FreezableDefaultValueFactory.cs source code in C# .NET

                        Code:
                         / 4.0 / 4.0 / untmp / DEVDIV_TFS / Dev10 / Releases / RTMRel / wpf / src / Base / MS / Internal / FreezableDefaultValueFactory.cs / 1305600 / FreezableDefaultValueFactory.cs
                        
                        
                            //---------------------------------------------------------------------------- 
//
// 
//    Copyright (C) Microsoft Corporation.  All rights reserved.
//  
//
// Description: DefaultvalueFactory for Freezables 
// 
// History:
//  2005/11/08 : [....] - Created from PresentationCore's old 
//                          MutableDefaultPropertyMetadata
//
//---------------------------------------------------------------------------
 
using MS.Internal.WindowsBase;
using System; 
using System.Diagnostics; 
using System.Windows;
 
namespace MS.Internal
{
    // 
    // FreezableDefaultValueFactory is a DefaultValueFactory implementation which 
    // is inserted by the property system for any DP registered with a default
    // value of type Freezable. The userï¿½s given default value is frozen and 
    // used as a template to create unfrozen copies on a per DP per DO basis. If 
    // the default value is modified it is automatically promoted from default to
    // local. 
    // 
    [FriendAccessAllowed] // built into Base, used by Core + Framework
    internal class FreezableDefaultValueFactory : DefaultValueFactory
    { 

        ///  
        ///     Stores a frozen copy of defaultValue 
        /// 
        internal FreezableDefaultValueFactory(Freezable defaultValue) 
        {
            Debug.Assert(defaultValue != null,
                "Null can not be made mutable.  Do not use FreezableDefaultValueFactory.");
            Debug.Assert(defaultValue.CanFreeze, 
                "The defaultValue prototype must be freezable.");
 
            _defaultValuePrototype = defaultValue.GetAsFrozen(); 
        }
 
        /// 
        ///     Returns our frozen sentinel
        /// 
        internal override object DefaultValue 
        {
            get 
            { 
                Debug.Assert(_defaultValuePrototype.IsFrozen);
 
                return _defaultValuePrototype;
            }
        }
 
        /// 
        ///     If the DO is frozen, we'll return our frozen sentinel. Otherwise we'll make 
        ///     an unfrozen copy. 
        /// 
        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.");
 
            Freezable result = _defaultValuePrototype;
            Freezable ownerFreezable = owner as Freezable; 
 
            // If the owner is frozen, just return the frozen prototype.
            if (ownerFreezable != null && ownerFreezable.IsFrozen) 
            {
                return result;
            }
 
            result = _defaultValuePrototype.Clone();
 
            // Wire up a FreezableDefaultPromoter to observe the default value we 
            // just created and automatically promote it to local if it is modified.
            FreezableDefaultPromoter promoter = new FreezableDefaultPromoter(owner, property); 
            promoter.SetFreezableDefaultValue(result);
            result.Changed += promoter.OnDefaultValueChanged;

            return result; 
        }
 
        // This is the prototype that CreateDefaultValue copies to create the 
        // mutable default value for this property.  See also the ctor.
        private readonly Freezable _defaultValuePrototype; 

        /// 
        ///     The FreezableDefaultPromoter 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 FreezableDefaultPromoter 
        {
            internal FreezableDefaultPromoter(DependencyObject owner, DependencyProperty property)
            {
                Debug.Assert(owner != null && property != null, 
                    "Caller is responsible for ensuring that owner and property are non-null.");
                Debug.Assert(!(owner is Freezable) || !((Freezable)owner).IsFrozen, 
                    "We should not be observing mutables on a frozen owner."); 
                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; 
            } 

            internal void OnDefaultValueChanged(object sender, EventArgs e) 
            {
                Debug.Assert(_mutableDefaultValue != null,
                    "Promoter's creator should have called SetFreezableDefaultValue.");
 
                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); 

                // Since Changed is raised when the user freezes the default
                // value, we need to check before removing our handler.
                // (If the value is frozen, it will remove it's own handlers.) 
                if (!_mutableDefaultValue.IsFrozen)
                { 
                    _mutableDefaultValue.Changed -= OnDefaultValueChanged; 
                }
 
                // If someone else hasn't already written a local local value,
                // promote the default value to local.
                if (_owner.ReadLocalValue(_property) == DependencyProperty.UnsetValue)
                { 
                    _owner.SetMutableDefaultValue(_property, _mutableDefaultValue);
                } 
            } 

            private readonly DependencyObject _owner; 
            private readonly DependencyProperty _property;

            #region DefaultValue
 
            // The creator of a FreezableDefaultValuePromoter should call this method
            // so that we can verify that the changed sender is the mutable default 
            // value we handed out. 
            internal void SetFreezableDefaultValue(Freezable mutableDefaultValue)
            { 
                _mutableDefaultValue = mutableDefaultValue;
            }

 
            private Freezable _mutableDefaultValue;
 
            #endregion DefaultValue 

        } 
    }
}

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

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