asp.net mvc(十一)自定义view engine

        当创建一个asp.net mvc 1.0的项目后,在web工程中都会出现Views文件夹,这里面就是我们存放View Page或者是partial view的地方。而且系统对于Controller的名称以及Views文件夹下面的子文件夹名称均有一定的约束。

        例如，有一个名称为GuestBookController的Controller,这时我们创建View Page时，就需要在Views下面创建一个GuestBook的子文件夹，不能随便命名。然后把View page或者是partial view放进来，或者把文件放在Shared文件夹中也行,如果把view page放在web工程根目录下面，系统会找不到对应的view。

        本文解决问题：针对上面的局限性，我们能不能打破呢？即可以实现如下功能：

        第一：view page可以放在views之外的文件夹中。

        第二：view page的名称和Controller的名称取消名称上的约束，例如：view page名称是ViewContentPage1.aspx,而对应的Controller名称是testController.cs。

        实现原理：asp.net mvc之所以能根据用户请求找到对应的view page，主要是路由。这其中有一个重要的类WebFormViewEngine,它负责发现我们创建的view page或者是partial view。为此我们可以重写一个新的ViewEngine来完成我的目的。

        1:先看下webformviewengine的构造函数：

public WebFormViewEngine()
{
    base.MasterLocationFormats = new string[] { "~/Views/{1}/{0}.master", "~/Views/Shared/{0}.master" };
    base.ViewLocationFormats = new string[] { "~/Views/{1}/{0}.aspx", "~/Views/{1}/{0}.ascx", "~/Views/Shared/{0}.aspx", "~/Views/Shared/{0}.ascx" };
    base.PartialViewLocationFormats = base.ViewLocationFormats;
}

        base.ViewLocationFormats 可以看出view page为什么只能写在views文件夹下的原因了。所以我们只需要在新的view engine的构造函数中修改下base.ViewLocationFormats 路径即可。这里我创建一个新的WebViewEngine,它需要继承WebFormViewEngine。可以这样改写：这样第一点就完成了。
   

public WebViewEngine()
        {
            base.MasterLocationFormats = new string[] { "~/Views/{1}/{0}.master", "~/Views/Shared/{0}.master" };
            base.ViewLocationFormats = new string[] { 
                 "~/com/{0}.aspx",
                "~/com/{0}.ascx",
                "~/Views/{1}/{0}.aspx",
                "~/Views/{1}/{0}.ascx", 
                 "~/Common/Views/{0}.aspx",
               "~/Common/Views/{0}.ascx",
                "~/Views/Shared/{0}.aspx",
                "~/Views/Shared/{0}.ascx" };
            base.PartialViewLocationFormats = base.ViewLocationFormats;
        }

         2:WebFormViewEngine有两个重要方法：FindPartialView以及FindView。它负责从用户请求以及路由配置中查找到具体的view page或者是partial view。第二点就可以在这下手。
         首先：我们需要修改下路由配置，增加一个参数viewpath,用来指定路由规则使用的view path路径。
      

routes.MapRoute(
                "Default2",
                "ViewContentPage1.aspx",
                new { id = "", viewpath = "~/com/ViewContentPage1.aspx", controller = "test", action = "test" }
            );

        其次：修改下WebFormViewEngine的源码：这里主要是修改GetPath方法，它最终会返回一个view page的路径。这样我们就可以这样访问了http://www.testmy.com/guestbook/ViewContentPage1.aspx。
      

public override ViewEngineResult FindPartialView(ControllerContext controllerContext, string partialViewName, bool useCache)
        {
            string[] strArray;
            if (controllerContext == null)
            {
                throw new ArgumentNullException("controllerContext");
            }
            if (string.IsNullOrEmpty(partialViewName))
            {
                throw new ArgumentException("MvcResources.Common_NullOrEmpty", "partialViewName");
            }
            string requiredString = controllerContext.RouteData.GetRequiredString("controller");
            //string vp = this.GetParam(controllerContext, "viewpath");
            //if (!string.IsNullOrEmpty(vp))
            //{
            //    requiredString = vp;
            //}
            string str2 = this.GetPath(controllerContext, this.PartialViewLocationFormats, "PartialViewLocationFormats", partialViewName, requiredString, "Partial", 

useCache,false , out strArray);
            if (string.IsNullOrEmpty(str2))
            {
                return new ViewEngineResult(strArray);
            }
            return new ViewEngineResult(this.CreatePartialView(controllerContext, str2), this);

