ASP.NET MVC 4 視圖頁去哪裏兒
這裏特別感謝 swagon 提到了Displaymodeprovider，因此纔有了本篇博客，也使我對【View的呈現】中尋找視圖頁的過程有了清晰的認識！html
前戲
在MVC中，執行完Action以後，會返回一個ActionResult對象，以後再執行該對象的ExecuteResult方法，這也就是【View的呈現】的入口！ios
【View的呈現】包括了：根據模版去尋找請求的視圖頁、編譯視圖頁、再執行視圖頁的內容。本篇就來介紹尋找視圖頁的詳細過程，其中涉及到了MVC 4的一個新特性--「手機視圖頁」緩存
public abstract class ViewResultBase : ActionResult
{
public override void ExecuteResult(ControllerContext context)
{
if (context == null)
{
throw new ArgumentNullException("context");
}
if (String.IsNullOrEmpty(ViewName))
{
ViewName = context.RouteData.GetRequiredString("action");
}
ViewEngineResult result = null;
if (View == null)
{
//經過視圖引擎去建立視圖對象，並將視圖對象和該視圖相關的信息封裝在ViewEngineResult對象中。
result = FindView(context);
View = result.View;
}
TextWriter writer = context.HttpContext.Response.Output;
ViewContext viewContext = new ViewContext(context, View, ViewData, TempData, writer);
View.Render(viewContext, writer);
if (result != null)
{
result.ViewEngine.ReleaseView(context, View);
}
}
}
public class ViewResult : ViewResultBase
{
protected override ViewEngineResult FindView(ControllerContext context)
{
//尋找當前請求的視圖頁，若是能找到則建立視圖對象。
//遍歷每一個視圖引擎（默認有兩個WebFormEngine、RazorViewEngine），並執行每個視圖引擎的FindView方法。
ViewEngineResult result = ViewEngineCollection.FindView(context, ViewName, MasterName);
//若是建立了視圖對象，即：指定路徑中存在相匹配的視圖頁（.cshtml文件）。
if (result.View != null)
{
return result;
}
//沒有建立視圖對象，即：指定路徑中不存在相匹配的視圖頁（.cshtml文件）。
StringBuilder locationsText = new StringBuilder();
foreach (string location in result.SearchedLocations)
{
locationsText.AppendLine();
locationsText.Append(location);
}
throw new InvalidOperationException(String.Format(CultureInfo.CurrentCulture,
MvcResources.Common_ViewNotFound, ViewName, locationsText));
}
}
ViewEngineResult result = ViewEngineCollection.FindView(context, ViewName, MasterName);則是遍歷每一個視圖引擎（默認有兩個WebFormEngine、RazorViewEngine），並執行每個視圖引擎的FindView方法。
注：在執行視圖引擎的FindView方法時，先按照從緩存表中找是否存在請求的視圖頁，若是沒有的話，再進行一次尋找！app
下面以RazorViewEngine爲例：ide
public abstract class VirtualPathProviderViewEngine : IViewEngine
{
//useCache先是true，該方法返回的是null。則讓useCache=false，再執行一遍。即：先經過緩存去找，若是沒有找到的話，就正經的去找。
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");
//獲取視圖的路徑，這裏就是我們本篇博文的內容的入口點！！！！！！！！！！！！！！！！！！！
//ViewLocationFormats、AreaViewLocationFormats定義在派生類RazorViewEngine類中。
//ViewLocationFormats："~/Views/{1}/{0}.cshtml","~/Views/{1}/{0}.vbhtml", "~/Views/Shared/{0}.cshtml","~/Views/Shared/{0}.vbhtml"
//AreaViewLocationFormats："~/Areas/{2}/Views/{1}/{0}.cshtml", "~/Areas/{2}/Views/{1}/{0}.vbhtml", "~/Areas/{2}/Views/Shared/{0}.cshtml","~/Areas/{2}/Views/Shared/{0}.vbhtml"
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);
}
}
啪啪啪
GetPath方法在尋找【視圖頁】時，首先將當前請求的Controller和Action的名稱添加到地址格式化器中，這樣就有了要尋找的地址（們），以後就來檢查格式化後的地址是否真的存在指定的【視圖頁】。若是是經過手機端來請求，則會對格式化以後的地址進行再進行處理（如：Index.cshtml修改成Index.Mobile.cshtml）,以後再檢查新地址下是否存在【視圖頁】。函數
注：默認狀況下會先檢查是否爲手機端訪問！ui
口說無憑，上源碼吧：this
// Copyright (c) Microsoft Open Technologies, Inc. All rights reserved. See License.txt in the project root for license information. using System.Collections.Generic; using System.Diagnostics.CodeAnalysis; using System.Globalization; using System.Linq; using System.Web.Hosting; using System.Web.Mvc.Properties; using System.Web.WebPages; namespace System.Web.Mvc { public abstract class VirtualPathProviderViewEngine : IViewEngine { // format is ":ViewCacheEntry:{cacheType}:{prefix}:{name}:{controllerName}:{areaName}:" private const string CacheKeyFormat = ":ViewCacheEntry:{0}:{1}:{2}:{3}:{4}:"; private const string CacheKeyPrefixMaster = "Master"; private const string CacheKeyPrefixPartial = "Partial"; private const string CacheKeyPrefixView = "View"; private static readonly string[] _emptyLocations = new