我在MVC 4 source code中挖掘了一下之后找到了答案。
RazorViewEngine 派生自 BuildManagerViewEngine，而这个又派生自 VirtualPathProviderViewEngine。
实现方法FindView的是VirtualPathProviderViewEngine：
public virtual ViewEngineResult FindView(ControllerContext controllerContext, string viewName, string masterName, bool useCache)
{
if (controllerContext == null)
{
throw new ArgumentNullException("controllerContext");
}
if (String.IsNullOrEmpty(viewName))
{
throw new ArgumentException(MvcResources.Common_NullOrEmpty, "viewName");
}
string[] viewLocationsSearched;
string[] masterLocationsSearched;
string controllerName = controllerContext.RouteData.GetRequiredString("controller");
string viewPath = GetPath(controllerContext, ViewLocationFormats, AreaViewLocationFormats, "ViewLocationFormats", viewName, controllerName, CacheKeyPrefixView, useCache, out viewLocationsSearched);
string masterPath = GetPath(controllerContext, MasterLocationFormats, AreaMasterLocationFormats, "MasterLocationFormats", masterName, controllerName, CacheKeyPrefixMaster, useCache, out masterLocationsSearched);
if (String.IsNullOrEmpty(viewPath) || (String.IsNullOrEmpty(masterPath) && !String.IsNullOrEmpty(masterName)))
{
return new ViewEngineResult(viewLocationsSearched.Union(masterLocationsSearched));
}
return new ViewEngineResult(CreateView(controllerContext, viewPath, masterPath), this);
}
当视图路径还没有被缓存时，那里使用的GetPath方法会做这样的事情：
return nameRepresentsPath
? GetPathFromSpecificName(controllerContext, name, cacheKey, ref searchedLocations)
: GetPathFromGeneralName(controllerContext, viewLocations, name, controllerName, areaName, cacheKey, ref searchedLocations);
到达那里！有趣的方法是GetPathFromGeneralName，它试图为视图构建整个路径并检查该路径是否存在。该方法循环遍历在视图引擎中注册的每个视图位置，使用 对当前 HttpContext 有效 的显示模式更新视图路径，然后检查解析的路径是否存在。如果是，则已找到视图，将其分配给结果，缓存并返回结果路径。
private string GetPathFromGeneralName(ControllerContext controllerContext, List<ViewLocation> locations, string name, string controllerName, string areaName, string cacheKey, ref string[] searchedLocations)
{
string result = String.Empty;
searchedLocations = new string[locations.Count];
for (int i = 0; i < locations.Count; i++)
{
ViewLocation location = locations[i];
string virtualPath = location.Format(name, controllerName, areaName);
DisplayInfo virtualPathDisplayInfo = DisplayModeProvider.GetDisplayInfoForVirtualPath(virtualPath, controllerContext.HttpContext, path => FileExists(controllerContext, path), controllerContext.DisplayMode);
if (virtualPathDisplayInfo != null)
{
string resolvedVirtualPath = virtualPathDisplayInfo.FilePath;
searchedLocations = _emptyLocations;
result = resolvedVirtualPath;
ViewLocationCache.InsertViewLocation(controllerContext.HttpContext, AppendDisplayModeToCacheKey(cacheKey, virtualPathDisplayInfo.DisplayMode.DisplayModeId), result);
if (controllerContext.DisplayMode == null)
{
controllerContext.DisplayMode = virtualPathDisplayInfo.DisplayMode;
}
// Populate the cache for all other display modes. We want to cache both file system hits and misses so that we can distinguish
// in future requests whether a file's status was evicted from the cache (null value) or if the file doesn't exist (empty string).
IEnumerable<IDisplayMode> allDisplayModes = DisplayModeProvider.Modes;
foreach (IDisplayMode displayMode in allDisplayModes)
{
if (displayMode.DisplayModeId != virtualPathDisplayInfo.DisplayMode.DisplayModeId)
{
DisplayInfo displayInfoToCache = displayMode.GetDisplayInfo(controllerContext.HttpContext, virtualPath, virtualPathExists: path => FileExists(controllerContext, path));
string cacheValue = String.Empty;
if (displayInfoToCache != null && displayInfoToCache.FilePath != null)
{
cacheValue = displayInfoToCache.FilePath;
}
ViewLocationCache.InsertViewLocation(controllerContext.HttpContext, AppendDisplayModeToCacheKey(cacheKey, displayMode.DisplayModeId), cacheValue);
}
}
break;
}
searchedLocations[i] = virtualPath;
}
return result;
}
您可能已经注意到，我没有谈论带有以下注释的一段代码（为清晰起见重新格式化）：
// Populate the cache for all other display modes.
// We want to cache both file system hits and misses so that we can distinguish
// in future requests whether a file's status was evicted from the cache
// (null value) or if the file doesn't exist (empty string).
这（以及注释下方的代码:)）意味着一旦 MVC 4 从视图引擎中注册的视图位置找到第一个有效路径，它还将检查视图文件是否为所有存在未测试的其他显示模式，因此可以将信息包含在缓存中（尽管仅针对该视图位置，而不是视图引擎中可用的所有位置）。
另请注意，它如何将 lambda 传递给每个测试的显示模式，以检查该模式的文件是否存在：
DisplayInfo displayInfoToCache = displayMode.GetDisplayInfo(
controllerContext.HttpContext,
virtualPath,
virtualPathExists: path => FileExists(controllerContext, path));
这就解释了为什么当您覆盖 FileExists 时，它也会被调用以用于移动视图，即使它已经找到了非移动视图。
在任何情况下，显示模式都可以像添加它们一样被删除：通过在应用程序启动时更新 DisplayModes 集合。例如，移除 Mobile 显示模式，只保留默认且非特定的模式（您无法清除集合，否则将永远找不到视图）：
...
using System.Web.WebPages;
...
protected void Application_Start()
{
DisplayModeProvider.Instance.Modes.Remove(
DisplayModeProvider.Instance.Modes
.Single(m => m.DisplayModeId == "Mobile"));
答案很长，但希望它有意义！