Csharp C#XmlSerializer输出控制新行的多个XML片段

发布于03月03日

我希望能够编写没有名称空间、没有XML前导的缩进XML片段，行结尾为\n，每个片段使用XmlSerializer，所有片段使用一个XmlWriter实例.我怎么能做到这一点？

XmlSerializer.Serialize()在序列化到通用输出流时生成缩进输出，但它使用"\n\r"作为行尾，我找不到如何配置它.

我可以序列化到XmlWriter，可以对其进行详细配置，但似乎只有在输出完整的单个文档而不是多个文档片段时，配置才起作用，因为XmlSerializer将抛出异常ConformanceLevel.Fragment:

无法在使用ConformanceLevel.Fragment创建的编写器上调用WriteStartDocument

而且，如果我调用XmlWriter.WriteWhitespace("");作为变通方法，缩进将被禁用. 具体来说，如果我像这样创建一个XmlWriter:

XmlWriter xw = XmlWriter.Create(System.Console.Out, new XmlWriterSettings()
{
    ConformanceLevel = ConformanceLevel.Fragment,
    NamespaceHandling = NamespaceHandling.Default,
    NewLineChars = "\n",
    Encoding = new UTF8Encoding(encoderShouldEmitUTF8Identifier: false), // supress BOM
    Indent = true,
    NewLineHandling = NewLineHandling.Replace,
    OmitXmlDeclaration = true,
    WriteEndDocumentOnClose = false,
    CloseOutput = false,
    CheckCharacters = false,
    NewLineOnAttributes = false,
});

MVE

https://dotnetfiddle.net/qGLIlL个它确实允许我序列化多个对象，而无需 for each 对象创建新的XmlWriter.但没有凹痕.

<flyingMonkey name="Koko"><limbs><limb name="leg" /><limb name="arm" /><limb name="tail" /><limb name="wing" /></limbs></flyingMonkey>

<flyingMonkey name="New Name"><limbs><limb name="leg" /><limb name="arm" /><limb name="tail" /><limb name="wing" /></limbs></flyingMonkey>

public class Program {
    public static void Main()
    {
        XmlWriter xw = XmlWriter.Create(System.Console.Out, new XmlWriterSettings()
        {
            ConformanceLevel = ConformanceLevel.Fragment,
            NamespaceHandling = NamespaceHandling.Default,
            NewLineChars = "\n",
            Encoding = new UTF8Encoding(encoderShouldEmitUTF8Identifier: false), // supress BOM
            Indent = true,
            NewLineHandling = NewLineHandling.Replace,
            OmitXmlDeclaration = true,
            WriteEndDocumentOnClose = false,
            CloseOutput = false,
            CheckCharacters = false,
            NewLineOnAttributes = false,
        });
        var noNamespace = new XmlSerializerNamespaces(new[] { XmlQualifiedName.Empty });

        // without this line I get an error:
        //   "无法在使用ConformanceLevel.Fragment创建的编写器上调用WriteStartDocument."
        xw.WriteWhitespace("");

        FlyingMonkey monkey = FlyingMonkey.Create();
        XmlSerializer ser = new XmlSerializer(typeof(FlyingMonkey), defaultNamespace: null);
        ser.Serialize(xw, monkey, noNamespace);
        xw.WriteWhitespace("\n\n");
        monkey.name = "New Name";
        ser.Serialize(xw, monkey, noNamespace);
    }
}

[System.Xml.Serialization.XmlTypeAttribute(TypeName = "flyingMonkey", Namespace=null)]
public class FlyingMonkey
{
    [System.Xml.Serialization.XmlAttributeAttribute()]
    public string name;

    public Limb[] limbs;

    public static FlyingMonkey Create() =>
        new FlyingMonkey()
        {
            name = "Koko",
            limbs = new Limb[]
            {
                new Limb() { name = "leg" }, new Limb() { name = "arm" },
                new Limb() { name = "tail" }, new Limb() { name = "wing" },
            }
        };
}

[System.Xml.Serialization.XmlTypeAttribute(TypeName = "limb", Namespace=null)]
public class Limb
{
    [System.Xml.Serialization.XmlAttributeAttribute()]
    public string name;
}

有几分管用:

XmlWriter xw = XmlWriter.Create(System.Console.Out, new XmlWriterSettings()
{
    ConformanceLevel = ConformanceLevel.Auto,
    NamespaceHandling = NamespaceHandling.Default,
    NewLineChars = "\n",
    Encoding = new UTF8Encoding(encoderShouldEmitUTF8Identifier: false), // supress BOM
    Indent = true,
    NewLineHandling = NewLineHandling.Replace,
    OmitXmlDeclaration = true,
    WriteEndDocumentOnClose = false,
    CloseOutput = false,
    CheckCharacters = false,
    NewLineOnAttributes = false,
});
var noNamespace = new XmlSerializerNamespaces(new[] { XmlQualifiedName.Empty });

// This is not needed anymore. If I invoke that, it will kill indentation for some reason.
// xw.WriteWhitespace("");

FlyingMonkey monkey = FlyingMonkey.Create();
XmlSerializer ser = new XmlSerializer(typeof(FlyingMonkey), defaultNamespace: null);
ser.Serialize(xw, monkey, noNamespace);
// xw.WriteWhitespace("\n\n");
// monkey.name = "New Name";
// ser.Serialize(xw, monkey, noNamespace); // this second serialization throws InvalidOperationException

它以正确的行尾打印，但不允许您将另一个对象写入同一个XmlWriter实例.

