ResourceReferenceExpression.cs source code in C# .NET

                        Code:
                         / 4.0 / 4.0 / untmp / DEVDIV_TFS / Dev10 / Releases / RTMRel / wpf / src / Framework / System / Windows / ResourceReferenceExpression.cs / 1586769 / ResourceReferenceExpression.cs
                        
                        
                            //---------------------------------------------------------------------------- 
//
// File: ResourceReferenceExpression.cs
//
// Description: 
//   Expression to evaluate a ResourceReference.
// 
// Copyright (C) 2003 by Microsoft Corporation.  All rights reserved. 
//
//--------------------------------------------------------------------------- 

using System;
using System.ComponentModel;
using System.Diagnostics; 
using System.Windows.Markup;
using MS.Internal; 
 
namespace System.Windows
{ 
    /// 
    ///     Expression to evaluate a ResourceReference
    /// 
    [TypeConverter(typeof(ResourceReferenceExpressionConverter))] 
    internal class ResourceReferenceExpression : Expression
    { 
        ///  
        ///     Constructor for ResourceReferenceExpression
        ///  
        /// 
        ///     Name of the resource being referenced
        /// 
        public ResourceReferenceExpression(object resourceKey) 
        {
            _resourceKey = resourceKey; 
        } 

        ///  
        ///     List of sources of the ResourceReferenceExpression
        /// 
        /// Sources list
        internal override DependencySource[] GetSources() 
        {
            return null; 
        } 

        ///  
        ///     Called to evaluate the ResourceReferenceExpression value
        /// 
        /// DependencyObject being queried
        /// Property being queried 
        /// Computed value. Unset if unavailable.
        internal override object GetValue(DependencyObject d, DependencyProperty dp) 
        { 
            if (d == null)
            { 
                throw new ArgumentNullException("d");
            }
            if (dp == null)
            { 
                throw new ArgumentNullException("dp");
            } 
 
            // If the cached value is valid then return it
            if (ReadInternalState(InternalState.HasCachedResourceValue) == true) 
                return _cachedResourceValue;

            object source;
            return GetRawValue(d, out source, dp); 
        }
 
 
        // Clone a copy of this expression (this is used by Freezable.Copy)
        internal override Expression Copy( DependencyObject targetObject, DependencyProperty targetDP ) 
        {
            return new ResourceReferenceExpression( ResourceKey );
        }
 

        ///  
        ///     Called to evaluate the ResourceReferenceExpression value 
        /// 
        /// DependencyObject being queried 
        /// Source object that the resource is found on
        /// DependencyProperty
        /// Computed value. Unset if unavailable.
        ///  
        /// This routine has been separated from the above GetValue call because it is
        /// invoked by the ResourceReferenceExpressionConverter during serialization. 
        ///  
        internal object GetRawValue(DependencyObject d, out object source, DependencyProperty dp)
        { 
            // Find the mentor node to invoke FindResource on. For example
            //  
        ///     Allows ResourceReferenceExpression to store set values
        ///  
        /// DependencyObject being set 
        /// Property being set
        /// Value being set 
        /// true if ResourceReferenceExpression handled storing of the value
        internal override bool SetValue(DependencyObject d, DependencyProperty dp, object value)
        {
            return false; 
        }
 
        ///  
        ///     Notification that the ResourceReferenceExpression has been set as a property's value
        ///  
        /// DependencyObject being set
        /// Property being set
        internal override void OnAttach(DependencyObject d, DependencyProperty dp)
        { 
            _targetObject = d;
            _targetProperty = dp; 
 
            FrameworkObject fo = new FrameworkObject(_targetObject);
 
            fo.HasResourceReference = true;

            if (!fo.IsValid)
            { 
                // Listen for the InheritanceContextChanged event on the target node,
                // so that if this context hierarchy changes we can re-evaluate this expression. 
                _targetObject.InheritanceContextChanged += new EventHandler(InvalidateExpressionValue); 
            }
        } 

