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Web开发学习心得7MasterPage的实现原理MasterPage是A2.0引入的一个非常实用的特性，怎么用，我想不用我说，基本上大家都会，这里要讲的是，它是如何实现的。 在深入源代码去探索MasterPage之前，我以为MasterPage的实现应该是比较复杂的，也一直纳闷为什么MasterPage类会继承于UserControl类，感觉这两者好像差得很远。昨天晚上，我专门抽出时间，阅读了部分与MasterPage有关的源代码，终于明白了是怎么回事，在那突然明白的那一刻，真有如醍醐灌顶，拍案叫绝，不得不佩服微软的那些guys。 下面就是我的探索之旅的过程（大家也可以跳过该部分，直接看后面的真相大白部分）： 1、我首先查看的是Page.ProcessRequestMain方法，我们知道，Page类大部分特性，包括LifeCycle、PostBack、ProcessPostData等都是在该方法中实现，所以，我想，MasterPage的实现肯定在该方法中有不少的体现。然而，令我惊讶的是，我居然没有在该方法中找到任何有关MasterPage的线索，而仅仅在this.PerformPreInit()中，找到唯一一个ApplyMasterPage()方法。而该方法也出奇的简单，感觉仅仅是将递归的各级MasterPage的._masterPageApplied字段设为true而已。当时，我忽略了一个重要的东西，就是代码中对this.Master这个属性的访问，实际上，奥秘就在对这个属性的访问上（下文将叙述）。private void PerformPreInit() this.OnPreInit(EventArgs.Empty); this.InitializeThemes(); this.ApplyMasterPage(); this._preInitWorkComplete = true;Page.ApplyMasterPage()private void ApplyMasterPage() if (this.Master != null) ArrayList appliedMasterFilePaths = new ArrayList(); appliedMasterFilePaths.Add(this._masterPageFile.VirtualPathString.ToLower(CultureInfo.InvariantCulture); MasterPage.ApplyMasterRecursive(this.Master, appliedMasterFilePaths); 2、我查看了MasterPage的源代码，出奇的是，竟也如此简单，以至于我也没有从该源代码中找到多少有价值的信息。MasterPageControlBuilder(typeof(MasterPageControlBuilder), Designer(Microsoft.VisualStudio.Web.WebForms.MasterPageWebFormDesigner, Microsoft.VisualStudio.Web, Version=, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a, typeof(IRootDesigner), ParseChildren(false), AspNetHostingPermission(SecurityAction.LinkDemand, Level=AspNetHostingPermissionLevel.Minimal), AspNetHostingPermission(SecurityAction.InheritanceDemand, Level=AspNetHostingPermissionLevel.Minimal)public class MasterPage : UserControl private IList _contentPlaceHolders; private IDictionary _contentTemplateCollection; private IDictionary _contentTemplates; private MasterPage _master; private bool _masterPageApplied; private VirtualPath _masterPageFile; internal TemplateControl _ownerControl; EditorBrowsable(EditorBrowsableState.Advanced) protected internal void AddContentTemplate(string templateName, ITemplate template) if (this._contentTemplateCollection = null) this._contentTemplateCollection = new Hashtable(10, StringComparer.OrdinalIgnoreCase); try this._contentTemplateCollection.Add(templateName, template); catch (ArgumentException) throw new HttpException(SR.GetString(MasterPage_Multiple_content, new object templateName ); internal static void ApplyMasterRecursive(MasterPage master, IList appliedMasterFilePaths) if (master.Master != null) string str = master._masterPageFile.VirtualPathString.ToLower(CultureInfo.InvariantCulture); if (appliedMasterFilePaths.Contains(str) throw new InvalidOperationException(SR.GetString(MasterPage_Circular_Master_Not_Allowed, new object master._masterPageFile ); appliedMasterFilePaths.Add(str); ApplyMasterRecursive(master.Master, appliedMasterFilePaths); master._masterPageApplied = true; internal static MasterPage CreateMaster(TemplateControl owner, HttpContext context, VirtualPath masterPageFile, IDictionary contentTemplateCollection) MasterPage child = null; if (masterPageFile = null) if (contentTemplateCollection != null) & (contentTemplateCollection.Count 0) throw new HttpException(SR.GetString(Content_only_allowed_in_content_page); return null; VirtualPath virtualPath = VirtualPathProvider.CombineVirtualPathsInternal(owner.TemplateControlVirtualPath, masterPageFile); ITypedWebObjectFactory vPathBuildResult = (ITypedWebObjectFactory) BuildManager.GetVPathBuildResult(context, virtualPath); if (!typeof(MasterPage).IsAssignableFrom(vPathBuildResult.InstantiatedType) throw new HttpException(SR.GetString(Invalid_master_base, new object masterPageFile ); child = (MasterPage) vPathBuildResult.CreateInstance(); child.TemplateControlVirtualPath = virtualPath; if (owner.HasControls() foreach (Control control in owner.Controls) LiteralControl control2 = control as LiteralControl; if (control2 = null) | (Util.FirstNonWhiteSpaceIndex(control2.Text) = 0) throw new HttpException(SR.GetString(Content_allowed_in_top_level_only); owner.Controls.Clear(); if (owner.Controls.IsReadOnly) throw new