System.Xml.XmlBaseWriter.NamespaceManager.LookupPrefix C# (CSharp) Méthode

            public string LookupPrefix(string ns)
            {
                if (_lastNameSpace != null && _lastNameSpace.Uri == ns)
                    return _lastNameSpace.Prefix;
                int nsCount = _nsCount;
                for (int i = nsCount - 1; i >= _nsTop; i--)
                {
                    Namespace nameSpace = _namespaces[i];
                    if (object.ReferenceEquals(nameSpace.Uri, ns))
                    {
                        string prefix = nameSpace.Prefix;
                        // Make sure that the prefix refers to the namespace in scope
                        bool declared = false;
                        for (int j = i + 1; j < nsCount; j++)
                        {
                            if (_namespaces[j].Prefix == prefix)
                            {
                                declared = true;
                                break;
                            }
                        }
                        if (!declared)
                        {
                            _lastNameSpace = nameSpace;
                            return prefix;
                        }
                    }
                }
                for (int i = nsCount - 1; i >= _nsTop; i--)
                {
                    Namespace nameSpace = _namespaces[i];
                    if (nameSpace.Uri == ns)
                    {
                        string prefix = nameSpace.Prefix;
                        // Make sure that the prefix refers to the namespace in scope
                        bool declared = false;
                        for (int j = i + 1; j < nsCount; j++)
                        {
                            if (_namespaces[j].Prefix == prefix)
                            {
                                declared = true;
                                break;
                            }
                        }
                        if (!declared)
                        {
                            _lastNameSpace = nameSpace;
                            return prefix;
                        }
                    }
                }

                if (ns.Length == 0)
                {
                    // Make sure the default binding is still valid
                    bool emptyPrefixUnassigned = true;
                    for (int i = nsCount - 1; i >= _nsTop; i--)
                    {
                        if (_namespaces[i].Prefix.Length == 0)
                        {
                            emptyPrefixUnassigned = false;
                            break;
                        }
                    }
                    if (emptyPrefixUnassigned)
                        return string.Empty;
                }

                if (ns == xmlnsNamespace)
                    return "xmlns";
                if (ns == xmlNamespace)
                    return "xml";
                return null;
            }