string[0]; private DisplayModeProvider _displayModeProvider; private Func<VirtualPathProvider> _vppFunc = () => HostingEnvironment.VirtualPathProvider; internal Func<string, string> GetExtensionThunk = VirtualPathUtility.GetExtension; private IViewLocationCache _viewLocationCache; [SuppressMessage("Microsoft.Performance", "CA1819:PropertiesShouldNotReturnArrays", Justification = "This is a shipped API")] public string[] AreaMasterLocationFormats { get; set; } [SuppressMessage("Microsoft.Performance", "CA1819:PropertiesShouldNotReturnArrays", Justification = "This is a shipped API")] public string[] AreaPartialViewLocationFormats { get; set; } [SuppressMessage("Microsoft.Performance", "CA1819:PropertiesShouldNotReturnArrays", Justification = "This is a shipped API")] public string[] AreaViewLocationFormats { get; set; } [SuppressMessage("Microsoft.Performance", "CA1819:PropertiesShouldNotReturnArrays", Justification = "This is a shipped API")] public string[] FileExtensions { get; set; } [SuppressMessage("Microsoft.Performance", "CA1819:PropertiesShouldNotReturnArrays", Justification = "This is a shipped API")] public string[] MasterLocationFormats { get; set; } [SuppressMessage("Microsoft.Performance", "CA1819:PropertiesShouldNotReturnArrays", Justification = "This is a shipped API")] public string[] PartialViewLocationFormats { get; set; } // Neither DefaultViewLocationCache.Null nor a DefaultViewLocationCache instance maintain internal state. Fine // if multiple threads race to initialize _viewLocationCache. public IViewLocationCache ViewLocationCache { get { if (_viewLocationCache == null) { if (HttpContext.Current == null || HttpContext.Current.IsDebuggingEnabled) { _viewLocationCache = DefaultViewLocationCache.Null; } else { _viewLocationCache = new DefaultViewLocationCache(); } } return _viewLocationCache; } set { if (value == null) { throw Error.ArgumentNull("value"); } _viewLocationCache = value; } } [SuppressMessage("Microsoft.Performance", "CA1819:PropertiesShouldNotReturnArrays", Justification = "This is a shipped API")] public string[] ViewLocationFormats { get; set; } // Likely exists for testing only protected VirtualPathProvider VirtualPathProvider { get { return _vppFunc(); } set { if (value == null) { throw Error.ArgumentNull("value"); } _vppFunc = () => value; } } // Provided for testing only; setter used in BuildManagerViewEngine but only for test scenarios internal Func<VirtualPathProvider> VirtualPathProviderFunc { get { return _vppFunc; } set { if (value == null) { throw Error.ArgumentNull("value"); } _vppFunc = value; } } protected internal DisplayModeProvider DisplayModeProvider { get { return _displayModeProvider ?? DisplayModeProvider.Instance; } set { _displayModeProvider = value; } } internal virtual string CreateCacheKey(string prefix, string name, string controllerName, string areaName) { return String.Format(CultureInfo.InvariantCulture, CacheKeyFormat, GetType().AssemblyQualifiedName, prefix, name, controllerName, areaName); } internal static string AppendDisplayModeToCacheKey(string cacheKey, string displayMode) { // key format is ":ViewCacheEntry:{cacheType}:{prefix}:{name}:{controllerName}:{areaName}:" // so append "{displayMode}:" to the key return cacheKey + displayMode + ":"; } protected abstract IView CreatePartialView(ControllerContext controllerContext, string partialPath); protected abstract IView CreateView(ControllerContext controllerContext, string viewPath, string masterPath); protected virtual bool FileExists(ControllerContext controllerContext, string virtualPath) { return VirtualPathProvider.FileExists(virtualPath); } public virtual ViewEngineResult FindPartialView(ControllerContext