c# deserialize to an object from a file - out of memory

Question

I posted and answered a question about how to serialize a rather large (~150 meg) object to a file without getting an out-of-memory exception. That now works. Now I need to deserialize the file back into an object.

I am getting an out of memory error at the buffer allocation part of this code. I'm thinking there is a way I can get the streams arranged so I don't have to read into a temporary buffer first, but need help.

public static object Deserialize(Type objType, FileInfo xmlDocFile)
{
    object returnValue = null;
    if (xmlDocFile != null && objType != null && xmlDocFile.Exists)
    {
        DataContractSerializer formatter = new DataContractSerializer(objType);
        ASCIIEncoding encoder = new ASCIIEncoding();
        byte[] buffer = null;
        using (FileStream textFile = new FileStream(xmlDocFile.FullName, FileMode.Open))
        {
            buffer = new byte[textFile.Length];   // Out-of-memory thrown here
            textFile.Read(buffer, 0, buffer.Length);
        }
        XmlDictionaryReader reader = XmlDictionaryReader.CreateTextReader(buffer, new XmlDictionaryReaderQuotas());
        returnValue = formatter.ReadObject(reader, true);
    }
    return returnValue;
}

The code I use to serialize the object is this

public static void Serialize(object obj, FileInfo destination)
{
    if (null != obj)
    {
        using (TextWriter writer = new StreamWriter(destination.FullName, false))
        {
            XmlTextWriter xmlWriter = null;
            try
            {
                xmlWriter = new XmlTextWriter(writer);
                DataContractSerializer formatter = new DataContractSerializer(obj.GetType());
                formatter.WriteObject(xmlWriter, obj);
            }
            finally
            {
                if (xmlWriter != null)
                {
                    xmlWriter.Flush();
                    xmlWriter.Close();
                }
            }
        }
    }
}

Answer 1

The solution I came up with (which is very close to the one by Petrov) is:

public static object Deserialize(Type objType, FileInfo xmlDocFile)
{
    object returnValue = null;            
    if (xmlDocFile != null && objType != null && xmlDocFile.Exists)
    {
        DataContractSerializer formatter = new DataContractSerializer(objType);
        using (FileStream fs = File.Open(xmlDocFile.FullName, FileMode.Open, FileAccess.Read, FileShare.ReadWrite))
        {
            using (BufferedStream bs = new BufferedStream(fs))
            {
                XmlDictionaryReader reader = XmlDictionaryReader.CreateTextReader(bs, Encoding.UTF8, new XmlDictionaryReaderQuotas(), null);
                returnValue = formatter.ReadObject(reader, true);
            }
        }
    }

    return returnValue;
}

Answer 2

No need to read the file into memory. Pass the stream into the DataContractSerializer.

public static object Deserialize(Type objType, FileInfo xmlDocFile)
{
    object returnValue = null;
    if (xmlDocFile != null && objType != null && xmlDocFile.Exists)
    {
        DataContractSerializer formatter = new DataContractSerializer(objType);

        using (FileStream textFile = new FileStream(xmlDocFile.FullName, FileMode.Open))
        {
            returnValue = formatter.ReadObject(textFile);
        }
    }
    return returnValue;
}