Problem reading an Xml file with QXmlStreamReader

[annatz]

Ηi,
The code that follows reads a file and if a patient already exists, shows an error message, otherwise it calls the function
CreateXMLFile. The problem is that it gets in the while loop only once and the value of the id2 is always the same.
What can i do?

@void QXSRExample::ReadXMLFile(){
flag=0;
QFile* file = new QFile("c:/anna.xml");
if (!file->open(QIODevice::ReadWrite | QIODevice::Text)) {
QMessageBox::critical(this,
"QXSRExample::ReadXMLFile",
"Couldn't open anna.xml",
QMessageBox::Ok);
return;
}
QXmlStreamReader xml(file);
while(!xml.atEnd() ) {
if(xml.name() == "patient_id") {
id2=xml.readElementText();
if (itemId==id2)
flag=1;}
xml.readNext();
}
xml.clear();
if (flag==1)
QMessageBox::warning(this,"Error","O asthenis einai idi kataxwrimenos",QMessageBox::Ok);
else
CreateXMLFile();
file->close();
}

void QXSRExample::CreateXMLFile(){
//Anoigma tou arxeiou
QString filename = ("c:/anna.xml");
QFile file2(filename);
if (!file2.open(QIODevice::Append | QIODevice::Text)){
//emfanisi sxetikou minimatos gia sfalma
QMessageBox::warning(0, "Write only", "The file is in write only mode");}
QXmlStreamWriter* xmlWriter = new QXmlStreamWriter();
xmlWriter->setDevice(&file2);
xmlWriter->writeStartElement("examinations");
xmlWriter->writeStartElement("patient_exams");
xmlWriter->writeStartElement("patient_id");
xmlWriter->writeCharacters (itemId);
xmlWriter->writeEndElement();
……………etc
@

[andre]

Please, reformat your code to use proper, consistent indenting. That will make it much easier to spot the issue you are running into.

I really don't get the logic of starting to write an XML file while trying to read that same file. How is that supposed to work?

[annatz]

first i read the file to see if there is a patient with the same id. if there isn't a patient with that id i write to the file the examinations for that patient.

i don't understand how to make my code

[andre]

I mean a formatting like below, makes your code more readable and thus makes it easier to spot what is going wrong.

@
void QXSRExample::ReadXMLFile(){
flag=0;
QFile* file = new QFile("c:/anna.xml");
if (!file->open(QIODevice::ReadWrite | QIODevice::Text)) {
QMessageBox::critical(this,
"QXSRExample::ReadXMLFile",
"Couldn't open anna.xml",
QMessageBox::Ok);
return;
}
QXmlStreamReader xml(file);
while(!xml.atEnd() ) {
if(xml.name() == "patient_id") {
id2=xml.readElementText();
if (itemId==id2)
flag=1;
}
xml.readNext();
}
xml.clear();
if (flag==1)
QMessageBox::warning(this,"Error","O asthenis einai idi kataxwrimenos",QMessageBox::Ok);
else
CreateXMLFile();
file->close();
}
@

I don't think it is a good idea to try to write to a file from the function that is supposed to read from it. IMHO, it is better to separate that into different functions, and don't call the one from the other.

[annatz]

In that way i had done the format of the code.

ok, i will seperate the two functions but you didnt response to my problem.

The problem is that it gets in the while loop only once and the value of the id2 is always the same.
it doesnt read the next patient_id

[andre]

[quote author="annatz" date="1314113534"]In that way i had done the format of the code.[/quote]
But that is not what you posted, so not what we could see and study.
[quote]
ok, i will seperate the two functions but you didnt response to my problem.

The problem is that it gets in the while loop only once and the value of the id2 is always the same.
it doesnt read the next patient_id
[/quote]

Could you post the XML that you are trying to read then? We can not check if the code is at fault in this case.

[annatz]

i write the xml but at the preview it is different.

@
<examinations>
<patient_exams>
<patient_id>1</patient_id>
<lab_test>
<lab_id>Mikro</lab_id>
<test_id>UREA</test_id>
<specimen>blood</specimen>
</lab_test>
</patient_exams>
</examinations>
@

the number 1 that is after examinations is after patient_id. and after examinations is the tag patient_exams

Edit: reformatted XML to make it more readable. Please do that yourself next time; Andre

[andre]

With the above piece of XML, and the code that you showed, you will encounter the patient_id tag twice: once for the openening, and once for the closing tag. id2 will contain the text "1" on the first call, and be empty for the second (read the docs on readElementText for an explanation why).

It is obviously always the same, because the XML does not change all of a sudden during the reading (that is: you should not change the XML, as I told you before).

[lgeyer]

Have you considered using "QDomDocument":http://doc.qt.nokia.com/latest/qdomdocument.html instead?

This will create an in-memory representation of your XML document which allows for searching and inserting / removing nodes.

[andre]

Yes, but QDomDocument is considdered EOL and is thus not wise to use in new code.

