如何在C#生成的XML中为Envelope添加s:前缀？

需求目标 #

需要生成如下XML结构：

<s:Envelope xmlns:s="http://schemas.xmlsoap.org/soap/envelope/" 
            xmlns:a="http://www.w3.org/2005/08/addressing" 
            xmlns:fse="http://www.sist.puglia.it/Schemas/PDD_SIST/SCATEL/FSE/" 
            xmlns:u="http://docs.oasisopen.org/wss/2004/01/oasis-200401-wss-wssecurity-utility-1.0.xsd">
</s:Envelope>

之前的错误尝试及问题 #

第一次尝试代码 #

XNamespace myns = "s";

XDocument oXml = new XDocument(new XDeclaration("1.0", "UTF-8", ""));

XElement oRoot = new XElement("Envelope",
    new XAttribute(XNamespace.Xmlns + "s", "http://schemas.xmlsoap.org/soap/envelope/"),
    new XAttribute(XNamespace.Xmlns + "a", "http://www.w3.org/2005/08/addressing"),
    new XAttribute(XNamespace.Xmlns + "fse", "http://www.sist.puglia.it/Schemas/PDD_SIST/SCATEL/FSE/"),
    new XAttribute(XNamespace.Xmlns + "u", "http://docs.oasisopen.org/wss/2004/01/oasis-200401-wss-wssecurity-utility-1.0.xsd")
);

oXml.Add(oRoot);

生成结果缺少s:前缀：

<Envelope xmlns:s="http://schemas.xmlsoap.org/soap/envelope/" 
          xmlns:a="http://www.w3.org/2005/08/addressing" 
          xmlns:fse="http://www.sist.puglia.it/Schemas/PDD_SIST/SCATEL/FSE/" 
          xmlns:u="http://docs.oasisopen.org/wss/2004/01/oasis-200401-wss-wssecurity-utility-1.0.xsd" />

第二次尝试代码 #

XNamespace myns = "s";

XElement oRoot = new XElement(myns + "Envelope",
    new XAttribute(XNamespace.Xmlns + "s", "http://schemas.xmlsoap.org/soap/envelope/"),
    new XAttribute(XNamespace.Xmlns + "a", "http://www.w3.org/2005/08/addressing"),
    new XAttribute(XNamespace.Xmlns + "fse", "http://www.sist.puglia.it/Schemas/PDD_SIST/SCATEL/FSE/"),
    new XAttribute(XNamespace.Xmlns + "u", "http://docs.oasisopen.org/wss/2004/01/oasis-200401-wss-wssecurity-utility-1.0.xsd")
);

生成结果多出了xmlns="s"属性：

<Envelope xmlns:s="http://schemas.xmlsoap.org/soap/envelope/" 
          xmlns:a="http://www.w3.org/2005/08/addressing" 
          xmlns:fse="http://www.sist.puglia.it/Schemas/PDD_SIST/SCATEL/FSE/" 
          xmlns:u="http://docs.oasisopen.org/wss/2004/01/oasis-200401-wss-wssecurity-utility-1.0.xsd" 
          xmlns="s" />

错误原因 #

核心问题是XNamespace的赋值错误：你把XNamespace myns设成了前缀s，但实际上XNamespace需要绑定的是命名空间的URI，而不是前缀。前缀s是通过Xmlns属性来关联到对应URI的。

正确解决方案 #

修正XNamespace的定义，将其设置为SOAP信封的命名空间URI，然后创建XElement时使用该命名空间+元素名，同时保留原有的Xmlns属性定义：

// 正确定义命名空间为SOAP信封的URI
XNamespace sNs = "http://schemas.xmlsoap.org/soap/envelope/";

XDocument oXml = new XDocument(new XDeclaration("1.0", "UTF-8", ""));

XElement oRoot = new XElement(sNs + "Envelope",
    // 绑定前缀s到对应的命名空间URI
    new XAttribute(XNamespace.Xmlns + "s", sNs),
    new XAttribute(XNamespace.Xmlns + "a", "http://www.w3.org/2005/08/addressing"),
    new XAttribute(XNamespace.Xmlns + "fse", "http://www.sist.puglia.it/Schemas/PDD_SIST/SCATEL/FSE/"),
    new XAttribute(XNamespace.Xmlns + "u", "http://docs.oasisopen.org/wss/2004/01/oasis-200401-wss-wssecurity-utility-1.0.xsd")
);

oXml.Add(oRoot);

生成的正确结果 #

<s:Envelope xmlns:s="http://schemas.xmlsoap.org/soap/envelope/" 
            xmlns:a="http://www.w3.org/2005/08/addressing" 
            xmlns:fse="http://www.sist.puglia.it/Schemas/PDD_SIST/SCATEL/FSE/" 
            xmlns:u="http://docs.oasisopen.org/wss/2004/01/oasis-200401-wss-wssecurity-utility-1.0.xsd" />

内容的提问来源于stack exchange，提问作者Modest