System.Xml.Serialization.XmlSerializationWriter.WriteNamespaceDeclarations C# (CSharp) Method

        protected void WriteNamespaceDeclarations(XmlSerializerNamespaces xmlns)
        {
            if (xmlns != null)
            {
                foreach (KeyValuePair<string, string> entry in xmlns.Namespaces)
                {
                    string prefix = (string)entry.Key;
                    string ns = (string)entry.Value;
                    if (_namespaces != null)
                    {
                        string oldNs = _namespaces.Namespaces[prefix] as string;
                        if (oldNs != null && oldNs != ns)
                        {
                            throw new InvalidOperationException(SR.Format(SR.XmlDuplicateNs, prefix, ns));
                        }
                    }
                    string oldPrefix = (ns == null || ns.Length == 0) ? null : Writer.LookupPrefix(ns);

                    if (oldPrefix == null || oldPrefix != prefix)
                    {
                        WriteAttribute(nameof(xmlns), prefix, null, ns);
                    }
                }
            }
            _namespaces = null;
        }