[annatz]

I change my code like this:

@void QXSRExample::ReadXMLFile(){
flag=0;
QFile* file = new QFile("c:/anna.xml");
if (!file->open(QIODevice::ReadWrite | QIODevice::Text)) {
QMessageBox::critical(this,
"QXSRExample::ReadXMLFile",
"Couldn't open anna.xml",
QMessageBox::Ok);
return;
}
QXmlStreamReader xml(file);
while(!xml.atEnd() && !xml.hasError()){
QXmlStreamReader::TokenType token = xml.readNext();
if(token == QXmlStreamReader::StartDocument)
continue;
while(!(xml.tokenType() == QXmlStreamReader::EndElement && xml.name() == "patient_id")) {
if(xml.tokenType() == QXmlStreamReader::StartElement) {
if(xml.name() == "patient_id") {
id2=xml.readElementText();
if (itemId==id2)
flag=1;
}
}
xml.readNextStartElement();
}
}
xml.clear();
if (flag==1)
QMessageBox::warning(this,"Error","O asthenis einai idi kataxwrimenos",QMessageBox::Ok);
else
CreateXMLFile();
file->close();
}@

but now the program craches.

[andre]

Again: please make your code easy to read here. Take care of indentation and the likes.

Then, your code looks like nonsense. First you iterate through the whole XML in search of a StartDocument tag, and then you do nothing with it. Then, you expect there is more to read?
A crash is easy to debug usually. Your debugger will tell what line triggered the crash.

[lgeyer]

[quote author="Andre" date="1314164753"]Yes, but QDomDocument is considdered EOL and is thus not wise to use in new code. [/quote]

It is? It is not listed as deprecated in the documentation and the "module maturiy list":http://labs.qt.nokia.com/2011/05/12/qt-modules-maturity-level-the-list/ also states it as done (not deprecated). Is there another source to look at when evaluating module lifetime?

[goetz]

XML DOM should never be EOL. It is the only means to manipulate an XML document in-memory. And sometimes there are cases where you just plain cannot use a stream writer, e.g. when you need to add nodes at two different places in the tree simultaneously.

[andre]

Let me put it this way: if I am wrong, then Thiago was wrong. He's the one saying something along these lines, but I can not remember if it was on IRC or on the mailinglist.

[goetz]

Maybe it's EOL in the sense of "no new features". But there's far too much code out there that relies on QDom. One should consider the stream classes for new projects, though.

[andre]

EOL as in: no new features, no real maintenance (only grave bugs might get fixed), and no longer the recommended way to do things. Of course, not as: will be removed. That's how I understood it, at least.

[annatz]

I changed my code.
It doesnt matter that the program will find twice the tag patient_id.
The problem is that in the xml file are the same tags (from examinations to /examinations) many times, and i tried to debug my code and i saw that my code reads the xml (from examinatios to /examinations) only once. it "thinks" that it is the end of the file but it isnt ( it has more tags).

@
while(!xml.atEnd() && !xml.hasError()){
if (xml.name() == "patient_id") {
id2=xml.readElementText();
if (itemId==id2)
flag=1;
}
xml.readNext();
}
@

[annatz]

Hi,

I have created some checkboxes with some examinations.

@checkbox1 = new QCheckBox("Geniki Aimatos", this);
checkbox2 = new QCheckBox("UREA", this);
checkbox3 = new QCheckBox("CREA", this);@

but i want to change my code and read the examinations from an xml file. the xml may change in the future.It may be bigger.
So how can i create the checkboxes? each checkbox should have a different name. if i count the examinations of the file, how can i define the checkboxes?

2 replies
November 7, 2011
Lukas Geyer Lukas Geyer
Gene Splicer
736 posts

Groupie L1

 
|report

Use QXmlStreamReader to read the XML, create QCheckBoxes on the fly and add them to a layout, for example a QVBoxLayout to have them aligned properly. Use setObjectName() to associate a unique identifier with each checkbox.

---

I did what you said (Lucas), but can you explain me how to use the setObjectName() please?
i can't find any documentation.

my code is :
QCheckBox* checkbox1=new QCheckBox();
@File* file = new QFile("c:/exetaseis.xml");
if (!file->open(QIODevice::ReadOnly | QIODevice::Text)) {
QMessageBox::critical(this,
"QXSRExample::ok",
"Couldn't open exetaseis.xml",
QMessageBox::Ok);
return;
}

QXmlStreamReader xml(file);
while (!xml.atEnd() && !xml.hasError()) {
if(xml.tokenType() == QXmlStreamReader::StartElement)
if (xml.name() == "lab_test"){
arithmos_exetasewn++;
checkbox1->setObjectName("check");
}
}

xml.readNext();

_layout2->addWidget(checkbox1);
@

Is the way I used the setobjectname correct? and then i should use sth like this
@QList<QCheckBox *> allCheckboxes=checkbox1->findChildren<QCheckBox *>();
@

[goetz]

[quote author="annatz" date="1320921838"]
I did what you said (Lucas), but can you explain me how to use the setObjectName() please?
i can't find any documentation.
[/quote]

Then you did not search properly. Here "it is":http://doc.qt.nokia.com/4.7/qobject.html#objectName-prop

Just as a side note: Use Qt Assistant (it's installed with every Qt) for searching the docs. And you did spot the DOC tab here on DevNet already, didn't you? It has a search function too.