controllerContext, string partialViewName, bool useCache) { if (controllerContext == null) { throw new ArgumentNullException("controllerContext"); } if (String.IsNullOrEmpty(partialViewName)) { throw new ArgumentException(MvcResources.Common_NullOrEmpty, "partialViewName"); } string[] searched; string controllerName = controllerContext.RouteData.GetRequiredString("controller"); string partialPath = GetPath(controllerContext, PartialViewLocationFormats, AreaPartialViewLocationFormats, "PartialViewLocationFormats", partialViewName, controllerName, CacheKeyPrefixPartial, useCache, out searched); if (String.IsNullOrEmpty(partialPath)) { return new ViewEngineResult(searched); } return new ViewEngineResult(CreatePartialView(controllerContext, partialPath), this); } //開始開始開始開始開始開始開始開始開始開始開始開始開始開始開始開始開始開始開始開始 //useCache先是true，該方法返回的是null。則讓useCache=false，再執行一遍。即：先經過緩存去找，若是沒有找到的話，就正經的去找。 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"); //獲取視圖的路徑 //ViewLocationFormats、AreaViewLocationFormats定義在派生類RazorViewEngine類中。 //ViewLocationFormats："~/Views/{1}/{0}.cshtml","~/Views/{1}/{0}.vbhtml", "~/Views/Shared/{0}.cshtml","~/Views/Shared/{0}.vbhtml" //AreaViewLocationFormats："~/Areas/{2}/Views/{1}/{0}.cshtml", "~/Areas/{2}/Views/{1}/{0}.vbhtml", "~/Areas/{2}/Views/Shared/{0}.cshtml","~/Areas/{2}/Views/Shared/{0}.vbhtml" 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); } //獲取視圖路徑方法 private string GetPath(ControllerContext controllerContext, string[] locations, string[] areaLocations, string locationsPropertyName, string name, string controllerName, string cacheKeyPrefix, bool useCache, out string[] searchedLocations) { searchedLocations = _emptyLocations; if (String.IsNullOrEmpty(name)) { return String.Empty; } //從RouteData的DataTokens中獲取key爲‘area’的值 string areaName = AreaHelpers.GetAreaName(controllerContext.RouteData); bool usingAreas = !String.IsNullOrEmpty(areaName); // List<ViewLocation> viewLocations = GetViewLocations(locations, (usingAreas) ? areaLocations : null); if (viewLocations.Count == 0) { throw new InvalidOperationException(String.Format(CultureInfo.CurrentCulture, MvcResources.Common_PropertyCannotBeNullOrEmpty, locationsPropertyName)); } bool nameRepresentsPath = IsSpecificPath(name); string cacheKey = CreateCacheKey(cacheKeyPrefix, name, (nameRepresentsPath) ? String.Empty : controllerName, areaName); //是否使用緩存，其實就將一個已知的路徑保存在緩存表中，若是是第一次請求，緩存表中什麼也麼有啊，因此暫且不看它。 if (useCache) { //根據請求上下文獲取可用的DisplayModelProvider IEnumerable<IDisplayMode> possibleDisplayModes = DisplayModeProvider.GetAvailableDisplayModesForContext(controllerContext.HttpContext, controllerContext.DisplayMode); foreach (IDisplayMode displayMode in possibleDisplayModes) { //displayMode.DisplayModeId就是「Mobile」，即：執行DefaultDisplayMode有參數的構造函數 string cachedLocation = ViewLocationCache.GetViewLocation(controllerContext.HttpContext, AppendDisplayModeToCacheKey(cacheKey, displayMode.DisplayModeId)); if (cachedLocation == null) { // If any matching display mode location is not in the cache, fall back to the uncached behavior, which will repopulate all of our caches. return null; } // A non-empty cachedLocation indicates that we have a matching file on disk. Return that result. if (cachedLocation.Length > 0) { if (controllerContext.DisplayMode == null) { controllerContext.DisplayMode = displayMode; } return cachedLocation; } // An empty cachedLocation value indicates that we don't have a matching file on disk. Keep going down the list of possible display modes. } // GetPath is called again without using the cache. return null; } else { //若是ViewResult的參數的第一個字符是：~ 或 /，則執行第一個方法，不然執行第二個方法！ //第一個方法：直接指定了路徑去尋找 //第二個方法：只經過試圖名稱再拼接路徑去尋找（用到了DisplayModeProvider） //第二個方法的viewLocations參數是含有8條數據的集合。 