DecoderFallbackWithFailureFlag.cs source code in C# .NET

                        Code:
                         / 4.0 / 4.0 / untmp / DEVDIV_TFS / Dev10 / Releases / RTMRel / wpf / src / Shared / MS / Internal / DecoderFallbackWithFailureFlag.cs / 1305600 / DecoderFallbackWithFailureFlag.cs
                        
                        
                            //---------------------------------------------------------------------------- 
//
// Copyright (c) Microsoft Corporation.  All rights reserved.
//
// 
// Description: DecoderFallbackWithFailureFlag is used when the developer wants Encoding.GetChars() method to fail
//              without throwing an exception when decoding cannot be performed. 
//  Usage pattern is: 
//      DecoderFallbackWithFailureFlag fallback = new DecoderFallbackWithFailureFlag();
//      Encoding e = Encoding.GetEncoding(codePage, EncoderFallback.ExceptionFallback, fallback); 
//      e.GetChars(bytesToDecode);
//      if (fallback.HasFailed)
//      {
//          // Perform fallback and reset the failure flag. 
//          fallback.HasFailed = false;
//      } 
// 
// History:
//  05/03/2005 : mleonov - Created 
//
//---------------------------------------------------------------------------

using System.Text; 

namespace MS.Internal 
{ 
    /// 
    /// This class is similar to the standard DecoderExceptionFallback class, 
    /// except that for performance reasons it sets a Boolean failure flag
    /// instead of throwing exception.
    /// 
    internal class DecoderFallbackWithFailureFlag : DecoderFallback 
    {
        public DecoderFallbackWithFailureFlag() 
        { } 

        public override DecoderFallbackBuffer CreateFallbackBuffer() 
        {
            return new FallbackBuffer(this);
        }
 
        /// 
        /// The maximum number of characters this instance can return. 
        ///  
        public override int MaxCharCount
        { 
            get
            {
                return 0;
            } 
        }
 
        ///  
        /// Returns whether decoding failed.
        ///  
        public bool HasFailed
        {
            get
            { 
                return _hasFailed;
            } 
            set 
            {
                _hasFailed = value; 
            }
        }

        private bool _hasFailed; // false by default 

        ///  
        /// A special implementation of DecoderFallbackBuffer that sets the failure flag 
        /// in the parent DecoderFallbackWithFailureFlag class.
        ///  
        private class FallbackBuffer : DecoderFallbackBuffer
        {
            public FallbackBuffer(DecoderFallbackWithFailureFlag parent)
            { 
                _parent = parent;
            } 
 
            /// 
            /// Indicates whether a substitute string can be emitted if an input byte sequence cannot be decoded. 
            /// Parameters specify an input byte sequence, and the index position of a byte in the input.
            /// 
            /// An input array of bytes.
            /// The index position of a byte in bytesUnknown. 
            /// true if a string exists that can be inserted in the output
            /// instead of decoding the byte specified in bytesUnknown; 
            /// false if the input byte should be ignored. 
            public override bool Fallback(byte[] bytesUnknown, int index)
            { 
                _parent.HasFailed = true;
                return false;
            }
 
            /// 
            /// Retrieves the next character in the fallback buffer. 
            ///  
            /// The next Unicode character in the fallback buffer.
            public override char GetNextChar() 
            {
                return (char)0;
            }
 
            /// 
            /// Prepares the GetNextChar method to retrieve the preceding character in the fallback buffer. 
            ///  
            /// true if the MovePrevious operation was successful; otherwise, false.
            public override bool MovePrevious() 
            {
                return false;
            }
 
            /// 
            /// Gets the number of characters in this instance of DecoderFallbackBuffer that remain to be processed. 
            ///  
            public override int Remaining
            { 
                get
                {
                    return 0;
                } 
            }
 
            private DecoderFallbackWithFailureFlag _parent; 
        }
    } 
}

// File provided for Reference Use Only by Microsoft Corporation (c) 2007.
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DecoderFallbackWithFailureFlag.cs source code in C# .NET

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