How can I debug QXmlSchema's load method? - c++

Question

I'm trying to load the following XML Schema with QXmlSchema, however QXmlSchema::load(const QUrl & source) always returns false. Is there any way to have Qt provide some about what actually went wrong? The schema checks out fine in several validators as far as I can tell (the w3c one provided mysterious output that looked like it passed).
<?xml version="1.0" ?>
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema">
<xsd:element name="message">
<xsd:complexType>
<xsd:choice>
<xsd:element name="login-reply">
<xsd:simpleType>
<xsd:restriction base="xsd:string">
<xsd:enumeration value="Accepted" />
<xsd:enumeration value="Rejected" />
</xsd:restriction>
</xsd:simpleType>
</xsd:element>
<xsd:element name="login-request" >
<xsd:complexType>
<xsd:sequence>
<xsd:element name="username" type="xsd:string" nillable="false"/>
<xsd:element name="password" type="xsd:string" nillable="false"/>
</xsd:sequence>
</xsd:complexType>
</xsd:element>
<xsd:element name="logout-request">
<xsd:complexType>
<xsd:sequence>
<xsd:element name="username" type="xsd:string" nillable="false"/>
</xsd:sequence>
</xsd:complexType>
</xsd:element>
<xsd:element name="logout-reply">
<xsd:simpleType>
<xsd:restriction base="xsd:string">
<xsd:enumeration value="Accepted" />
<xsd:enumeration value="Rejected" />
</xsd:restriction>
</xsd:simpleType>
</xsd:element>
<xsd:element name="tasklist-request" />
<xsd:element name="tasklist-reply">
<xsd:complexType>
<xsd:sequence minOccurs="1">
<xsd:element name="package" minOccurs="1" nillable="false">
<xsd:complexType>
<xsd:sequence>
<xsd:element name="taskgroup" minOccurs="1" nillable="false">
<xsd:complexType>
<xsd:sequence>
<xsd:element name="id" type="xsd:integer" minOccurs="1" />
<xsd:element name="task" type="xsd:string" minOccurs="1" />
</xsd:sequence>
<xsd:attribute name="id" type="xsd:integer" />
<xsd:attribute name="name" type="xsd:string" />
</xsd:complexType>
</xsd:element>
</xsd:sequence>
<xsd:attribute name="id" type="xsd:integer" />
<xsd:attribute name="name" type="xsd:string" />
</xsd:complexType>
</xsd:element>
</xsd:sequence>
</xsd:complexType>
</xsd:element>
<xsd:element name="starttask-request">
<xsd:complexType>
<xsd:sequence>
<xsd:element name="task-id" />
</xsd:sequence>
</xsd:complexType>
</xsd:element>
<xsd:element name="starttask-reply">
<xsd:simpleType>
<xsd:restriction base="xsd:string">
<xsd:enumeration value="Accepted" />
<xsd:enumeration value="Rejected" />
</xsd:restriction>
</xsd:simpleType>
</xsd:element>
</xsd:choice>
</xsd:complexType>
</xsd:element>
</xsd:schema>

Answer 1

bool QXmlSchema::load() itself returns only boolean result that is not really useful for debugging. But there this is more better way to get more appropriate error message.
You could use method void QXmlSchema::setMessageHandler(QAbstractMessageHandler *handler).
Here is example from my project.
First subclassing QAbstractMessageHandler
class MessageHandler : public QAbstractMessageHandler
{
public:
MessageHandler()
: QAbstractMessageHandler(),
m_messageType(QtMsgType()),
m_description(),
m_sourceLocation(QSourceLocation())
{}
QString statusMessage() const
{
return m_description;
}
qint64 line() const
{
return m_sourceLocation.line();
}
qint64 column() const
{
return m_sourceLocation.column();
}
protected:
virtual void handleMessage(QtMsgType type,
const QString &description,
const QUrl &identifier,
const QSourceLocation &sourceLocation) Q_DECL_OVERRIDE
{
Q_UNUSED(type);
Q_UNUSED(identifier);
m_messageType = type;
m_description = description;
m_sourceLocation = sourceLocation;
}
private:
QtMsgType m_messageType;
QString m_description;
QSourceLocation m_sourceLocation;
};
Then before loading set message handler.
QFile file("myschema.xsd");
file.open(QIODevice::ReadOnly);
MessageHandler messageHandler;
QXmlSchema sch;
sch.setMessageHandler(&messageHandler);
if (sch.load(&file, QUrl::fromLocalFile(file.fileName()))==false)
{
QString error = messageHandler.statusMessage();
qint64 line = messageHandler.line();
qint64 column = messageHandler.column();
/*Do what need if error*/
}

Answer 2

bool QXmlSchema::load() returns false on multiple conditions according to this source documentation
So the answer to my question: No, there is no way to get an error message from Qts parser per Qt 4.7.3 and there is no way via Qts APIs to differentiate between an I/O error and a schema error, since load returns false on both.