        /// 
        ///     Notification that the ResourceReferenceExpression has been removed as a property's value
        ///  
        /// DependencyObject being cleared
        /// Property being cleared 
        internal override void OnDetach(DependencyObject d, DependencyProperty dp) 
        {
            // Invalidate all the caches 
            InvalidateMentorCache();

            if (!(_targetObject is FrameworkElement) && !(_targetObject is FrameworkContentElement))
            { 
                // Stop listening for the InheritanceContextChanged event on the target node
                _targetObject.InheritanceContextChanged -= new EventHandler(InvalidateExpressionValue); 
            } 

            _targetObject = null; 
            _targetProperty = null;
            // RemoveChangedHandler will have already been called via InvalidateMentorCache().
            _weakContainerRRE = null;
        } 

        ///  
        ///     Key used to lookup the resource 
        /// 
        public object ResourceKey 
        {
            get { return _resourceKey; }
        }
 
        /// 
        /// This method is called when the cached value of the resource has 
        /// been invalidated.  E.g. after a new Resources property is set somewhere 
        /// in the ancestory.
        ///  
        private void InvalidateCacheValue()
        {
            object resource = _cachedResourceValue;
 
            // If the old value was a DeferredResourceReference, it should be
            // removed from its Dictionary's list to avoid a leak (bug 1624666). 
            DeferredResourceReference deferredResourceReference = _cachedResourceValue as DeferredResourceReference; 
            if (deferredResourceReference != null)
            { 
                if (deferredResourceReference.IsInflated)
                {
                    // use the inflated value for the Freezable test below
                    resource = deferredResourceReference.Value; 
                }
                else 
                { 
                    // stop listening for the Inflated event
                    if (ReadInternalState(InternalState.IsListeningForInflated)) 
                    {
                        deferredResourceReference.RemoveInflatedListener(this);
                        WriteInternalState(InternalState.IsListeningForInflated, false);
                    } 
                }
 
                deferredResourceReference.RemoveFromDictionary(); 
            }
 
            StopListeningForFreezableChanges(resource);

            _cachedResourceValue = null;
            WriteInternalState(InternalState.HasCachedResourceValue, false); 
        }
 
        ///  
        ///     This method is called to invalidate all the cached values held in
        ///     this expression. This is called under the following 3 scenarios 
        ///     1. InheritanceContext changes
        ///     2. Logical tree changes
        ///     3. ResourceDictionary changes
        ///     This call is more pervasive than the InvalidateCacheValue method 
        /// 
        private void InvalidateMentorCache() 
        { 
            if (ReadInternalState(InternalState.IsMentorCacheValid) == true)
            { 
                if (_mentorCache != null)
                {
                    if (_mentorCache != _targetObject)
                    { 
                        FrameworkElement mentorFE;
                        FrameworkContentElement mentorFCE; 
                        Helper.DowncastToFEorFCE(_mentorCache, out mentorFE, out mentorFCE, true); 

                        // Your mentor is about to change, make sure you detach handlers for 
                        // the events that you were listening on the old mentor
                        if (mentorFE != null)
                        {
                            mentorFE.ResourcesChanged -= new EventHandler(InvalidateExpressionValue); 
                        }
                        else 
                        { 
                            mentorFCE.ResourcesChanged -= new EventHandler(InvalidateExpressionValue);
                        } 
                    }

                    // Drop the mentor cache
                    _mentorCache = null; 
                }
 
                // Mark the cache invalid 
                WriteInternalState(InternalState.IsMentorCacheValid, false);
            } 

            // Invalidate the cached value of the expression
            InvalidateCacheValue();
        } 

