Can a QDeclarativeListProperty be accessed directly, instead of as a model? - qt

Question

I'm trying to use a QDeclarativeListProperty in order to manage a list of parameters, mostly for the purposes of displaying them in a ListView. However, I would also like to be able to directly access the parameters in QML from the QDeclarativeListProperty so that I can display/modify individual parameters on different screens.
My class is called ParameterClass, for which I've created a QList:
class SystemData : public QObject
{
Q_OBJECT
Q_PROPERTY(QDeclarativeListProperty<ParameterClass> parameters READ parameters CONSTANT)
QDeclarativeListProperty<ParameterClass> parameters();
...
QList<ParameterClass *> m_parameterList;
}
I've also registered the ParameterClass class and set up an instance of my SystemData as a property, which I know is necessary.
m_context->setContextProperty("SystemData", m_pSystemData);
qmlRegisterType<ParameterClass>();
Now, what I want to do within QML is something like this:
Rectangle {
id: frame
property variant parameter: SystemData.parameters[5]
...
}
I'm just not getting it to work: I keep getting back [undefined]. Am I wasting my time, or am I missing something?
Edit:
I've changed things to use the suggestion from ... . Here are some selections from my updated code.
main.cpp:
#include <QApplication>
#include <QSplashScreen>
#include <QLocale>
#include <QLibraryInfo>
#include <QDeclarativeView>
#include <QDeclarativeContext>
#include <QDeclarativeEngine>
#include <QObject>
#include <QDeclarativeListProperty>
#include "systemdata.h"
#include "parameterclass.h"
static const QString contentPath = "qrc:/qml/qml/pk_ui/";
static const QString filename(contentPath + "main.qml");
int main(int argc, char *argv[])
{
QApplication app(argc, argv);
QDeclarativeView mainView;
SystemData* systemData = SystemData::getInstance();
QThread thread;
UpdateWorker updateWorker;
QObject::connect((const QObject*)systemData, SIGNAL(startWork()),
(const QObject*)&updateWorker, SLOT(doWork()));
updateWorker.moveToThread(&thread);
thread.start();
systemData->startUpdates();
QFont defaultFont;
defaultFont.setFamily("Sans Serif");
QApplication::setFont(defaultFont);
// Register types to be available in QML
qmlRegisterType<ParameterClass>();
qmlRegisterUncreatableType<SystemEnum>("SystemEnums", 1, 0, "SystemEnum", QString());
mainView.engine()->rootContext()->setContextProperty("SystemData", systemData);
// Set view optimizations not already done for QDeclarativeView
mainView.setResizeMode(QDeclarativeView::SizeRootObjectToView);
mainView.setAttribute(Qt::WA_OpaquePaintEvent);
mainView.setAttribute(Qt::WA_NoSystemBackground);
mainView.setSource(QUrl(filename));
mainView.show();
return app.exec();
}
The ParameterClass looks like this:
class ParameterClass : public QObject
{
Q_OBJECT
Q_PROPERTY(int type READ get_type NOTIFY typeChanged)
Q_PROPERTY(bool enabled READ get_ParameterEnabled WRITE set_ParameterEnabled NOTIFY enabledChanged)
Q_PROPERTY(int groupID READ get_GroupID WRITE set_GroupID NOTIFY groupIDChanged)
Q_PROPERTY(int unitID READ get_UnitID WRITE set_UnitID NOTIFY unitIDChanged)
Q_PROPERTY(int securityLevel READ get_SecurityLevel WRITE set_SecurityLevel NOTIFY securityLevelChanged)
Q_PROPERTY(QString parameterName READ get_ParameterName NOTIFY parameterNameChanged)
Q_PROPERTY(QString shortDescription READ get_ShortDescription NOTIFY shortDescriptionChanged)
Q_PROPERTY(int currentValue READ get_CV WRITE set_valueptrvalue NOTIFY currentValueChanged)
Q_PROPERTY(int lowerBound READ get_LB NOTIFY lowerBoundChanged)
Q_PROPERTY(int upperBound READ get_UB NOTIFY upperBoundChanged)
public:
struct ValueTypes
{
enum
{
IntegerType,
StringType,
StringListType
};
};
ParameterClass(QObject *parent = 0);
int get_type();
bool get_ParameterEnabled();
int get_GroupID();
int get_UnitID();
int get_SecurityLevel();
QString get_ParameterName();
QString get_ShortDescription();
int get_CV() { return *CurrentValuePtr; }
int get_LB() { return *LowerBoundPtr; }
int get_UB() { return *UpperBoundPtr; }
void set_ParameterEnabled(bool InParameterEnabled);
void set_GroupID(int InGroupID);
void set_UnitID(int InUnitID);
void set_SecurityLevel(int InSecurityLevel);
signals:
void typeChanged();
void enabledChanged();
void groupIDChanged();
void unitIDChanged();
void securityLevelChanged();
void parameterNameChanged();
void shortDescriptionChanged();
private:
int type;
bool ParameterEnabled;
int GroupID;
int UnitID;
int SecruityLevel;
QString ParameterName;
QString ShortDescription;
int * CurrentValuePtr;
int * LowerBoundPtr;
int * UpperBoundPtr;
};
And my QML file:
Rectangle {
id: frame
property int val: SystemData.parameters[4].currentValue
...
}
It looks like I'm still getting an undefined value in this case. I'm trying to debug now, so that I can provide more information.

Answer 1

It's very much possible. The key is to make sure you register the QML type and set the context property before setting the source on your QDeclarativeView.
Here's a working example -
main.cpp:
#include <QApplication>
#include <QtDeclarative>
class MyPropertyObject : public QObject {
Q_OBJECT
Q_PROPERTY(int value READ value CONSTANT)
public:
MyPropertyObject(int value = -1) : m_value(value) { }
int value() const {
return m_value;
}
private:
int m_value;
};
class MyObject : public QObject {
Q_OBJECT
Q_PROPERTY(QDeclarativeListProperty<MyPropertyObject> props READ props CONSTANT)
public:
MyObject() {
m_props.append(new MyPropertyObject(55));
m_props.append(new MyPropertyObject(44));
m_props.append(new MyPropertyObject(33));
}
QDeclarativeListProperty<MyPropertyObject> props() {
return QDeclarativeListProperty<MyPropertyObject>(this, m_props);
}
private:
QList<MyPropertyObject *> m_props;
};
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
QDeclarativeView view;
view.engine()->rootContext()->setContextProperty(QLatin1String("tester"), new MyObject);
qmlRegisterType<MyPropertyObject>();
view.setSource(QUrl("qrc:///qml/main.qml"));
view.setResizeMode(QDeclarativeView::SizeRootObjectToView);
view.resize(300, 300);
view.show();
return a.exec();
}
#include "main.moc"
main.qml:
import QtQuick 1.1
Rectangle {
property variant foo: tester.props[2].value
Text {
anchors.centerIn: parent
text: parent.foo
}
}
Note: read the docs for the QDeclarativeListProperty constructors. The one I'm using for this example is not the preferred one, but is good for quick prototypes.