HttpException(SR.GetString(MasterPage_Cannot_ApplyTo_ReadOnly_Collection); if (contentTemplateCollection != null) foreach (string str in contentTemplateCollection.Keys) if (!child.ContentPlaceHolders.Contains(str.ToLower(CultureInfo.InvariantCulture) throw new HttpException(SR.GetString(MasterPage_doesnt_have_contentplaceholder, new object str, masterPageFile ); child._contentTemplates = contentTemplateCollection; child._ownerControl = owner; child.InitializeAsUserControl(owner.Page); owner.Controls.Add(child); return child; Browsable(false), EditorBrowsable(EditorBrowsableState.Advanced) protected internal IList ContentPlaceHolders get if (this._contentPlaceHolders = null) this._contentPlaceHolders = new ArrayList(); return this._contentPlaceHolders; Browsable(false), EditorBrowsable(EditorBrowsableState.Advanced) protected internal IDictionary ContentTemplates get return this._contentTemplates; WebSysDescription(MasterPage_MasterPage), DesignerSerializationVisibility(DesignerSerializationVisibility.Hidden), Browsable(false) public MasterPage Master get if (this._master = null) & !this._masterPageApplied) this._master = CreateMaster(this, this.Context, this._masterPageFile, this._contentTemplateCollection); return this._master; WebSysDescription(MasterPage_MasterPageFile), WebCategory(Behavior), DefaultValue() public string MasterPageFile get return VirtualPath.GetVirtualPathString(this._masterPageFile); set if (this._masterPageApplied) throw new InvalidOperationException(SR.GetString(PropertySetBeforePageEvent, new object MasterPageFile, Page_PreInit ); if (value != VirtualPath.GetVirtualPathString(this._masterPageFile) this._masterPageFile = VirtualPath.CreateAllowNull(value); if (this._master != null) & this.Controls.Contains(this._master) this.Controls.Remove(this._master); this._master = null; 3、我又查看了ContentPlaceHolder类、Content类，心想，难道奥秘在这两个控件上？打开源代码一看，彻底晕倒，这两个类简单得简直不能让人相信，ContentPlaceHolder居然是一个空类，仅仅起到一个标识的作用，而Content居然也仅仅只有ContentPlaceHolderID唯一一个string属性。public class ContentPlaceHolder : Control, INonBindingContainer, INamingContainerContentpublic class Content : Control, INonBindingContainer, INamingContainer private string _contentPlaceHolderID; public string ContentPlaceHolderID get if (this._contentPlaceHolderID = null) return string.Empty; return this._contentPlaceHolderID; set if (!base.DesignMode) throw new NotSupportedException(SR.GetString(Property_Set_Not_Supported, new object ContentPlaceHolderID, base.GetType().ToString() ); this._contentPlaceHolderID = value; 4、此时，我几乎已经没法再从A源代码中找到其他有关MasterPage的有价值的信息了。于是，我决定写一个简单的Web应用程序，该应用程序仅仅只有一个MasterPage页与Default页，并将其编译，查看编译后的代码，看看是否能找到有价值的信息。 源代码如下：MasterPage.master Default.aspx 编译后代码如下：CompilerGlobalScopepublic class masterpage_master : MasterPage private static bool _initialized; private ITemplate _Template_ContentPlaceHolder; protected ContentPlaceHolder ContentPlaceHolder; protected HtmlForm form1; protected Button master; DebuggerNonUserCode public masterpage_master() base.AppRelativeVirtualPath = /MasterPage.master; if (!_initialized) _initialized = true; base.ContentPlaceHolders.Add(contentplaceholder); DebuggerNonUserCode private ContentPlaceHolder _BuildControlContentPlaceHolder() ContentPlaceHolder container = new ContentPlaceHolder(); this.ContentPlaceHolder = container; container.ID = ContentPlaceHolder; if (base.ContentTemplates != null) this._Template_ContentPlaceHolder = (ITemplate) base.ContentTemplatesContentPlaceHolder; if (this._Template_ContentPlaceHolder != null) this._Template_ContentPlaceHolder.InstantiateIn(container); return container; IParserAccessor accessor = container; accessor.AddParsedSubObject(new LiteralControl(rn ); Button button = this._BuildControlmaster(); accessor.AddParsedSubObject(button); accessor.AddParsedSubObject(new LiteralControl(rn ); return container; DebuggerNonUserCode private HtmlForm _BuildControlform1() HtmlForm form = new HtmlForm(); this.form1 = form; form.ID = form1; IParserAccessor accessor = form; accessor.AddParsedSubObject(new LiteralControl(rn rn ); ContentPlaceHolder holder = this._BuildControlContentPlaceHolder(); accessor.AddParsedSubObject(holder); accessor.AddParsedSubObject(new LiteralControl(rn rn ); return form; DebuggerNonUserCode