dom/base/nsStubMutationObserver.h

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
   3 /* This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 /*
   8  * nsStubMutationObserver is an implementation of the nsIMutationObserver
   9  * interface (except for the methods on nsISupports) that is intended to be
  10  * used as a base class within the content/layout library.  All methods do
  11  * nothing.
  12  */
  13
  14 #ifndef nsStubMutationObserver_h_
  15 #define nsStubMutationObserver_h_
  16
  17 #include "nsTHashMap.h"
  18 #include "nsIMutationObserver.h"
  19
  20 /**
  21  * There are two advantages to inheriting from nsStubMutationObserver
  22  * rather than directly from nsIMutationObserver:
  23  *  1. smaller compiled code size (since there's no need for the code
  24  *     for the empty virtual function implementations for every
  25  *     nsIMutationObserver implementation)
  26  *  2. the performance of document's loop over observers benefits from
  27  *     the fact that more of the functions called are the same (which
  28  *     can reduce instruction cache misses and perhaps improve branch
  29  *     prediction)
  30  */
  31 class nsStubMutationObserver : public nsIMutationObserver {
  32  public:
  33   NS_DECL_NSIMUTATIONOBSERVER
  34 };
  35
  36 class MutationObserverWrapper;
  37
  38 /**
  39  * @brief Base class for MutationObservers that are used by multiple nodes.
  40  *
  41  * Mutation Observers are stored inside of a nsINode using a DoublyLinkedList,
  42  * restricting the number of nodes a mutation observer can be inserted to one.
  43  *
  44  * To allow a mutation observer to be used by several nodes, this class
  45  * provides a MutationObserverWrapper which implements the nsIMutationObserver
  46  * interface and forwards all method calls to this class. For each node this
  47  * mutation observer will be used for, a wrapper object is created.
  48  */
  49 class nsMultiMutationObserver : public nsIMutationObserver {
  50  public:
  51   /**
  52    * Adds the mutation observer to aNode by creating a MutationObserverWrapper
  53    * and inserting it into aNode.
  54    * Does nothing if there already is a mutation observer for aNode.
  55    */
  56   void AddMutationObserverToNode(nsINode* aNode);
  57
  58   /**
  59    * Removes the mutation observer from aNode.
  60    * Does nothing if there is no mutation observer for aNode.
  61    */
  62   void RemoveMutationObserverFromNode(nsINode* aNode);
  63
  64   /**
  65    * Returns true if there is already a mutation observer for aNode.
  66    */
  67   bool ContainsNode(const nsINode* aNode) const;
  68
  69  private:
  70   friend class MutationObserverWrapper;
  71   nsTHashMap<nsINode*, MutationObserverWrapper*> mWrapperForNode;
  72 };
  73
  74 /**
  75  * Convenience class that provides support for multiple nodes and has
  76  * default implementations for nsIMutationObserver.
  77  */
  78 class nsStubMultiMutationObserver : public nsMultiMutationObserver {
  79  public:
  80   NS_DECL_NSIMUTATIONOBSERVER
  81 };
  82
  83 #endif /* !defined(nsStubMutationObserver_h_) */