuildManagerViewEngine.DefaultViewPageActivator(dependencyResolver);
}

看到构造函数结尾对当前ViewPageActivator属性进行赋值的时候，给了一个默认值。看到了吧，当为null的时候，赋了一个DefaultViewPageActivator对象，此时构造函数中传入的参数是dependencyResolver对象。

Razor视图引擎：

public class RazorViewEngine : BuildManagerViewEngine
{
    // Fields
    internal static readonly string ViewStartFileName;

    // Methods
    static RazorViewEngine();
    public RazorViewEngine();
    public RazorViewEngine(IViewPageActivator viewPageActivator);
    protected override IView CreatePartialView(ControllerContext controllerContext, string partialPath);
    protected override IView CreateView(ControllerContext controllerContext, string viewPath, string masterPath);
}

RazorViewEngine继承自BuildManagerViewEngine，内部通过控制器上下文，重写了基类的CreatePartialView创建分布视图方法和CreateView创建视图方法。构造函数设置了视图的搜寻顺序，如果没有提供，则按照这个顺序进行搜寻。