private Button _BuildControlmaster() Button button = new Button(); this.master = button; button.ApplyStyleSheetSkin(this.Page); button.ID = master; button.Text = master; return button; DebuggerNonUserCode private void _BuildControlTree(masterpage_master _ctrl) IParserAccessor accessor = _ctrl; accessor.AddParsedSubObject(new LiteralControl(rnrnrnrnrnrn rnrnrn ); HtmlForm form = this._BuildControlform1(); accessor.AddParsedSubObject(form); accessor.AddParsedSubObject(new LiteralControl(rnrnrn); DebuggerNonUserCode protected override void FrameworkInitialize() base.FrameworkInitialize(); this._BuildControlTree(this); protected HttpApplication ApplicationInstance get return this.Context.ApplicationInstance; protected DefaultProfile Profile get return (DefaultProfile) this.Context.Profile; protected override bool SupportAutoEvents get return false; TemplateContainer(typeof(MasterPage), TemplateInstance(TemplateInstance.Single) public virtual ITemplate Template_ContentPlaceHolder get return this._Template_ContentPlaceHolder; set this._Template_ContentPlaceHolder = value; CodeCompilerGlobalScopepublic class default_aspx : Page, IRequiresSessionState, IHttpHandler private static object _fileDependencies; private static bool _initialized; protected Button default; DebuggerNonUserCode public default_aspx() base.AppRelativeVirtualPath = /Default.aspx; if (!_initialized) string virtualFileDependencies = new string /Default.aspx, /MasterPage.master ; _fileDependencies = base.GetWrappedFileDependencies(virtualFileDependencies); _initialized = true; base.Server.ScriptTimeout = 0x1c9c380; DebuggerNonUserCode private void _BuildControlContent(Control _ctrl) IParserAccessor accessor = _ctrl; accessor.AddParsedSubObject(new LiteralControl(rn ); Button button = this._BuildControldefault(); accessor.AddParsedSubObject(button); accessor.AddParsedSubObject(new LiteralControl(rn); DebuggerNonUserCode private Button _BuildControldefault() Button button = new Button(); this.default = button; button.TemplateControl = this; button.ApplyStyleSheetSkin(this); button.ID = default; button.Text = default; return button; DebuggerNonUserCode private void _BuildControlTree(default_aspx _ctrl) _ctrl.Title = ; _ctrl.MasterPageFile = /MasterPage.master; this.InitializeCulture(); base.AddContentTemplate(ContentPlaceHolder, new CompiledTemplateBuilder(new BuildTemplateMethod(this._BuildControlContent); IParserAccessor accessor = _ctrl; accessor.AddParsedSubObject(new LiteralControl(rnrn); DebuggerNonUserCode protected override void FrameworkInitialize() base.FrameworkInitialize(); this._BuildControlTree(this); base.AddWrappedFileDependencies(_fileDependencies); base.Request.ValidateInput(); DebuggerNonUserCode public override int GetTypeHashCode() return -2002306427; DebuggerNonUserCode public override void ProcessRequest(HttpContext context) base.ProcessRequest(context); protected HttpApplication ApplicationInstance get return this.Context.ApplicationInstance; public masterpage_master Master get return (masterpage_master) base.Master; protected DefaultProfile Profile get return (DefaultProfile) this.Context.Profile; protected override bool SupportAutoEvents get return false; 我们首先观察default_aspx的BuildControlTree方法，该方法调用了base.AddContentTemplate(ContentPlaceHolder, new CompiledTemplateBuilder(new BuildTemplateMethod(this._BuildControlContent);而该方法实质上只有一行代码，即this._contentTemplateCollection.Add(templateName, template);其中，_contentTemplateCollection是IDictionary类型。因此，base.AddContentTemplate只有一个功能，即在Page的_contentTemplateCollection中添加一个CompliedTemplateBuilder类型的对象。那么该对象有啥作用呢？为了不岔开话题，这里不对该对象做详细描述，只给出结论：该对象实现ITemplate接口，其接口方法InstantiateIn(Control container)具体实现为为container添加BuildTemplateMethod委托所创建的控件。这话有点拗口，简单地就刚才那个例子来说，就是如果你调用该对象的InstantiateIn(Control container)方法，就为该container添加this._BuildControlContent()方法所创建的控件做为子控件。 5、我们继续来看看masterpage_master的_BuildControlContentPlaceHolder()方法，我们发现，该方法即调用了刚才讨论的那个InstantiateIn方法。哈，原来在这里，终于明白了，原来Page里Content控件中的所有内容最终都将变成其对应的MasterPage中的ContentPlaceHolder的子控件。等一下，这个结论下得有点早，难道这里的base.ContentTemplates属性就等于Page的_contentTemplateCollection字段吗？如果是，那么上面的结论就是正确的。 6、我们重新回到1中的代码，查看Page.Master属性的实现，我们发现，它调用了MasterPage的CreateMaster静态方法，