DependentList.cs source code in C# .NET

                        Code:
                         / DotNET / DotNET / 8.0 / untmp / WIN_WINDOWS / lh_tools_devdiv_wpf / Windows / wcp / Base / System / Windows / DependentList.cs / 1 / DependentList.cs
                        
                        
                            using System; 
using MS.Utility;
using MS.Internal;

namespace System.Windows 
{
    // 
    // The list of Dependents that depend on a Source[ID] 
    //
    // Steps are taken to guard against list corruption due to re-entrancy when 
    // the Invalidation callbacks call Add / Remove.   But multi-treaded
    // access is not expected and so locks are not used.
    //
    internal class DependentList: MS.Utility.FrugalObjectList 
    {
        static int _skipper=0; 
 
        public void Add(DependencyObject d, DependencyProperty dp, Expression expr)
        { 
            // don't clean up every time.  This will midigate the O(N) nature of Add().
            // Which would cause building a list to have O(N^2).  yuck!
            // Clean the list less often the longer it gets.
            if(0 == ++_skipper%(1+ (base.Count/4))) 
                CleanUpDeadWeakReferences(true);
 
            Dependent dep = new Dependent(d, dp, expr); 
            base.Add(dep);
        } 

        public void Remove(DependencyObject d, DependencyProperty dp, Expression expr)
        {
            Dependent dep = new Dependent(d, dp, expr); 
            base.Remove(dep);
        } 
 
        public bool IsEmpty
        { 
            get
            {
                if(0 == base.Count)
                    return true; 

                CleanUpDeadWeakReferences(false); 
                return 0 == base.Count; 
            }
        } 

        public void InvalidateDependents(DependencyObject source, DependencyPropertyChangedEventArgs sourceArgs)
        {
            // Take a snapshot of the list to protect against re-entrancy via Add / Remove. 
            Dependent[] snapList = base.ToArray();
 
            for(int i=0; i= 0; i--) 
            {
                if(!snapList[i].IsValid()) 
                { 
                    base.RemoveAt(i);
                } 
                else
                {
                    if(!doAll)
                        return; 
                }
            } 
        } 
    }
 
    internal struct Dependent
    {
        private DependencyProperty _DP;
        private WeakReference _wrDO; 
        private WeakReference _wrEX;
 
        public bool IsValid() 
        {
            // Expression is never null (could Assert that but throw is fine) 
            if(!_wrEX.IsAlive)
                return false;

            // It is OK to be null but if it isn't, then the target mustn't be dead. 
            if(null != _wrDO && !_wrDO.IsAlive)
                return false; 
 
            return true;
        } 

        public Dependent(DependencyObject o, DependencyProperty p, Expression e)
        {
            _wrEX = (null == e) ? null : new WeakReference(e); 
            _DP = p;
            _wrDO = (null == o) ? null : new WeakReference(o); 
        } 

        public DependencyObject DO 
        {
            get
            {
                if(null == _wrDO) 
                    return null;
                else 
                    return (DependencyObject)_wrDO.Target; 
            }
        } 

        public DependencyProperty DP
        {
            get { return _DP; } 
        }
 
        public Expression Expr 
        {
            get 
            {
                if(null == _wrEX)
                    return null;
                else 
                    return (Expression)_wrEX.Target;
            } 
        } 

        override public bool Equals(object o) 
        {
            if(! (o is Dependent))
                return false;
 
            Dependent d = (Dependent)o;
 
            // Not equal to Dead values. 
            // This is assuming that at least one of the compared items is live.
            // This assumtion comes from knowing that Equal is used by FrugalList.Remove() 
            // and if you look at DependentList.Remove()'s arguments, it can only
            // be passed strong references.
            // Therefore: Items being removed (thus compared here) will not be dead.
            if(!IsValid() || !d.IsValid()) 
                return false;
 
            if(_wrEX.Target != d._wrEX.Target) 
                return false;
 
            if(_DP != d._DP)
                return false;

            // if they are both non-null then the Targets must match. 
            if(null != _wrDO && null != d._wrDO)
            { 
                if(_wrDO.Target != d._wrDO.Target) 
                    return false;
            } 
            // but only one is non-null then they are not equal
            else if(null != _wrDO || null != d._wrDO)
                return false;
 
            return true;
        } 
 
        public static bool operator== (Dependent first, Dependent second)
        { 
            return first.Equals(second);
        }

        public static bool operator!= (Dependent first, Dependent second) 
        {
            return !(first.Equals(second)); 
        } 

        // We don't expect to need this function. [Required when overriding Equals()] 
        // Write a good HashCode anyway (if not a fast one)
        override public int GetHashCode()
        {
            int hashCode; 
            Expression ex = (Expression)_wrEX.Target;
            hashCode = (null == ex) ? 0 : ex.GetHashCode(); 
 
            if(null != _wrDO)
            { 
                DependencyObject DO = (DependencyObject)_wrDO.Target;
                hashCode += (null == DO) ? 0 : DO.GetHashCode();
            }
 
            hashCode += (null == _DP) ? 0 : _DP.GetHashCode();
            return hashCode; 
        } 
    }
} 


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

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