        ///  
        ///     This event handler is called to invalidate the cached value held in 
        ///     this expression. This is called under the following 3 scenarios
        ///     1. InheritanceContext changes 
        ///     2. Logical tree changes
        ///     3. ResourceDictionary changes
        /// 
        internal void InvalidateExpressionValue(object sender, EventArgs e) 
        {
            // VS has a scenario where a TreeWalk invalidates all reference expressions on a DependencyObject. 
            // If there is a dependency between RRE's, 
            // invalidating one RRE could cause _targetObject to be null on the other RRE. Hence this check.
            if (_targetObject == null) 
            {
                return;
            }
 
            ResourcesChangedEventArgs args = e as ResourcesChangedEventArgs;
            if (args != null) 
            { 
                ResourcesChangeInfo info = args.Info;
                if (!info.IsTreeChange) 
                {
                    // This will happen when
                    // 1. Theme changes
                    // 2. Entire ResourceDictionary in the ancestry changes 
                    // 3. Single entry in a ResourceDictionary in the ancestry is changed
                    // In all of the above cases it is sufficient to re-evaluate the cache 
                    // value alone. The mentor relation ships stay the same. 
                    InvalidateCacheValue();
                } 
                else
                {
                    // This is the case of a logical tree change and hence we need to
                    // re-evaluate both the mentor and the cached value. 
                    InvalidateMentorCache();
                } 
            } 
            else
            { 
                // There is no information provided by the EventArgs. Hence we
                // pessimistically invalidate both the mentor and the cached value.
                // This code path will execute when the InheritanceContext changes.
                InvalidateMentorCache(); 
            }
 
            InvalidateTargetProperty(sender, e); 
        }
 
        private void InvalidateTargetProperty(object sender, EventArgs e)
        {
            _targetObject.InvalidateProperty(_targetProperty);
        } 

        private void InvalidateTargetSubProperty(object sender, EventArgs e) 
        { 
            _targetObject.NotifySubPropertyChange(_targetProperty);
        } 

        private void ListenForFreezableChanges(object resource)
        {
            if (!ReadInternalState(InternalState.IsListeningForFreezableChanges)) 
            {
                // If this value is an unfrozen Freezable object, we need 
                //  to listen to its changed event in order to properly update 
                //  the cache.
                Freezable resourceAsFreezable = resource as Freezable; 
                if( resourceAsFreezable != null && !resourceAsFreezable.IsFrozen )
                {
                    if (_weakContainerRRE == null)
                    { 
                        _weakContainerRRE = new ResourceReferenceExpressionWeakContainer(this);
                    } 
 
                    // Hook up the event to the weak container to prevent memory leaks (Bug436021)
                    _weakContainerRRE.AddChangedHandler(resourceAsFreezable); 
                    WriteInternalState(InternalState.IsListeningForFreezableChanges, true);
                }
            }
        } 

        private void StopListeningForFreezableChanges(object resource) 
        { 
            if (ReadInternalState(InternalState.IsListeningForFreezableChanges))
            { 
                // If the old value was an unfrozen Freezable object, we need
                //  to stop listening to its changed event.  If the old value wasn't
                //  frozen (hence we attached an listener) but has been frozen
                //  since then, the change handler we had attached was already 
                //  discarded during the freeze so we don't care here.
                Freezable resourceAsFreezable = resource as Freezable; 
                if (resourceAsFreezable != null && _weakContainerRRE != null) 
                {
                    if (!resourceAsFreezable.IsFrozen) 
                    {
                        _weakContainerRRE.RemoveChangedHandler();
                    }
                    else 
                    {
                        // Resource is frozen so we can discard the weak reference. 
                        _weakContainerRRE = null; 
                    }
                } 

                // It is possible that a freezable was unfrozen during the call to ListForFreezableChanges
                // but was frozen before the call to StopListeningForFreezableChanges
                WriteInternalState(InternalState.IsListeningForFreezableChanges, false); 
            }
        } 
 
        // when a deferred resource reference is inflated, the value may need extra
        // work 
        internal void OnDeferredResourceInflated(DeferredResourceReference deferredResourceReference)
        {
            if (ReadInternalState(InternalState.IsListeningForInflated))
            { 
                // once the value is inflated, stop listening for the event
                deferredResourceReference.RemoveInflatedListener(this); 
                WriteInternalState(InternalState.IsListeningForInflated, false); 
            }
 