return nameRepresentsPath ? GetPathFromSpecificName(controllerContext, name, cacheKey, ref searchedLocations) : GetPathFromGeneralName(controllerContext, viewLocations, name, controllerName, areaName, cacheKey, ref searchedLocations); } } 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]; //根據8種格式器建立路徑 string virtualPath = location.Format(name, controllerName, areaName); //這裏的controllerContext.DisplayMode屬性執行DisplayModeProvider的GetDisplayMode、SetDisplayMode方法！ 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). //再執行循環執行除了適合的那個DefaultDisplayMode以外的全部DefaultDisplayMode對象，將全部存在的路徑封裝到DisplayInfo對象中，並添加到緩存表中，以便以後請求時直接去緩存中獲取。 //例如：當前是手機的請求，則會經過執行DisplayModeId=‘Mobile’的那個DefaultDisplayMode來獲取【視圖頁】的路徑（Index.Mobile.cshtml）， // 可是在執行完成以後，還會執行DisplayModeId!=‘Mobile’全部其餘的DefaultDisplayMode對象，也就是pc端請求時的路徑（Index.cshtml），將其加入緩存表中，以便下次請求時直接去緩存表中獲取。 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; } private string GetPathFromSpecificName(ControllerContext controllerContext, string name, string cacheKey, ref string[] searchedLocations) { string result = name; if (!(FilePathIsSupported(name) && FileExists(controllerContext, name))) { result = String.Empty; searchedLocations = new[] { name }; } ViewLocationCache.InsertViewLocation(controllerContext.HttpContext, cacheKey, result); return result; } private bool FilePathIsSupported(string virtualPath) { if (FileExtensions == null) { // legacy behavior for custom ViewEngine that might not set the FileExtensions property return true; } else { // get rid of the '.' because the FileExtensions property expects extensions withouth a dot. string extension = GetExtensionThunk(virtualPath).TrimStart('.'); return FileExtensions.Contains(extension, StringComparer.OrdinalIgnoreCase); } } private static List<ViewLocation> GetViewLocations(string[] viewLocationFormats, string[] areaViewLocationFormats) { //將四個AreaAwareViewLocation和四個ViewLocation添加到 allLocations集合中！並返回 //AreaAwareViewLocation繼承自ViewLocation List<ViewLocation> allLocations = new List<ViewLocation>(); if (areaViewLocationFormats != null) { foreach (string areaViewLocationFormat in areaViewLocationFormats) { allLocations.Add(new AreaAwareViewLocation(areaViewLocationFormat)); } } if (viewLocationFormats != null) { foreach (string viewLocationFormat in viewLocationFormats) { allLocations.Add(new ViewLocation(viewLocationFormat)); } } return allLocations; } private static bool IsSpecificPath(string name) { char c = name[0]; return (c == '~' || c == '/'); } public virtual void ReleaseView(ControllerContext controllerContext, IView view) { IDisposable disposable = view as IDisposable; if (disposable != null) { disposable.Dispose(); } } private class AreaAwareViewLocation : ViewLocation { public AreaAwareViewLocation(string virtualPathFormatString) : base(virtualPathFormatString) { } public override string Format(string viewName, string controllerName, string areaName) { return String.Format(CultureInfo.InvariantCulture, _virtualPathFormatString, viewName, controllerName, areaName); } } private class ViewLocation { protected string _virtualPathFormatString; public ViewLocation(string virtualPathFormatString) { _virtualPathFormatString = virtualPathFormatString; } public virtual string Format(string viewName, string controllerName, string areaName) { return String.Format(CultureInfo.InvariantCulture, _virtualPathFormatString, viewName, controllerName); } } } }