        }
        public override ViewEngineResult FindView(ControllerContext controllerContext, string viewName, string masterName, bool useCache)
        {
            string[] strArray;
            string[] strArray2;
            if (controllerContext == null)
            {
                throw new ArgumentNullException("controllerContext");
            }
            if (string.IsNullOrEmpty(viewName))
            {
                throw new ArgumentException("ArgumentException", "viewName");
            }
            string requiredString = controllerContext.RouteData.GetRequiredString("controller");
            //string vp=this.GetParam(controllerContext, "viewpath");
            //if (!string.IsNullOrEmpty(vp))
            //{
            //    requiredString = vp;
            //}
            string str2 = this.GetPath(controllerContext, this.ViewLocationFormats, "ViewLocationFormats", viewName, requiredString, "View", useCache,true , out strArray);
            string str3 = this.GetPath(controllerContext, this.MasterLocationFormats, "MasterLocationFormats", masterName, requiredString, "Master", useCache,true , out 

strArray2);
            if (string.IsNullOrEmpty(str2) || (string.IsNullOrEmpty(str3) && !string.IsNullOrEmpty(masterName)))
            {
                return new ViewEngineResult(strArray.Union<string>(strArray2));
            }
            return new ViewEngineResult(this.CreateView(controllerContext, str2, str3), this);

        }
        private string GetParam(ControllerContext controllerContext, string key)
        {
            return controllerContext.RouteData.Values[key] != null ? controllerContext.RouteData.Values[key].ToString() : string.Empty;
        }
        private string GetPath(ControllerContext controllerContext, string[] locations, string locationsPropertyName, string name, string controllerName, string cacheKeyPrefix, 

bool useCache, bool isfindview, out string[] searchedLocations)
        {
            searchedLocations = _emptyLocations;
            if (string.IsNullOrEmpty(name))
            {
                return string.Empty;
            }
            if ((locations == null) || (locations.Length == 0))
            {
                throw new InvalidOperationException(string.Format(CultureInfo.CurrentUICulture, "MvcResources.Common_PropertyCannotBeNullOrEmpty", new object[] { 

locationsPropertyName }));
            }
            bool flag = IsSpecificPath(name);
            string key = this.CreateCacheKey(cacheKeyPrefix, name, flag ? string.Empty : controllerName);
            if (useCache)
            {
                string viewLocation = this.ViewLocationCache.GetViewLocation(controllerContext.HttpContext, key);
                if (viewLocation != null)
                {
                    return viewLocation;
                }
            }
            
            return (flag ? this.GetPathFromSpecificName(controllerContext, name, key,isfindview , ref searchedLocations) : this.GetPathFromGeneralName(controllerContext, 

locations, name, controllerName, key,isfindview , ref searchedLocations));
        }
        private string CreateCacheKey(string prefix, string name, string controllerName)
        {
            return string.Format(CultureInfo.InvariantCulture, ":ViewCacheEntry:{0}:{1}:{2}:{3}:", new object[] { base.GetType().AssemblyQualifiedName, prefix, name, 

controllerName });
        }
        private static bool IsSpecificPath(string name)
        {
            char ch = name[0];
            return ((ch == '~') || (ch == '/'));
        }
        private string GetPathFromSpecificName(ControllerContext controllerContext, string name, string cacheKey,bool isfindview, ref string[] searchedLocations)
        {
            string virtualPath = name;
            if (!this.FileExists(controllerContext, name))
            {
                if (isfindview)
                {
                    string vp = this.GetParam(controllerContext, "viewpath");
                    if (!string.IsNullOrEmpty(vp))
                    {
                        virtualPath = vp;
                    }
                    if (string.IsNullOrEmpty(virtualPath))
                    {
                        virtualPath = string.Empty;
                        searchedLocations = new string[] { name };
                    }
                }
                else
                {
                    virtualPath = string.Empty;
                    searchedLocations = new string[] { name };
 
                }
            }
            this.ViewLocationCache.InsertViewLocation(controllerContext.HttpContext, cacheKey, virtualPath);
            return virtualPath;
        }
        private string GetPathFromGeneralName(ControllerContext controllerContext, string[] locations, string name, string controllerName, string cacheKey, bool isfindview, ref 

string[] searchedLocations)
        {
            string virtualPath = string.Empty;
            searchedLocations = new string[locations.Length];
            for (int i = 0; i < locations.Length; i++)
            {
                string str2 = string.Format(CultureInfo.InvariantCulture, locations[i], new object[] { name, controllerName });
                if (this.FileExists(controllerContext, str2))
                {
                    searchedLocations = _emptyLocations;
                    virtualPath = str2;
                    this.ViewLocationCache.InsertViewLocation(controllerContext.HttpContext, cacheKey, virtualPath);
                    return virtualPath;
                }
                else
                {
                    if (isfindview)
                    {
                        string vp = this.GetParam(controllerContext, "viewpath");
                        if (!string.IsNullOrEmpty(vp))
                        {
                            searchedLocations = _emptyLocations;
                            virtualPath = vp;
                            return virtualPath;
                        }
                    }

                }
                searchedLocations[i] = str2;
            }
            return virtualPath;
        }

           最后：在程序中注册新的view engine:        

            //注册viewEngine
            ViewEngines.Engines.Clear();
            ViewEngines.Engines.Add(new WebViewEngine());
            RegisterRoutes(RouteTable.Routes);

           总结：很久没有更新mvc的文章了,不过这篇在实际项目中还是非常有用的，例如，我们可以把两个不同的view page指定同一个Controller等等。

作者：姜敏
出处：http://www.cnblogs.com/aspnet2008/