Code:
/ 4.0 / 4.0 / untmp / DEVDIV_TFS / Dev10 / Releases / RTMRel / wpf / src / Base / MS / Internal / ObservableCollectionDefaultValueFactory.cs / 1305600 / ObservableCollectionDefaultValueFactory.cs
//---------------------------------------------------------------------------- // //// Copyright (C) Microsoft Corporation. All rights reserved. // // // Description: DefaultvalueFactory for ObservableCollection // // History: // 2009/24/07 : [....] - Created. // //--------------------------------------------------------------------------- using MS.Internal.WindowsBase; using System; using System.Diagnostics; using System.Windows; using System.Collections.ObjectModel; // ObservableCollection using System.Collections.Specialized; // NotifyCollectionChangedEventHandler namespace MS.Internal { //// ObservableCollectionDefaultValueFactory is a DefaultValueFactory implementation which will // promote the default value to a local value if the collection is modified. // [FriendAccessAllowed] // built into Base, used by Framework internal class ObservableCollectionDefaultValueFactory: DefaultValueFactory { internal ObservableCollectionDefaultValueFactory() { _default = new ObservableCollection (); } /// /// This is used for Sealed objects. ObservableCollections are inherently mutable, so they shouldn't /// be used with sealed objects. The PropertyDescriptor calls this, so we'll just return the same empty collection. /// internal override object DefaultValue { get { return _default; } } ////// internal override object CreateDefaultValue(DependencyObject owner, DependencyProperty property) { Debug.Assert(owner != null && property != null, "It is the caller responsibility to ensure that owner and property are non-null."); var result = new ObservableCollection(); // Wire up a ObservableCollectionDefaultPromoter to observe the default value we // just created and automatically promote it to local if it is modified. // NOTE: We do not holding a reference to this because it should have the same lifetime as // the collection. It will not be immediately GC'ed because it hooks the collections change event. new ObservableCollectionDefaultPromoter(owner, property, result); return result; } /// /// The ObservableCollectionDefaultPromoter observes the mutable defaults we hand out /// for changed events. If the default is ever modified this class will /// promote it to a local value by writing it to the local store and /// clear the cached default value so we will generate a new default /// the next time the property system is asked for one. /// private class ObservableCollectionDefaultPromoter { internal ObservableCollectionDefaultPromoter(DependencyObject owner, DependencyProperty property, ObservableCollectioncollection) { Debug.Assert(owner != null && property != null, "Caller is responsible for ensuring that owner and property are non-null."); Debug.Assert(property.GetMetadata(owner.DependencyObjectType).UsingDefaultValueFactory, "How did we end up observing a mutable if we were not registered for the factory pattern?"); // We hang on to the property and owner so we can write the default // value back to the local store if it changes. See also // OnDefaultValueChanged. _owner = owner; _property = property; _collection = collection; _collection.CollectionChanged += OnDefaultValueChanged; } internal void OnDefaultValueChanged(object sender, NotifyCollectionChangedEventArgs e) { PropertyMetadata metadata = _property.GetMetadata(_owner.DependencyObjectType); // Remove this value from the DefaultValue cache so we stop // handing it out as the default value now that it has changed. metadata.ClearCachedDefaultValue(_owner, _property); // If someone else hasn't already written a local value, // promote the default value to local. if (_owner.ReadLocalValue(_property) == DependencyProperty.UnsetValue) { // Read-only properties must be set using the Key if (_property.ReadOnly) { _owner.SetValue(_property.DependencyPropertyKey, _collection); } else { _owner.SetValue(_property, _collection); } } // Unhook the change handler because we're finsihed promoting _collection.CollectionChanged -= OnDefaultValueChanged; } private readonly DependencyObject _owner; private readonly DependencyProperty _property; private readonly ObservableCollection _collection; } private ObservableCollection _default; } } // File provided for Reference Use Only by Microsoft Corporation (c) 2007. // Copyright (c) Microsoft Corporation. All rights reserved.
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