ObjectViewListener.cs source code in C# .NET

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                         / 4.0 / 4.0 / untmp / DEVDIV_TFS / Dev10 / Releases / RTMRel / ndp / fx / src / DataEntity / System / Data / Objects / ObjectViewListener.cs / 1305376 / ObjectViewListener.cs
                        
                        
                            //---------------------------------------------------------------------- 
// 
//      Copyright (c) Microsoft Corporation.  All rights reserved.
// 
// 
// @owner       [....]
// @backupOwner [....] 
//--------------------------------------------------------------------- 
using System;
using System.Collections; 
using System.Collections.Generic;
using System.ComponentModel;
using System.Data.Objects.DataClasses;
using System.Diagnostics; 

// Dev notes -1 
// why we need this class: in order to keep the view alive, we have to listen to evens from entities and 
// also EntityCollection/ObjectStateManager they exists in. listening to event will prevent the view to be
// disposed, hence GC'ed due to having a strong reference; and to avoid this situation we have to introduce 
// a new layer which will have a weakreference to view (1-so it can go out of scope, 2- this layer will listen to
// the events and notify the view - by calling its APIS-  for any change that happens)

// Dev notes -2 
// following statement is valid on current existing CLR:
// lets say Customer is an Entity, Array[Customer] is not Array[Entity]; it is not supported 
// to do the work around we have to use a non-Generic interface/class so we can pass the view 
// to ObjectViewListener safely (IObjectView)
 
namespace System.Data.Objects
{
    internal sealed class ObjectViewListener
    { 
        private WeakReference _viewWeak;
        private object _dataSource; 
        private IList _list; 

        internal ObjectViewListener(IObjectView view, IList list, object dataSource) 
        {
            _viewWeak = new WeakReference(view);
            _dataSource = dataSource;
            _list = list; 

            RegisterCollectionEvents(); 
            RegisterEntityEvents(); 
        }
 
        private void CleanUpListener()
        {
            UnregisterCollectionEvents();
            UnregisterEntityEvents(); 
        }
 
        private void RegisterCollectionEvents() 
        {
            ObjectStateManager cache = _dataSource as ObjectStateManager; 
            if (cache != null)
            {
                cache.EntityDeleted += CollectionChanged;
            } 
            else if (null != _dataSource)
            { 
                ((RelatedEnd)_dataSource).AssociationChangedForObjectView += CollectionChanged; 
            }
        } 

        private void UnregisterCollectionEvents()
        {
            ObjectStateManager cache = _dataSource as ObjectStateManager; 
            if (cache != null)
            { 
                cache.EntityDeleted -= CollectionChanged; 
            }
            else if (null != _dataSource) 
            {
                ((RelatedEnd)_dataSource).AssociationChangedForObjectView -= CollectionChanged;
            }
        } 

        internal void RegisterEntityEvents(object entity) 
        { 
            Debug.Assert(entity != null, "Entity should not be null");
            INotifyPropertyChanged propChanged = entity as INotifyPropertyChanged; 
            if (propChanged != null)
            {
                propChanged.PropertyChanged += EntityPropertyChanged;
            } 
        }
 
        private void RegisterEntityEvents() 
        {
            if (null != _list) 
            {
                foreach (object entityObject in _list)
                {
                    INotifyPropertyChanged propChanged = entityObject as INotifyPropertyChanged; 
                    if (propChanged != null)
                    { 
                        propChanged.PropertyChanged += EntityPropertyChanged; 
                    }
                } 
            }
        }

        internal void UnregisterEntityEvents(object entity) 
        {
            Debug.Assert(entity != null, "entity should not be null"); 
            INotifyPropertyChanged propChanged = entity as INotifyPropertyChanged; 
            if (propChanged != null)
            { 
                propChanged.PropertyChanged -= EntityPropertyChanged;
            }
        }
 
        private void UnregisterEntityEvents()
        { 
            if (null != _list) 
            {
                foreach (object entityObject in _list) 
                {
                    INotifyPropertyChanged propChanged = entityObject as INotifyPropertyChanged;
                    if (propChanged != null)
                    { 
                        propChanged.PropertyChanged -= EntityPropertyChanged;
                    } 
                } 
            }
        } 

        private void EntityPropertyChanged(object sender, PropertyChangedEventArgs e)
        {
            IObjectView view = (IObjectView)_viewWeak.Target; 
            if (view != null)
            { 
                view.EntityPropertyChanged(sender, e); 
            }
            else 
            {
                CleanUpListener();
            }
        } 

        private void CollectionChanged(object sender, CollectionChangeEventArgs e) 
        { 
            IObjectView view = (IObjectView)_viewWeak.Target;
            if (view != null) 
            {
                view.CollectionChanged(sender, e);
            }
            else 
            {
                CleanUpListener(); 
            } 
        }
    } 
}

// File provided for Reference Use Only by Microsoft Corporation (c) 2007.
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ObjectViewListener.cs source code in C# .NET

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