<flyingMonkey name="Koko">
  <limbs>
    <limb name="leg" />
    <limb name="arm" />
    <limb name="tail" />
    <limb name="wing" />
  </limbs>
</flyingMonkey>

我想要重用我的XmlWriter的单个实例，因为我需要编写多达XmlWriterk个元素，并且 for each 元素创建XmlWriter会增加大量开销

public static partial class XmlExtensions { static Encoding Utf8EncodingNoBom { get; } = new UTF8Encoding(encoderShouldEmitUTF8Identifier: false); public static void SerializeFragmentsToXml<T>(this IEnumerable<T> enumerable, Stream stream, XmlSerializer? serializer = null, XmlSerializerNamespaces? ns = null) { var newLine = "\n"; var newLineBytes = Utf8EncodingNoBom.GetBytes(newLine+newLine); var settings = new XmlWriterSettings() { NamespaceHandling = NamespaceHandling.Default, NewLineChars = newLine, Encoding = Utf8EncodingNoBom, // supress BOM Indent = true, NewLineHandling = NewLineHandling.Replace, OmitXmlDeclaration = true, WriteEndDocumentOnClose = false, CloseOutput = false, // Required to prevent the stream from being closed between items CheckCharacters = false, NewLineOnAttributes = false, }; serializer ??= new XmlSerializer(typeof(T)); ns ??= new XmlSerializerNamespaces(new[] { XmlQualifiedName.Empty }); bool first = true; foreach (var item in enumerable) { if (!first) stream.Write(newLineBytes); using (var xmlWriter = XmlWriter.Create(stream, settings)) serializer.Serialize(xmlWriter, item, ns); first = false; } } }

var items = new [] { "Koko", "POCO", "Loco" }.Select(n => FlyingMonkey.Create(n)); using var stream = new MemoryStream(); // Replace with some FileStream when serializing to disk var serializer = new XmlSerializer(typeof(FlyingMonkey), defaultNamespace: null); items.SerializeFragmentsToXml(stream, serializer : serializer);

