ASP.NET MVC 在控制器中擷取某個視圖動態HTML代碼

如果我們需要動態用AJAX從伺服器端擷取HTML代碼，拼接字串是一種不好的方式，所以我們將HTML代碼寫在cshtml檔案中，然後通過代碼傳入model，動態擷取cshtml中的HTML代碼

當然，我們想要使用通用的方法去擷取cshtml，就必須重寫RazorViewEngine視圖引擎，配置視圖搜尋位置

在尋找一個視圖時，Razor視圖引擎遵循了MVC架構早期版本建立起來的約定。例如，如果你請求與Home控制器相關的Index視圖，Razor會審查這樣的視圖列表：

 ~/Views/Home/Index.cshtml
● ~/Views/Home/Index.vbhtml
● ~/Views/Shared/Index.cshtml
● ~/Views/Shared/Index.vbhtml

正如你現在知道的，Razor實際上不會在磁碟上尋找這些視圖檔案，因為它們還沒有被編譯成C#類。Razor尋找的是表示這些視圖的編譯類。.cshtml檔案是含有C#語句的模板（我們正在使用的這種），而.vbhtml檔案含有Visual Basic語句。

你可以通過產生一個RazorViewEngine子類，來改變Razor搜尋的這種視圖檔案。這個類是Razor的IViewEngine實現。它建立於一組基類之上，這些類定義一組用來確定搜尋哪種視圖檔案的屬性。這些屬性如表所描述。

Property 屬性	Description 描述	Default Value 預設值
ViewLocationFormats MasterLocationFormats PartialViewLocationFormats	The locations to look for views, partial views, and layouts 查詢檢視表、分部視圖、以及布局的位置	"~/Views/{1}/{0}.cshtml", "~/Views/{1}/{0}.vbhtml", "~/Views/Shared/{0}.cshtml", "~/Views/Shared/{0}.vbhtml"
AreaViewLocationFormats AreaMasterLocationFormats AreaPartialViewLocationFormats	The locations to look for views, partial views, and layouts for an area 尋找一個地區的視圖、分部視圖、及布局的位置	"~/Areas/{2}/Views/{1}/{0}.cshtml", "~/Areas/{2}/Views/{1}/{0}.vbhtml", "~/Areas/{2}/Views/Shared/{0}.cshtml", "~/Areas/{2}/Views/Shared/{0}.vbhtml"

 這些屬性先於Razor的引入，這是每組三個屬性具有相同值的原因。每個屬性是一個字串數組，它們是用複合字元串格式化符號來表示的。以下是與預留位置對應的參數值：
● {0} represents the name of the view.
{0} 表示視圖名
● {1} represents the name of the controller.
{1} 表示控制器名
● {2} represents the name of the area.
{2} 表示地區名
為了修改搜尋位置，你要產生一個派生於RazorViewEngine的新類，並修改表所描述的一個或多個屬性值。

在Infrastructure檔案夾中建立一個CustomRazorViewEngine類

using System;using System.Collections.Generic;using System.Linq;using System.Web;using System.Web.Mvc;namespace MvcApplication1.Infrastructure{    public class CustomRazorViewEngine : RazorViewEngine    {        public CustomRazorViewEngine()        {            ViewLocationFormats = new string[] {                "~/Views/{1}/{0}.cshtml",                 "~/Views/Shared/{0}.cshtml",                  "~/Views/Shared_PartialView/{0}.cshtml"//指定尋找某個檔案的路徑            };            PartialViewLocationFormats = new string[] {                "~/Views/{1}/{0}.cshtml",                 "~/Views/Shared/{0}.cshtml",                  "~/Views/Shared_PartialView/{0}.cshtml"////指定尋找某個檔案的路徑            };        }    }}

我們在Global.asax的Application_Start方法中，用ViewEngines.Engines集合來註冊我們的這個派生視圖引擎，像這樣：

protected void Application_Start()        {            AreaRegistration.RegisterAllAreas();            ViewEngines.Engines.Clear();            ViewEngines.Engines.Add(new CustomRazorViewEngine());            WebApiConfig.Register(GlobalConfiguration.Configuration);            FilterConfig.RegisterGlobalFilters(GlobalFilters.Filters);            RouteConfig.RegisterRoutes(RouteTable.Routes);            BundleConfig.RegisterBundles(BundleTable.Bundles);        }

擷取html字串的方法以及如何調用

public class HomeController : Controller    {        //        // GET: /Home/             public ActionResult Index()        {            string html =  this.ControllerContext.RenderViewToString("_CommonPartial", new UserViewModel() {  UserName="haha"});            return View(new UserViewModel() { IsEnable = false, UserCode = "aa" });        }          }    public static class HelperExtensions    {        public static string RenderViewToString(this ControllerContext context, string viewName, object model)        {            if (string.IsNullOrEmpty(viewName))                viewName = context.RouteData.GetRequiredString("action");            context.Controller.ViewData.Model = model;            using (var sw = new StringWriter())            {                ViewEngineResult viewResult = ViewEngines.Engines.FindPartialView(context, viewName);                var viewContext = new ViewContext(context,                                                  viewResult.View,                                                  context.Controller.ViewData,                                                  context.Controller.TempData,                                                  sw);                try                {                    viewResult.View.Render(viewContext, sw);                }                catch (Exception ex)                {                    throw;                }                return sw.GetStringBuilder().ToString();            }        }    }