XmlElementCollection.cs source code in C# .NET

                        Code:
                         / 4.0 / 4.0 / untmp / DEVDIV_TFS / Dev10 / Releases / RTMRel / wpf / src / Framework / MS / Internal / Annotations / XmlElementCollection.cs / 1305600 / XmlElementCollection.cs
                        
                        
                            //---------------------------------------------------------------------------- 
//
// 
//    Copyright (C) 2003 by Microsoft Corporation.  All rights reserved.
//  
//
// 
// Description: Subclass of ObservableCollection which also registers for 
//              change notifications from the XmlElements it contains.  It fires
//              CollectionChanged event with action==Reset for any item that 
//              changed.  This is sufficient to let owner objects know an item
//              has changed.
//
// History: 
//  03/10/2005 : rruiz - created
// 
//--------------------------------------------------------------------------- 

using System; 
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Collections.Specialized;
using System.ComponentModel; 
using System.Diagnostics;
using System.Windows; 
using System.Windows.Data; 
using System.Xml;
using MS.Internal; 

namespace MS.Internal.Annotations
{
    ///  
    /// 
    internal sealed class XmlElementCollection : ObservableCollection 
    { 
        //-----------------------------------------------------
        // 
        //  Constructors
        //
        //-----------------------------------------------------
 
        #region Constructors
 
        ///  
        /// Initializes a new instance of XmlElementCollection that is empty and has default initial capacity.
        ///  
        public XmlElementCollection() : base()
        {
            _xmlDocsRefCounts = new Dictionary();
        } 

        #endregion Constructors 
 
        //------------------------------------------------------
        // 
        //  Public Events
        //
        //-----------------------------------------------------
 
        //------------------------------------------------------
        // 
        //  Protected Methods 
        //
        //------------------------------------------------------ 

        #region Protected Methods

        ///  
        /// called by base class Collection<T> when the list is being cleared;
        /// unregisters from all items 
        ///  
        protected override void ClearItems()
        { 
            foreach (XmlElement item in this)
            {
                UnregisterForElement(item);
            } 

            base.ClearItems(); 
        } 

        ///  
        /// called by base class Collection<T> when an item is removed from list;
        /// unregisters on item being removed
        /// 
        protected override void RemoveItem(int index) 
        {
            XmlElement removedItem = this[index]; 
 
            UnregisterForElement(removedItem);
 
            base.RemoveItem(index);
        }

        ///  
        /// called by base class Collection<T> when an item is added to list;
        /// registers on new item 
        ///  
        protected override void InsertItem(int index, XmlElement item)
        { 
            if (item != null && this.Contains(item))
            {
                throw new ArgumentException(SR.Get(SRID.XmlNodeAlreadyOwned, "change", "change"), "item");
            } 

            base.InsertItem(index, item); 
 
            RegisterForElement(item);
        } 

        /// 
        /// called by base class Collection<T> when an item is added to list;
        /// unregisters on previous item and registers for new item 
        /// 
        protected override void SetItem(int index, XmlElement item) 
        { 
            if (item != null && this.Contains(item))
            { 
                throw new ArgumentException(SR.Get(SRID.XmlNodeAlreadyOwned, "change", "change"), "item");
            }

            XmlElement originalItem = this[index]; 

            UnregisterForElement(originalItem); 
 
            Items[index] = item;    // directly set Collection inner Items collection
            OnCollectionReset(); 

            RegisterForElement(item);
        }
 
        #endregion Protected Methods
 
 
        //-----------------------------------------------------
        // 
        //  Private Methods
        //
        //------------------------------------------------------
 
        #region Private Methods
 
        ///  
        ///     Unregister for change notifications for this element.
        ///     We decrease the reference count and unregister if the count 
        ///     has reached zero.
        /// 
        /// the element to unregister for
        private void UnregisterForElement(XmlElement element) 
        {
            // Nulls may exist in the collection in which case we don't need to unregister 
            if (element == null) 
                return;
 
