Code:
/ DotNET / DotNET / 8.0 / untmp / WIN_WINDOWS / lh_tools_devdiv_wpf / Windows / wcp / TrustUi / MS / Internal / documents / Application / WriteableOnDemandStream.cs / 1 / WriteableOnDemandStream.cs
//------------------------------------------------------------------------------ //// Copyright (C) Microsoft Corporation. All rights reserved. // //// This class acts as a type of proxy; it is responsible for forwarding all // stream requests to the active stream. Unlike a proxy it is also controls // which stream is active. Initially the active stream is the stream provided // at construction, at the time of the first write operation the active stream // is replaced with one provided by a delegate. // // History: // 07/04/2005: [....]: Initial implementation. // 08/28/2005: [....]: Adjusted spacing and style to match team better //----------------------------------------------------------------------------- using System; using System.IO; using System.Windows.TrustUI; namespace MS.Internal.Documents.Application { ////// This class acts as a type of proxy; it is responsible for forwarding all /// stream requests to the active stream. Unlike a proxy it is also /// controls which stream is active. Initially the active stream is the /// stream provided on construction, at the time of the first write /// operation the active stream is replaced with one provided by a delegate. /// ////// As this class only proxies the abstract methods of Stream, if we are /// proxing a stream that has overriden other virutal methods behavioral /// inconsistencies may occur. This could be solved by forwarding all /// calls. For internal use it is not currently needed. /// internal sealed class WriteableOnDemandStream : Stream { #region Constructors //------------------------------------------------------------------------- // Constructors //------------------------------------------------------------------------- ////// Constructs the class with readingStream as the active Stream. /// ////// The read only Stream. /// FileMode that will be use to create write /// stream. /// FileAccess that will be use to create write /// stream. /// Delegate used to create a /// write stream on first write operation. internal WriteableOnDemandStream( Stream readingStream, FileMode mode, FileAccess access, GetWriteableInstance writeableStreamFactory) { if (readingStream == null) { throw new ArgumentNullException("readingStream"); } if (writeableStreamFactory == null) { throw new ArgumentNullException("writeableStreamFactory"); } _active = readingStream; _mode = mode; _access = access; _writeableStreamFactory = writeableStreamFactory; _wantedWrite = ((_access == FileAccess.ReadWrite) || (_access == FileAccess.Write)); } #endregion Constructors #region Stream Overrides //-------------------------------------------------------------------------- // Stream Overrides //------------------------------------------------------------------------- // Due to sub-nesting of pure proxies vs. decorating ones code structure // is simplier in this case by grouping Methods & Properies. #region Pure Proxies for Stream //-------------------------------------------------------------------------- // This region of code simply follows the proxy patern and only forwards // the calls to the active stream. //-------------------------------------------------------------------------- /// /// public override bool CanRead { get { return _active.CanRead; } } ////// /// public override bool CanSeek { get { return _active.CanSeek; } } ////// /// public override void Flush() { Trace.SafeWriteIf( _isActiveWriteable, Trace.Packaging, "Flush is being called on read-only stream."); if (_isActiveWriteable) { _active.Flush(); } } ////// /// public override long Length { get { return _active.Length; } } ////// /// public override long Position { get { return _active.Position; } set { _active.Position = value; } } ////// /// public override int Read(byte[] buffer, int offset, int count) { return _active.Read(buffer, offset, count); } ////// /// public override long Seek(long offset, SeekOrigin origin) { return _active.Seek(offset, origin); } #endregion Pure Proxies for Stream #region Decorating Proxies for Stream //------------------------------------------------------------------------- // This region of code follows the decorator patern, the added behavior // is the replacement of the active stream with one that is writeable // on the first write operation. //-------------------------------------------------------------------------- ////// /// public override bool CanWrite { get { // asking if we can write is not a write operation, // however, as the active type had to implement this // abstract property thier implementation is the one // we should prefer, when we are writable, until then // it's more efficent to assume if the user asked for // write it will be supported if (_isActiveWriteable) { return _active.CanWrite; } else { return _wantedWrite; } } } ////// /// public override void SetLength(long value) { EnsureWritable(); _active.SetLength(value); } ////// /// public override void Write(byte[] buffer, int offset, int count) { EnsureWritable(); _active.Write(buffer, offset, count); } #endregion Decorating Proxies for Stream #endregion Stream Overrides #region Internal Delegates //------------------------------------------------------------------------- // Internal Delegates //------------------------------------------------------------------------- ////// /// The delegate is use as a factory to return writable copy of the /// stream we were originally given. /// /// The FileMode desired. /// The FileAccess desired. ///A writeable Stream. public delegate Stream GetWriteableInstance( FileMode mode, FileAccess access); #endregion Internal Delegates #region Protected Methods - Stream Overrides //------------------------------------------------------------------------- // Protected Methods - Stream Overrides //-------------------------------------------------------------------------- ////// Ensure we do not aquire new resources. /// /// Indicates if we are disposing. protected override void Dispose(bool disposing) { try { if (disposing) { if (_isActiveWriteable && _active.CanWrite) { _active.Flush(); // we do not want to dispose of _active // first we are merely a proxy; and being done with // us is not the same as being done with the PackagePart // it supprots, the Package which created _active // is calls dispose } _isActiveWriteable = true; } } finally { base.Dispose(disposing); } } #endregion Protected Methods - Stream Overrides #region Private Methods //------------------------------------------------------------------------- // Private Methods //-------------------------------------------------------------------------- ////// Ensures either the active stream is our writeable stream or uses the /// factory delegate to get one and assign it as the active stream. /// ////// private void EnsureWritable() { if (!_wantedWrite) { throw new NotSupportedException( SR.Get(SRID.PackagingWriteNotSupported)); } if (!_isActiveWriteable) { Stream writer = _writeableStreamFactory(_mode, _access); if (writer == null) { throw new IOException( SR.Get(SRID.PackagingWriteableDelegateGaveNullStream)); } if (writer.Equals(this)) { throw new IOException( SR.Get(SRID.PackagingCircularReference)); } writer.Position = _active.Position; _active = writer; _isActiveWriteable = true; } } #endregion Private Methods #region Private Fields //-------------------------------------------------------------------------- // Private Fields //------------------------------------------------------------------------- /// /// The delegate we were given to have a writeable stream created. /// private GetWriteableInstance _writeableStreamFactory; ////// The stream we should be currently using. /// private Stream _active; ////// Whether the active stream is writeable. /// private bool _isActiveWriteable; ////// The caller's desired FileMode provided on construction. /// private FileMode _mode; ////// The caller's desired FileAccess provided on construction. /// private FileAccess _access; ////// Calculated using FileAccess, it determines if writing was indicated. /// private bool _wantedWrite; #endregion Private Methods } } // File provided for Reference Use Only by Microsoft Corporation (c) 2007. // Copyright (c) Microsoft Corporation. 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