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Finding elements with XPath in Delphi

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佛祖请我去吃肉
佛祖请我去吃肉 2021-01-16 11:12

I am trying to find an element in an XML document in Delphi. I have this code, but it always says 0 elements in the log:

function TForm1.KannaSidu: Boolean;
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  • 灰色年华
    2021-01-16 11:54

    In the example code I find online for the selectNodes method, it is preceded by code that sets the document's SelectionNamespaces property via setProperty. Some even set SelectionLanguage, too.

    Doc.setProperty('SelectionLanguage', 'XPath');
Doc.setProperty('SelectionNamespaces',
  'xmlns:xsl=''http://www.w3.org/1999/XSL/Transform''');

    Based on the element names you're searching for, I guess you're processing an HTML file. The basic HTML elements are in the http://www.w3.org/1999/xhtml namespace, so try this:

    Doc.setProperty('SelectionNamespaces',
  'xmlns:x=''http://www.w3.org/1999/xhtml''');
List := Doc.selectNodes('/x:html/x:head');

    See also:

    selectNodes does not give node list when xmlns is used on Microsoft's forum.

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  • 耶瑟儿～
    2021-01-16 12:03

    If you're just trying to load a plain html file as xml, it would probably have multiple reasons to fail and choke on things like:

    <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">

    You have to test that it actually loads correctly before doing anything else:

      if not Doc.load(filename) then
    raise Exception.Create('XML Loading error:' + Trim(Doc.parseError.reason));

    It will give you the specific reason for the failure like this one:

    XML Loading error:End tag 'head' does not match the start tag 'link'.
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  • 慢半拍i
    2021-01-16 12:07

    IXMLDOMDocument.Load() does not raise an exception if something goes wrong with your file or with its content. Try the following to be sure there is nothing bad with it:

    ...
Doc.load(Filename);
if Doc.parseError.errorCode <> 0 then
  ShowMessage('Error : ' + + Doc.parseError.reason) 
else
  ShowMessage('No problem so far !');
...

    I suck at XPath but maybe if html is your root node you don't need to include it in your query string, so try the following :

    List:=Doc.selectNodes('//html/head');

    or

    List:=Doc.selectNodes('//head');
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