[Qt-interest] QXmlStreamReader: Usage of readNextStartElement()?

[David Bowman]

Oliver,

I believe readNextStartElement recursively goes down through the
elements, as bar does not have any children readNextStart will return
false. If you call skipCurrentElement on a childless element it should
jump it back up a level.

See the xmlstream bookmarks example in the qt docs.

Regards,
David

-----Original Message-----
From: qt-interest-bounces+david.bowman=iongeo.com at qt.nokia.com
[mailto:qt-interest-bounces+david.bowman=iongeo.com at qt.nokia.com] On
Behalf Of Oliver.Knoll at comit.ch
Sent: 21 December 2010 17:07
To: qt-interest at trolltech.com
Subject: [Qt-interest] QXmlStreamReader: Usage of
readNextStartElement()?

Hi,

I am having difficulties understanding the proper usage of
QXmlStreamReader#readNextStartElement():

When I have the following code snippet which should print out all
element names and attributes:

  QXmlStreamReader streamReader(&file);
  while (streamReader.readNextStartElement()) {

    qDebug("name: %s", qPrintable(streamReader.name().toString()));
    QXmlStreamAttributes attributes = streamReader.attributes();
    foreach(QXmlStreamAttribute attribute, attributes) {
      qDebug("    Attribute: name: %s, value: %s",
qPrintable(attribute.name().toString()),
qPrintable(attribute.value().toString()));
    }

  }

And I have e.g.

  <?xml version="1.0" encoding="UTF-8"?>
  <!DOCTYPE screenie>
  <foo version="1.0">
    <bar enabled="true" bgcolor="#ffffff"/>
    <foobar baz="42"/>
    <rabarber>Some text</rabarber>
  </foo>

I only get:

name: foo
    Attribute: name: version, value: 1.0
name: bar
    Attribute: name: enabled, value: true
    Attribute: name: bgcolor, value: #ffffff

That is the parsing seems to stop after the 2nd element <bar .../>.

>From the Qt docs
http://doc.trolltech.com/4.7/qxmlstreamreader.html#readNextStartElement:
"Reads until the next start element within the current element. [...]The
current element is the element matching the most recently parsed start
element of which a matching end element has not yet been reached."

So let's assume that <foo> - the outermost "start element" as it seems
to me - is the "current element", should I not get also the <foobar />
and <rababer /> elements? What really twists my mind is that I /do/ get
the <bar> element, but why not the <foobar> and <rabarber> elements,
which are at the same level as <bar>? So the time when
readNextStartElement seems to stop is a mistery to me...


If on the other hand I iterate over the XML like this with readNext():

  while ((tokenType = streamReader.readNext()) !=
QXmlStreamReader::EndDocument) {
    if (tokenType == QXmlStreamReader::StartElement) {
      qDebug("name: %s", qPrintable(streamReader.name().toString()));
      QXmlStreamAttributes attributes = streamReader.attributes();
      foreach(QXmlStreamAttribute attribute, attributes) {
        qDebug("    Attribute: name: %s, value: %s",
qPrintable(attribute.name().toString()),
qPrintable(attribute.value().toString()));
      }
    }

I do get all elements as expected.


The only difference between my readNextStartElement() version and the
http://doc.trolltech.com/4.7/xml-streambookmarks.html example seems to
be that in the later they do a readElementText() and a
skipCurrentElement() in between (and this example seems to work for me,
at least with a simple *.xbel bookmark file. I have yet to try out a
more complex one, e.g. with several "folders" or so). But other than
that also this Qt example seems to simply iterate over the entire XML
with readNextStartElement().


So what am I doing wrong? Is this supposed to work like I assume, or is
this a bug? This is on Qt 4.7.1. Example code and test file attached.

Cheers, Oliver





-- 
Oliver Knoll
Dipl. Informatik-Ing. ETH
COMIT AG - ++41 79 520 95 22


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