// Copyright (c) Microsoft Open Technologies, Inc. All rights reserved. See License.txt in the project root for license information. using System.Collections.Generic; using System.Linq; namespace System.Web.WebPages { public sealed class DisplayModeProvider { public static readonly string MobileDisplayModeId = "Mobile"; public static readonly string DefaultDisplayModeId = String.Empty; private static readonly object _displayModeKey = new object(); private static readonly DisplayModeProvider _instance = new DisplayModeProvider(); //默認狀況下只有兩個DefaultDisplayMode，能夠自定義並添加到該集合中！ private readonly List<IDisplayMode> _displayModes = new List<IDisplayMode> { new DefaultDisplayMode(MobileDisplayModeId) { ContextCondition = context => context.GetOverriddenBrowser().IsMobileDevice }, new DefaultDisplayMode() }; internal DisplayModeProvider() { // The type is a psuedo-singleton. A user would gain nothing from constructing it since we won't use anything but DisplayModeProvider.Instance internally. } /// <summary> /// Restricts the search for Display Info to Display Modes either equal to or following the current /// Display Mode in Modes. For example, a page being rendered in the Default Display Mode will not /// display Mobile partial views in order to achieve a consistent look and feel. /// </summary> public bool RequireConsistentDisplayMode { get; set; } public static DisplayModeProvider Instance { get { return _instance; } } /// <summary> /// All Display Modes that are available to handle a request. /// </summary> public IList<IDisplayMode> Modes { get { return _displayModes; } } //這個方法的功能：若是指定集合中的某個DefaultDisplayMode來處理請求的話，則直接從它開始。能夠在HomeController中經過this.ControllerContext.DisplayMode來設置。 private int FindFirstAvailableDisplayMode(IDisplayMode currentDisplayMode, bool requireConsistentDisplayMode) { if (requireConsistentDisplayMode && currentDisplayMode != null) { //若是集合中麼有和當前currentDisplayMode匹配的話，first值爲 -1 int first = _displayModes.IndexOf(currentDisplayMode); return (first >= 0) ? first : _displayModes.Count; } return 0; } /// <summary> /// Returns any IDisplayMode that can handle the given request. /// </summary> public IEnumerable<IDisplayMode> GetAvailableDisplayModesForContext(HttpContextBase httpContext, IDisplayMode currentDisplayMode) { return GetAvailableDisplayModesForContext(httpContext, currentDisplayMode, RequireConsistentDisplayMode); } internal IEnumerable<IDisplayMode> GetAvailableDisplayModesForContext(HttpContextBase httpContext, IDisplayMode currentDisplayMode, bool requireConsistentDisplayMode) { int first = FindFirstAvailableDisplayMode(currentDisplayMode, requireConsistentDisplayMode); for (int i = first; i < _displayModes.Count; i++) { IDisplayMode mode = _displayModes[i]; if (mode.CanHandleContext(httpContext)) { yield return mode; } } } /// <summary> /// Returns DisplayInfo from the first IDisplayMode in Modes that can handle the given request and locate the virtual path. /// If currentDisplayMode is not null and RequireConsistentDisplayMode is set to true the search for DisplayInfo will only /// start with the currentDisplayMode. /// </summary> public DisplayInfo GetDisplayInfoForVirtualPath(string virtualPath, HttpContextBase httpContext, Func<string, bool> virtualPathExists, IDisplayMode currentDisplayMode) { //默認RequireConsistentDisplayMode爲false return GetDisplayInfoForVirtualPath(virtualPath, httpContext, virtualPathExists, currentDisplayMode, RequireConsistentDisplayMode); } internal DisplayInfo GetDisplayInfoForVirtualPath(string virtualPath, HttpContextBase httpContext, Func<string, bool> virtualPathExists, IDisplayMode currentDisplayMode, bool requireConsistentDisplayMode) { // Performance sensitive int first = FindFirstAvailableDisplayMode(currentDisplayMode, requireConsistentDisplayMode); for (int i = first; i < _displayModes.Count; i++) { IDisplayMode mode = _displayModes[i]; if (mode.CanHandleContext(httpContext)) { DisplayInfo info = mode.GetDisplayInfo(httpContext, virtualPath, virtualPathExists); if (info != null) { return info; } } } return null; } internal static IDisplayMode GetDisplayMode(HttpContextBase context) { return context != null ? context.Items[_displayModeKey] as IDisplayMode : null; } internal static void SetDisplayMode(HttpContextBase context, IDisplayMode displayMode) { if (context != null) { context.Items[_displayModeKey] = displayMode; } } } }
