.NET 8升级后CustomXml Part无法通过FeedData更新问题排查

将项目从.NET Framework 4.8升级到.NET 8后，原本更新Word文档CustomXml Part的代码报entries cannot be opened multiple times in update mode错误，调整流的读取方式后，新代码调用FeedData却未生效，返回的仍是旧的CustomXml内容。

旧代码（.NET Framework 4.8下可用） #

public byte[] RenewCustomXmlPart(byte[] content, string customXml)
{
    using (m_log.CreateScope())
    {
        MemoryStream mem = CreateMemoryStream(content);

        if (mem == null)
        {
            return null;
        }

        using (WordprocessingDocument mergedDocument = WordprocessingDocument.Open(mem, true))
        {
            foreach (CustomXmlPart item in mergedDocument.MainDocumentPart.CustomXmlParts)
            {
                XDocument doc = XDocument.Load(new XmlTextReader(item.GetStream()));
                if (doc.Document == null)
                {
                    throw new ArgumentNullException(nameof(doc.Document));
                }
                if (doc.Document.Root == null)
                {
                    throw new ArgumentNullException(nameof(doc.Document.Root));
                }
                XNamespace xn = doc.Document.Root.GetDefaultNamespace();

                if (xn.NamespaceName == GlobalDefinitions.CustomXmlBausteinNamespace)
                {
                    byte[] a = Encoding.UTF8.GetBytes(customXml);
                    MemoryStream m = new MemoryStream(a);
                    item.FeedData(m);
                }
            }
            mem.Flush();
            return mem.ToArray();
        }
    }
}

新代码（调整后失效） #

public byte[] RenewCustomXmlPart(byte[] content, string customXml)
{
    using (m_log.CreateScope())
    {
        using MemoryStream mem = CreateMemoryStream(content);
        if (mem == null)
        {
            return null;
        }

        using WordprocessingDocument mergedDocument = WordprocessingDocument.Open(mem, true);
        foreach (CustomXmlPart item in mergedDocument.MainDocumentPart.CustomXmlParts)
        {
            using (Stream stream = item.GetStream(FileMode.Open, FileAccess.Read))
            {
                XDocument doc = XDocument.Load(new XmlTextReader(stream));
                if (doc.Document == null)
                {
                    throw new ArgumentNullException(nameof(doc.Document));
                }
                if (doc.Document.Root == null)
                {
                    throw new ArgumentNullException(nameof(doc.Document.Root));
                }

                XNamespace xn = doc.Document.Root.GetDefaultNamespace();
                if (xn.NamespaceName != GlobalDefinitions.CustomXmlBausteinNamespace)
                {
                    continue;
                }
            }

            byte[] newCustomXmlBytes = Encoding.UTF8.GetBytes(customXml);
            using MemoryStream m = new(newCustomXmlBytes);
            item.FeedData(m);
        }

        mem.Flush();
        return mem.ToArray();
    }
}

错误原因分析 #

1. 集合枚举与修改冲突：.NET 8版本的OpenXML SDK对集合枚举的校验更严格，直接遍历mergedDocument.MainDocumentPart.CustomXmlParts并在循环内修改元素，会导致枚举器无法同步修改后的内容，最终更新无法写入文档包。
2. 流操作与文档保存逻辑缺失：原代码未显式调用mergedDocument.Save()，仅依赖mem.Flush()无法确保OpenXML的修改完全写入内存流；同时读取流后未处理流位置，可能导致后续写入操作异常。

修正方案代码 #

public byte[] RenewCustomXmlPart(byte[] content, string customXml)
{
    using (m_log.CreateScope())
    {
        using MemoryStream mem = CreateMemoryStream(content);
        if (mem == null)
        {
            return null;
        }

        using WordprocessingDocument mergedDocument = WordprocessingDocument.Open(mem, true);
        // 先转换为列表，避免枚举时修改集合的同步问题
        var targetParts = mergedDocument.MainDocumentPart.CustomXmlParts.ToList();
        
        foreach (CustomXmlPart item in targetParts)
        {
            XDocument doc;
            using (Stream stream = item.GetStream())
            {
                doc = XDocument.Load(stream);
                stream.Position = 0; // 重置流位置，避免影响后续操作
            }
            
            if (doc.Document?.Root == null)
            {
                throw new ArgumentNullException(nameof(doc.Document.Root));
            }

            XNamespace xn = doc.Document.Root.GetDefaultNamespace();
            if (xn.NamespaceName != GlobalDefinitions.CustomXmlBausteinNamespace)
            {
                continue;
            }

            byte[] newCustomXmlBytes = Encoding.UTF8.GetBytes(customXml);
            using MemoryStream m = new(newCustomXmlBytes);
            m.Position = 0; // 确保写入流从开头开始
            item.FeedData(m);
        }

        // 显式保存文档修改到内存流
        mergedDocument.Save();
        mem.Position = 0; // 重置内存流位置，确保读取完整内容
        return mem.ToArray();
    }
}

内容的提问来源于stack exchange，提问作者Jannik