WeakRefEnumerator.cs source code in C# .NET

                        Code:
                         / DotNET / DotNET / 8.0 / untmp / WIN_WINDOWS / lh_tools_devdiv_wpf / Windows / wcp / Core / System / Windows / Media / Animation / WeakRefEnumerator.cs / 1 / WeakRefEnumerator.cs
                        
                        
                            //------------------------------------------------------------------------------ 
//  Microsoft Windows Client Platform
//  Copyright (c) Microsoft Corporation, 2003
//
//  File:       WeakRefEnumerator.cs 
//-----------------------------------------------------------------------------
 
using System; 
using System.Collections.Generic;
using System.Diagnostics; 

namespace System.Windows.Media.Animation
{
    ///  
    /// An enumerator for collections of weak references.
    ///  
    ///  
    /// The enumerator returns only live objects and removes dead
    /// references from the list as it walks. 
    /// 
    internal struct WeakRefEnumerator
    {
        #region Internal implementation 

        #region Construction 
 
        /// 
        /// Creates an enumerator for the given list. 
        /// 
        /// 
        /// The list to enumerate.
        ///  
        internal WeakRefEnumerator(List list)
        { 
            _list = list; 
            _readIndex = 0;
            _writeIndex = 0; 
            _current = default(T);

#if DEBUG
            _valid = false; 
#endif // DEBUG
        } 
 
        #endregion // Construction
 
        #region Properties

        /// 
        /// Gets the current element in the collection. 
        /// 
        ///  
        /// The current element in the collection. 
        /// 
        internal T Current 
        {
            get
            {
#if DEBUG 
                Debug.Assert(_valid);
#endif // DEBUG 
 
                return _current;
            } 
        }

        /// 
        /// Gets the index of the current element in the collection. 
        /// 
        ///  
        /// The index of the current element in the collection. 
        /// 
        internal int CurrentIndex 
        {
            get
            {
#if DEBUG 
                Debug.Assert(_valid);
#endif // DEBUG 
 
                return _writeIndex - 1;
            } 
        }

        #endregion // Properties
 
        #region Methods
 
        ///  
        /// This method must be called when the enumerator is no longer
        /// in use, if the last call to MoveNext returned true. The 
        /// enumerator is no longer valid after this call.
        /// 
        /// 
        /// When MoveNext returns false, the collection being enumerated is 
        /// left in a good, known state, so nothing additional needs to be
        /// done. However, before MoveNext returns false the collection is 
        /// in an intermediate state, so if the enumerator isn't advanced 
        /// all the way to the end then this method must be called to clean
        /// up the collection and make sure that it ends in a known state. 
        /// Calling this method in the case where MoveNext has returned
        /// false is OK. In that case, the method is a no-op.
        /// 
        internal void Dispose() 
        {
            // Remove only those elements that we've previously seen. 
            // This means removing the range between the read and write 
            // indices, as that's dead space in the collection.
            if (_readIndex != _writeIndex) 
            {
                _list.RemoveRange(_writeIndex, _readIndex - _writeIndex);
                _readIndex = _writeIndex = _list.Count;
            } 

            _current = default(T); 
 
#if DEBUG
            _valid = false; 
#endif // DEBUG
        }

        ///  
        /// Advances the enumerator to the next element of the collection.
        ///  
        ///  
        /// true if the enumerator was successfully advanced to the next
        /// element; false if the enumerator has passed the end of the 
        /// collection.
        /// 
        /// 
        /// Elements that have been GC'ed are removed from the list. 
        /// 
        internal bool MoveNext() 
        { 
            // Get a reference to the next element that has not yet been
            // garbage-collected 
            while (_readIndex < _list.Count)
            {
                WeakReference currentRef = _list[_readIndex];
                _current = (T)currentRef.Target; 
                if ( (object)_current != null)
                { 
                    // Found a live object. First compress the list, which 
                    // is necessary if we've previously seen GC'ed objects.
                    if (_writeIndex != _readIndex) 
                    {
                        _list[_writeIndex] = currentRef;
                    }
 
                    // Update internal state and return the found element
                    _readIndex++; 
                    _writeIndex++; 

#if DEBUG 
                    _valid = true;
#endif // DEBUG

                    return true; 
                }
                else 
                { 
                    // This object was garbage-collected, so keep looking
                    _readIndex++; 
                }
            }

            // If we get here we didn't have any more live elements in the 
            // collection, so we should return false. This is also a good
            // opportunity to clean up the list as necessary. 
            Dispose(); 

            return false; 
        }


        #endregion // Methods 

        #region Data 
 
        private List _list;
        private T                   _current; 
        private int                 _readIndex;
        private int                 _writeIndex;

#if DEBUG 
        private bool                _valid;
#endif // DEBUG 
 
        #endregion // Data
 
        #endregion // Internal implementation
    }
}

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