// Copyright (c) Microsoft Open Technologies, Inc. All rights reserved. See License.txt in the project root for license information. using System.IO; namespace System.Web.WebPages { public class DefaultDisplayMode : IDisplayMode { //經過構造函數賦值，MVC會建立兩個DefaultDisplayMode對象，將其中一個對象的該字段值設置爲「Mobile」 private readonly string _suffix; public DefaultDisplayMode() : this(DisplayModeProvider.DefaultDisplayModeId) { } public DefaultDisplayMode(string suffix) { _suffix = suffix ?? String.Empty; } public Func<HttpContextBase, bool> ContextCondition { get; set; } public virtual string DisplayModeId { get { return _suffix; } } public bool CanHandleContext(HttpContextBase httpContext) { return ContextCondition == null || ContextCondition(httpContext); } public virtual DisplayInfo GetDisplayInfo(HttpContextBase httpContext, string virtualPath, Func<string, bool> virtualPathExists) { //調用TransformPath方法，將尋找【View視圖頁】路徑設置爲 xxx.Mobile.cshtml string transformedFilename = TransformPath(virtualPath, _suffix); if (transformedFilename != null && virtualPathExists(transformedFilename)) { return new DisplayInfo(transformedFilename, this); } return null; } protected virtual string TransformPath(string virtualPath, string suffix) { if (String.IsNullOrEmpty(suffix)) { return virtualPath; } string extension = Path.GetExtension(virtualPath); return Path.ChangeExtension(virtualPath, suffix + extension); } } }
由以上源碼可知，默認狀況下，ASP.NET MVC4在DisplayModeProvider中定義了一個含有兩個DefaultDisplayMode對象（用於對地址再處理）的集合：spa
public static readonly string MobileDisplayModeId = "Mobile";
private readonly List<IDisplayMode> _displayModes = new List<IDisplayMode>
{
new DefaultDisplayMode(MobileDisplayModeId)
{
ContextCondition = context => context.GetOverriddenBrowser().IsMobileDevice
},
new DefaultDisplayMode()
};
因爲處理時，是按照遍歷執行_displayModes集合中DefaultDisplayMode對象的GetDisplayInfo方法（索引值從0開始），因此不管是 PC 仍是 Phone發送的請求，都會先執集合中的第一個DefaultDisplayMode對象（判斷是否爲手機的請求）。若是Phone端發送請求，會去尋找xxx.Mobile.cshtml，若是沒有的話，就繼續執行第二個DefaultDisplayMode對象，去尋找xxx.cshtml。若是是PC端發送請求，也是首先執行第一個DefaultDisplayMode對象，可是因爲不知足 context => context.GetOverriddenBrowser().IsMobileDevice 條件，因此仍是須要去執行第二個DefaultDisplayMode對象，去尋找xxx.cshtml。3d
擴展：
一、指定DisplayMode
模擬需求：對Phone端用戶的某個Action請求，返回電腦版網頁。
public ActionResult Index()
{
//一些判斷條件
this.ControllerContext.DisplayMode = DisplayModeProvider.Instance.Modes[1];
DisplayModeProvider.Instance.RequireConsistentDisplayMode = true;
return View();
}
根據上述設置，即便是Phone端的請求而且還存在Index.Mobile.cshtml文件，也會去執行Index.cshtml，即：實現Phone用戶訪問電腦版網頁。
二、自定義DisplayMode
模擬需求：爲Android 2.3用戶設置特定的頁面
先建立一個相似於Index.Android23.cshtml 的頁面，而後在Global.asax中作以下設置便可：
public class MvcApplication : System.Web.HttpApplication
{
protected void Application_Start()
{
AreaRegistration.RegisterAllAreas();
WebApiConfig.Register(GlobalConfiguration.Configuration);
FilterConfig.RegisterGlobalFilters(GlobalFilters.Filters);
RouteConfig.RegisterRoutes(RouteTable.Routes);
BundleConfig.RegisterBundles(BundleTable.Bundles);
AuthConfig.RegisterAuth();
DisplayModeProvider.Instance.Modes.Insert(0, new DefaultDisplayMode("Android23")
{
ContextCondition = (context => context.GetOverriddenUserAgent().IndexOf
("Android 2.3", StringComparison.OrdinalIgnoreCase) >= 0)
});
}
}
以上就是全部內容，若有不適之處，請指正！！！
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