How to print a list of custom properties of a QML object?
By creating a QML QtObject:
QtObject {
property int p: 42
property int q: 44
}
Once you have saved in a local variable QObject *obj
, how to print the names of all the custom properties and possibly value (ie only p
and q
for the above example)? I would like this to work for any class (not just QtObject
), not print properties that have already been declared with Q_PROPERTY
.
Clarification: by "custom" I do not mean properties added via QObject::setProperty
that were not declared with Q_PROPERTY
. I mean properties declared in QML via note property <type> <name>: <value>
that were not declared using Q_PROPERTY
in a subclass QObject
for this QML object. A quick test shows that these properties do not appear in the QObject::dynamicPropertyNames
.
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All property information, invokable methods (slots too) and signals are stored by the QMetaObject in each QObject . If you want to list all properties of an object:
QObject *obj = findObjectMethod();
QMetaObject *meta = obj->metaObject();
int n = meta->propertyCount();
for(int i = 0; i < n; ++i)
{
qDebug() << "Property: " << meta->property(i)->name();
}
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C ++ and QML approach
To print only dynamic property names, you can use the very aptly named dynamicPropertyNames ()QObject
function from from within the calling C ++ function
#include <QGuiApplication>
#include <QtQml>
class Object : public QObject
{
Q_OBJECT
Q_PROPERTY(int staticProperty READ staticProperty)
public:
Object() {
setProperty("dynamicProperty", 1);
}
int staticProperty() const {
return 0;
}
Q_INVOKABLE void printDynamicPropertyNames() const {
qDebug() << dynamicPropertyNames();
}
};
int main(int argc, char** argv)
{
QGuiApplication app(argc, argv);
Object object;
QQmlApplicationEngine engine;
engine.rootContext()->setContextProperty("object", &object);
engine.load("main.qml");
return app.exec();
}
#include "main.moc"
main.qml:
import QtQuick 2.3
import QtQuick.Controls 1.2
ApplicationWindow {
width: 400
height: 400
visible: true
Component.objectName: object.printDynamicPropertyNames()
}
Output:
("dynamicProperty")
QML approach only
If you want to print all properties of an object, dynamic or not, exclusively with QML, use the JavaScript for ... in syntax:
The for..in operator iterates over the enumerated properties of an object in no particular order. For each individual property, statements can be executed.
import QtQuick 2.2
Rectangle {
id: rect
width: 360
height: 360
Component.onCompleted: {
for (var prop in rect) {
print(prop += " (" + typeof(rect[prop]) + ") = " + rect[prop]);
}
}
}
Output:
qml: objectName (string) =
qml: parent (object) = null
qml: data (object) = [object Object]
qml: resources (object) = [object Object]
qml: children (object) = [object Object]
qml: x (number) = 0
qml: y (number) = 0
qml: z (number) = 0
qml: width (number) = 360
qml: height (number) = 360
qml: opacity (number) = 1
qml: enabled (boolean) = true
...
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