public static partial class XmlExtensions { const string FirstCommentText = "first"; const string FirstComment = $""; const string SubsequentCommentText = "subsequent"; const string SubsequentComment = $""; static Encoding Utf8EncodingNoBom { get; } = new UTF8Encoding(encoderShouldEmitUTF8Identifier: false); public static void SerializeFragmentsToXml<T>(this IEnumerable<T> enumerable, Stream stream, XmlSerializer? serializer = null, XmlSerializerNamespaces? ns = null) { string newLine = "\n"; var settings = new XmlWriterSettings() { ConformanceLevel = ConformanceLevel.Fragment, NamespaceHandling = NamespaceHandling.Default, NewLineChars = newLine, Encoding = Utf8EncodingNoBom, // supress BOM Indent = true, NewLineHandling = NewLineHandling.Replace, OmitXmlDeclaration = true, WriteEndDocumentOnClose = false, CloseOutput = false, CheckCharacters = false, NewLineOnAttributes = false, }; serializer ??= new XmlSerializer(typeof(T)); ns ??= new XmlSerializerNamespaces(new[] { XmlQualifiedName.Empty }); using var innerTextWriter = new StreamWriter(stream, encoding : Utf8EncodingNoBom, leaveOpen : true) { NewLine = newLine }; using var textWriter = new FakeCommentRemovingTextWriter(innerTextWriter, new(FirstComment, ""), new(SubsequentComment, newLine)) { NewLine = newLine }; using var xmlWriter = XmlWriter.Create(textWriter, settings); bool first = true; foreach (var item in enumerable) { xmlWriter.WriteComment(first ? FirstCommentText : SubsequentCommentText); serializer.Serialize(xmlWriter, item, ns); // XmlWriter buffers its output, so Flush() is required to ensure that the fake comments are not split across calls to Write(). xmlWriter.Flush(); first = false; } } private class FakeCommentRemovingTextWriter : TextWriterDecorator { readonly KeyValuePair<string, string> [] replacements; public FakeCommentRemovingTextWriter(TextWriter baseWriter, params KeyValuePair<string, string> [] replacements) : base(baseWriter, true) => this.replacements = replacements; public override void Write(ReadOnlySpan<char> buffer) { foreach (var replacement in replacements) { int index; if ((index = StartsWithIgnoringWhitespace(buffer, replacement.Key)) >= 0) { if (index > 0) base.Write(buffer.Slice(0, index)); buffer = buffer.Slice(index).Slice(replacement.Key.Length); if (buffer.StartsWith(NewLine)) buffer = buffer.Slice(NewLine.Length); if (!string.IsNullOrEmpty(replacement.Value)) base.Write(replacement.Value); } } base.Write(buffer); } static int StartsWithIgnoringWhitespace(ReadOnlySpan<char> buffer, ReadOnlySpan<char> value) { for (int index = 0; index < buffer.Length; index++) { if (buffer.Slice(index).StartsWith(value)) return index; if (!XmlConvert.IsWhitespaceChar(buffer[index]) || index >= buffer.Length - value.Length) break; } return -1; } } } public class TextWriterDecorator : TextWriter { // Override the same methods that are overridden in https://github.com/dotnet/runtime/blob/main/src/libraries/System.Private.CoreLib/src/System/IO/StringWriter.cs. TextWriter? baseWriter; // null when disposed readonly bool disposeBase; readonly Encoding baseEncoding; public TextWriterDecorator(TextWriter baseWriter, bool disposeBase = true) => (this.baseWriter, this.disposeBase, this.baseEncoding) = (baseWriter ?? throw new ArgumentNullException(nameof(baseWriter)), disposeBase, baseWriter.Encoding); protected TextWriter BaseWriter => baseWriter == null ? throw new ObjectDisposedException(GetType().Name) : baseWriter; public override Encoding Encoding => baseEncoding; public override IFormatProvider FormatProvider => baseWriter?.FormatProvider ?? base.FormatProvider; [AllowNull] public override string NewLine { get => baseWriter?.NewLine ?? base.NewLine; set { if (baseWriter != null) baseWriter.NewLine = value; base.NewLine = value; } } public override void Flush() => BaseWriter.Flush(); public sealed override void Close() => Dispose(true); public override void Write(char value) => BaseWriter.Write(value); public sealed override void Write(char[] buffer, int index, int count) => this.Write(buffer.AsSpan(index, count)); public override void Write(ReadOnlySpan<char> buffer) => BaseWriter.Write(buffer); public sealed override void Write(string? value) => Write(value.AsSpan()); public override Task WriteAsync(char value) => BaseWriter.WriteAsync(value); public sealed override Task WriteAsync(string? value) => WriteAsync(value.AsMemory()); public sealed override Task WriteAsync(char[] buffer, int index, int count) => WriteAsync(buffer.AsMemory(index, count)); public override Task WriteAsync(ReadOnlyMemory<char> buffer, CancellationToken cancellationToken = default) => BaseWriter.WriteAsync(buffer, cancellationToken); //public virtual Task WriteAsync(StringBuilder? value, CancellationToken cancellationToken = default) - no need to override public override Task WriteLineAsync(char value) => BaseWriter.WriteLineAsync(value); public sealed override Task WriteLineAsync(string? value) => WriteLineAsync(value.AsMemory()); public override Task WriteLineAsync(StringBuilder? value, CancellationToken cancellationToken = default) => BaseWriter.WriteLineAsync(value, cancellationToken); public sealed override Task WriteLineAsync(char[] buffer, int index, int count) => WriteLineAsync(buffer.AsMemory(index, count)); public override Task WriteLineAsync(ReadOnlyMemory<char> buffer, CancellationToken cancellationToken = default) => BaseWriter.WriteLineAsync(buffer, cancellationToken); public override Task FlushAsync() => BaseWriter.FlushAsync(); public override Task FlushAsync(CancellationToken cancellationToken) => BaseWriter.FlushAsync(cancellationToken); protected override void Dispose(bool disposing) { try { if (disposing) { if (Interlocked.Exchange(ref this.baseWriter, null) is {} writer) if (disposeBase) writer.Dispose(); else writer.Flush(); } } finally { base.Dispose(disposing); } } public override async ValueTask DisposeAsync() { try { if (Interlocked.Exchange(ref this.baseWriter, null) is {} writer) if (disposeBase) await writer.DisposeAsync().ConfigureAwait(false); else await writer.FlushAsync().ConfigureAwait(false); } finally { await base.DisposeAsync().ConfigureAwait(false); } } public override string ToString() => string.Format("{0}: {1}", GetType().Name, baseWriter?.ToString() ?? "disposed"); }

<flyingMonkey name="Koko"> <limbs> <limb name="leg" /> <limb name="arm" /> <limb name="tail" /> <limb name="wing" /> </limbs> </flyingMonkey> <flyingMonkey name="POCO"> <limbs> <limb name="leg" /> <limb name="arm" /> <limb name="tail" /> <limb name="wing" /> </limbs> </flyingMonkey> <flyingMonkey name="Loco"> <limbs> <limb name="leg" /> <limb name="arm" /> <limb name="tail" /> <limb name="wing" /> </limbs> </flyingMonkey>

Csharp C#XmlSerializer输出控制新行的多个XML片段

MVE

有几分管用:

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