如果您的 XML 文件太大而无法一次加载到内存中，您可以使用 XmlReader 流式传输文件并一次仅加载一小部分。此外，对于包含非常大的 Base64 编码二进制数据的<TestResultImage> 元素，您可以使用XmlReader.ReadElementContentAsBase64(Byte[], Int32, Int32) 以增量方式读取数据块并将它们复制到一些Stream 中。
下面的代码展示了如何做到这一点：
//https://stackoverflow.com/questions/49159697/deserializing-json-child-object-values-into-parent-object-using-jsonconvert-dese
public class MeanVarianceTestResultsData
{
public int ResultsID { get; set; }
public DateTime DateExecuted { get; set; }
public string UserExecuted { get; set; }
public string CorrectedMean { get; set; }
public string CorrectedVariance { get; set; }
public bool TestPassed { get; set; }
public string TestResultImageFile { get; set; }
public Stream TestResultImage { get; set; }
}
public static class MeanVarianceTestResultsDataExtensions
{
public static List<MeanVarianceTestResultsData> ReadResultListFrom(XmlReader reader, Func<MeanVarianceTestResultsData, Stream> openStream, Func<Stream, Stream> closeStream)
{
return reader.ReadSubtrees("TestResult").Select(r => ReadResultFrom(r, openStream, closeStream)).ToList();
}
public static MeanVarianceTestResultsData ReadResultFrom(XmlReader reader, Func<MeanVarianceTestResultsData, Stream> openStream, Func<Stream, Stream> closeStream)
{
if (reader == null || openStream == null)
throw new ArgumentNullException();
reader.MoveToContent();
var result = new MeanVarianceTestResultsData();
var isEmpty = reader.IsEmptyElement;
// Read the root
reader.Read();
if (isEmpty)
return result;
while (!reader.EOF)
{
if (reader.NodeType == XmlNodeType.EndElement)
{
reader.Read();
break;
}
else if (reader.NodeType != XmlNodeType.Element)
// Comment, text, CDATA, etc.
reader.Skip();
else if (reader.Name == "ResultsID")
result.ResultsID = reader.ReadElementContentAsInt();
else if (reader.Name == "DateExecuted")
result.DateExecuted = reader.ReadElementContentAsDateTime();
else if (reader.Name == "UserExecuted")
result.UserExecuted = reader.ReadElementContentAsString();
else if (reader.Name == "CorrectedMean")
result.CorrectedMean = reader.ReadElementContentAsString();
else if (reader.Name == "TestPassed")
result.TestPassed = reader.ReadElementContentAsBoolean();
else if (reader.Name == "TestResultImage")
result.TestResultImage = reader.ReadElementContentAsStream(() => openStream(result), closeStream);
else
reader.Skip();
}
return result;
}
}
public static class XmlReaderExtensions
{
public static Stream ReadElementContentAsStream(this XmlReader reader, Func<Stream> openStream, Func<Stream, Stream> closeStream)
{
if (reader == null || openStream == null)
throw new ArgumentNullException();
Stream stream = null;
try
{
stream = openStream();
byte[] buffer = new byte[4096];
int readBytes = 0;
while ((readBytes = reader.ReadElementContentAsBase64(buffer, 0, buffer.Length)) > 0)
{
stream.Write(buffer, 0, readBytes);
}
}
finally
{
if (closeStream != null && stream != null)
stream = closeStream(stream);
}
return stream;
}
public static IEnumerable<XmlReader> ReadSubtrees(this XmlReader reader, string name)
{
while (reader.ReadToFollowing(name))
{
using (var subReader = reader.ReadSubtree())
yield return subReader;
}
}
}
然后，您可以按如下方式使用它将每个TestResultImage 图像读入MemoryStream：
List<MeanVarianceTestResultsData> results;
using (var reader = XmlReader.Create(fileName))
{
results = MeanVarianceTestResultsDataExtensions.ReadResultListFrom(reader, m => new MemoryStream(), s => { s.Position = 0; return s; });
}
这将通过完全跳过图像的中间 Base64 字符串表示来节省大量内存 - 但它仍然会为每个 MemoryStream 使用大量内存。或者，您可以将图像流式传输到一些临时文件中以供以后使用，例如通过执行以下操作：
List<MeanVarianceTestResultsData> results;
using (var reader = XmlReader.Create(fileName))
{
results = MeanVarianceTestResultsDataExtensions.ReadResultListFrom(
reader,
m => { m.TestResultImageFile = Path.GetTempFileName(); return File.Open(m.TestResultImageFile, FileMode.Create); },
s => { s.Dispose(); return null; });
}
在这种情况下，每个流在图像写入后被释放，文件名存储在MeanVarianceTestResultsData 中。 （当然，如果您打算在反序列化后立即处理流，则可以让流保持打开状态。）
示例fiddle。