xml - 在 Delphi XE2 中解析 XML 时出现访问冲突

Question

我正在尝试使用以下代码在 Delphi XE2 中解析 MusicBraninz XML 文件:

webquery := 'http://www.musicbrainz.org/ws/2/recording/?query='+escape(tracktitle)+'&artist:'+escape(ArtistTitle);

Log('WebQuery: ' + webquery, 0);

begin
  XMLDoc:= TXMLDocument.Create(nil);
  XMLDoc.FileName := webQuery;
  XMLDoc.Active := True;

  Log('Report: ' + XMLDoc.XML.Text, 0);


   StartItemNode := XMLDoc.DocumentElement.ChildNodes.First.ChildNodes.FindNode('release-list') ;

   ANode := StartItemNode;
   repeat
     Result.Album := ANode.ChildNodes['title'].Text;  <-- Access Violation
     Result.Status:= ANode.ChildNodes['status'].Text;

     ANode := ANode.NextSibling;
   until ANode = nil;

end;

XML 文件已正确获取，如下所示:

<metadata xmlns="http://musicbrainz.org/ns/mmd-2.0#" xmlns:ext="http://musicbrainz.org/ns/ext#-2.0">
<recording-list offset="0" count="1">
<recording ext:score="100" id="a399eec1-d45d-4505-b475-ead0da6cad17">
<title>Mestecăniș</title>
<length>359000</length>
<artist-credit>
<name-credit>
<artist id="8fb78a16-0cba-4175-8c92-d9645dfb007d">
<name>Bucovina</name>
<sort-name>Bucovina</sort-name>
</artist>
</name-credit>
</artist-credit>
<release-list>
<release id="22b00afc-86ea-445a-8805-b6bfa33da74e">
<title>Duh</title>
<status>Official</status>
<release-group type="EP" id="4e8fb87c-3760-48c1-a3d7-88e7a2c839fa">
<primary-type>EP</primary-type>
</release-group>
<date>2010</date>
<country>RO</country>
<medium-list>
<track-count>5</track-count>
<medium>
<position>1</position>
<format>CD</format>
<track-list offset="3" count="5">
<track>
<number>4</number>
<title>Mestecăniș</title>
<length>359000</length>
</track>
</track-list>
</medium>
</medium-list>
</release>
</release-list>
</recording>
</recording-list>
</metadata>

我的问题是:我在这里做错了什么吗？所有变量都已声明并初始化完毕。

谢谢

Answer 1

您遇到访问冲突，因为 FindNode 方法返回 nil 值，并且您正在尝试访问无效的内存位置。为了使用 FindNode 方法，您必须检查要搜索的节点的层次结构(级别)，然后检查结果是否不 nil。

尝试这个示例。

  XMLDoc:= LoadXMLDocument(webQuery);
   StartItemNode := XMLDoc.DocumentElement.ChildNodes.FindNode('recording-list');
   if not Assigned(StartItemNode) then exit;
   StartItemNode := StartItemNode.ChildNodes.FindNode('recording');
   if Assigned(StartItemNode) then
   begin
     StartItemNode := StartItemNode.ChildNodes.FindNode('release-list');
     if Assigned(StartItemNode) then
     begin
       StartItemNode := StartItemNode.ChildNodes.FindNode('release');
       if Assigned(StartItemNode) then
       begin
         ANode := StartItemNode;
         repeat
           Result.Album := ANode.ChildNodes['title'].Text;
           Result.Status:= ANode.ChildNodes['status'].Text;
           ANode := ANode.NextSibling;
         until ANode = nil;
       end;
     end;
   end;