            Invariant.Assert(_xmlDocsRefCounts.ContainsKey(element.OwnerDocument), "Not registered on XmlElement");

            // Decrease the reference count
            _xmlDocsRefCounts[element.OwnerDocument]--; 

            // If the reference count is at zero, we can unregister for notifications 
            // from the document and clear out its entry in the hashtable. 
            if (_xmlDocsRefCounts[element.OwnerDocument] == 0)
            { 
                element.OwnerDocument.NodeChanged -= OnNodeChanged;
                element.OwnerDocument.NodeInserted -= OnNodeChanged;
                element.OwnerDocument.NodeRemoved -= OnNodeChanged;
                _xmlDocsRefCounts.Remove(element.OwnerDocument); 
            }
        } 
 
        /// 
        ///     Register for change notifications for this element.  In 
        ///     reality we regiser on the OwnerDocument, so we keep a count
        ///     of all the elements from a particular docuemnt we are listening
        ///     for.  If that ref count gets to zero we unregister from the
        ///     document. 
        /// 
        /// the element to register for 
        private void RegisterForElement(XmlElement element) 
        {
            // Nulls may exist in the collection in which case we don't need to register 
            if (element == null)
                return;

            if (!_xmlDocsRefCounts.ContainsKey(element.OwnerDocument)) 
            {
                // If we aren't register on this document yet, register 
                // and initialize the reference count to 1. 
                _xmlDocsRefCounts[element.OwnerDocument] = 1;
                XmlNodeChangedEventHandler handler = new XmlNodeChangedEventHandler(OnNodeChanged); 
                element.OwnerDocument.NodeChanged += handler;
                element.OwnerDocument.NodeInserted += handler;
                element.OwnerDocument.NodeRemoved += handler;
            } 
            else
            { 
                // Increase the reference count 
                _xmlDocsRefCounts[element.OwnerDocument]++;
            } 
        }

        /// 
        ///     We register for node changes on the documents that own the contents 
        ///     of this Resource.  Its the only way to know if the contents have
        ///     changed. 
        ///  
        /// document whose node has changed
        /// args describing the kind of change and specifying the node that changed 
        private void OnNodeChanged(object sender, XmlNodeChangedEventArgs args)
        {
            XmlAttribute attr = null;
            XmlElement element = null; 

            // We should only be getting notifications from documents we have registered on 
            Invariant.Assert(_xmlDocsRefCounts.ContainsKey(sender as XmlDocument), "Not expecting a notification from this sender"); 

            // The node that changed may not be a content but could be a part of a content 
            // (such as an attribute node).  Therefore we must walk up from the node until
            // we either a) get to the root or b) find a content we contain.  In the case of
            // (a) we do nothing.  In the case of (b) we must fire a change notification
            // for this Resource. 
            XmlNode current = args.Node;
            while (current != null) 
            { 
                element = current as XmlElement;
                if (element != null && this.Contains(element)) 
                {
                    OnCollectionReset();
                    break;
                } 

                // Get the parent of the current node 
                attr = current as XmlAttribute; 
                if (attr != null)
                { 
                    // ParentNode isn't implemented for XmlAttributes, we must
                    // use its OwnerElement to continue our walk up the node tree.
                    current = attr.OwnerElement;
                } 
                else
                { 
                    current = current.ParentNode; 
                }
            } 
        }

        private void OnCollectionReset()
        { 
            OnCollectionChanged(new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Reset));
        } 
 
        #endregion Private Methods
 
        //-----------------------------------------------------
        //
        //  Private Fields
        // 
        //-----------------------------------------------------
 
        #region Private Fields 

        Dictionary  _xmlDocsRefCounts; 

        #endregion Private Fields
    }
} 

// File provided for Reference Use Only by Microsoft Corporation (c) 2007.
// Copyright (c) Microsoft Corporation. All rights reserved.
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XmlElementCollection.cs source code in C# .NET

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