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/ 4.0 / 4.0 / untmp / DEVDIV_TFS / Dev10 / Releases / RTMRel / wpf / src / Core / CSharp / System / Windows / Media / Animation / WeakRefEnumerator.cs / 1305600 / 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(Listlist) { _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 The /// enumerator is no longer valid after this call.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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