            ListenForFreezableChanges(deferredResourceReference.Value);
        }

        // Extracts the required flag and returns 
        // bool to indicate if it is set or unset
        private bool ReadInternalState(InternalState reqFlag) 
        { 
            return (_state & reqFlag) != 0;
        } 

        // Sets or Unsets the required flag based on
        // the bool argument
        private void WriteInternalState(InternalState reqFlag, bool set) 
        {
            if (set) 
            { 
                _state |= reqFlag;
            } 
            else
            {
                _state &= (~reqFlag);
            } 
        }
 
        private object _resourceKey; // Name of the resource being referenced by this expression 

        // Cached value and a dirty bit.  See GetValue. 
        private object _cachedResourceValue;

        // Used to find the value for this expression when it is set on a non-FE/FCE.
        // The mentor is the FE/FCE that the FindResource method is invoked on. 
        private DependencyObject _mentorCache;
 
        // Used by the change listener to fire invalidation. 
        private DependencyObject _targetObject;
        private DependencyProperty _targetProperty; 

        // Bit Fields used to store boolean flags
        private InternalState _state = InternalState.Default;  // this is a byte (see def'n)
 
        private ResourceReferenceExpressionWeakContainer _weakContainerRRE = null;
 
        ///  
        /// This enum represents the internal state of the RRE.
        /// Additional bools should be coalesced into this enum. 
        /// 
        [Flags]
        private enum InternalState : byte
        { 
            Default                       = 0x00,
            HasCachedResourceValue        = 0x01, 
            IsMentorCacheValid            = 0x02, 
            DisableThrowOnResourceFailure = 0x04,
            IsListeningForFreezableChanges= 0x08, 
            IsListeningForInflated        = 0x10,
        }

        #region ResourceReferenceExpressionWeakContainer 

        ///  
        /// ResourceReferenceExpressionWeakContainer handles the Freezable.Changed event 
        /// without holding a strong reference to ResourceReferenceExpression.
        ///  
        private class ResourceReferenceExpressionWeakContainer : WeakReference
        {
            public ResourceReferenceExpressionWeakContainer(ResourceReferenceExpression target)
                : base(target) {} 

            private void InvalidateTargetSubProperty(object sender, EventArgs args) 
            { 
                ResourceReferenceExpression expression = (ResourceReferenceExpression)Target;
                if (expression != null) 
                {
                    expression.InvalidateTargetSubProperty(sender, args);
                }
                else 
                {
                    RemoveChangedHandler(); 
                } 
            }
 
            public void AddChangedHandler(Freezable resource)
            {
                // If _resource already exists, unhook the event handler.
                if (_resource != null) 
                {
                    RemoveChangedHandler(); 
                } 

                _resource = resource; 

                Debug.Assert(!_resource.IsFrozen);
                _resource.Changed += new EventHandler(this.InvalidateTargetSubProperty);
            } 

            public void RemoveChangedHandler() 
            { 
                Debug.Assert(!_resource.IsFrozen);
                _resource.Changed -= new EventHandler(this.InvalidateTargetSubProperty); 
                _resource = null;
            }

            private Freezable _resource; 
        }
        #endregion 
    } 

    ///  
    ///     These EventArgs are used to pass additional
    ///     information during a ResourcesChanged event
    /// 
    internal class ResourcesChangedEventArgs : EventArgs 
    {
        internal ResourcesChangedEventArgs(ResourcesChangeInfo info) 
        { 
            _info = info;
        } 

        internal ResourcesChangeInfo Info
        {
            get { return _info; } 
        }
 
        private ResourcesChangeInfo _info; 
    }
} 


// File provided for Reference Use Only by Microsoft Corporation (c) 2007.
// Copyright (c) Microsoft Corporation. All rights reserved.
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