QQmlProperty Class

The QQmlProperty class abstracts accessing properties on objects created from QML. More...

Header:	#include <QQmlProperty>
CMake:	find_package(Qt6 COMPONENTS Qml REQUIRED) target_link_libraries(mytarget PRIVATE Qt6::Qml)
qmake:	QT += qml
Since:	Qt 5.0

• List of all members, including inherited members

Public Types

enum	PropertyTypeCategory { InvalidCategory, List, Object, Normal }
enum	Type { Invalid, Property, SignalProperty }

Public Functions

	QQmlProperty(const QQmlProperty &other)
	QQmlProperty(QObject *obj, const QString &name, QQmlEngine *engine)
	QQmlProperty(QObject *obj, const QString &name, QQmlContext *ctxt)
	QQmlProperty(QObject *obj, const QString &name)
	QQmlProperty(QObject *obj, QQmlEngine *engine)
	QQmlProperty(QObject *obj, QQmlContext *ctxt)
	QQmlProperty(QObject *obj)
	QQmlProperty()
QQmlProperty &	operator=(const QQmlProperty &other)
bool	connectNotifySignal(QObject *dest, const char *slot) const
bool	connectNotifySignal(QObject *dest, int method) const
bool	hasNotifySignal() const
int	index() const
bool	isDesignable() const
bool	isProperty() const
bool	isResettable() const
bool	isSignalProperty() const
bool	isValid() const
bool	isWritable() const
QMetaMethod	method() const
QString	name() const
bool	needsNotifySignal() const
QObject *	object() const
QMetaProperty	property() const
QMetaType	propertyMetaType() const
int	propertyType() const
QQmlProperty::PropertyTypeCategory	propertyTypeCategory() const
const char *	propertyTypeName() const
QVariant	read() const
bool	reset() const
QQmlProperty::Type	type() const
bool	write(const QVariant &value) const
bool	operator==(const QQmlProperty &other) const

Static Public Members

QVariant	read(const QObject *object, const QString &name)
QVariant	read(const QObject *object, const QString &name, QQmlContext *ctxt)
QVariant	read(const QObject *object, const QString &name, QQmlEngine *engine)
bool	write(QObject *object, const QString &name, const QVariant &value)
bool	write(QObject *object, const QString &name, const QVariant &value, QQmlContext *ctxt)
bool	write(QObject *object, const QString &name, const QVariant &value, QQmlEngine *engine)

Detailed Description

As QML uses Qt's meta-type system all of the existing QMetaObject classes can be used to introspect and interact with objects created by QML. However, some of the new features provided by QML - such as type safety and attached properties - are most easily used through the QQmlProperty class that simplifies some of their natural complexity.

Unlike QMetaProperty which represents a property on a class type, QQmlProperty encapsulates a property on a specific object instance. To read a property's value, programmers create a QQmlProperty instance and call the read() method. Likewise to write a property value the write() method is used.

For example, for the following QML code:

// MyItem.qml
import QtQuick 2.0

Text { text: "A bit of text" }

The Text object's properties could be accessed using QQmlProperty, like this:

#include <QQmlProperty>
#include <QGraphicsObject>

...

QQuickView view(QUrl::fromLocalFile("MyItem.qml"));
QQmlProperty property(view.rootObject(), "font.pixelSize");
qWarning() << "Current pixel size:" << property.read().toInt();
property.write(24);
qWarning() << "Pixel size should now be 24:" << property.read().toInt();

Member Type Documentation

enum QQmlProperty::PropertyTypeCategory

This enum specifies a category of QML property.

Constant	Value	Description
QQmlProperty::InvalidCategory	0	The property is invalid, or is a signal property.
QQmlProperty::List	1	The property is a QQmlListProperty list property
QQmlProperty::Object	2	The property is a QObject derived type pointer
QQmlProperty::Normal	3	The property is a normal value property.

enum QQmlProperty::Type

This enum specifies a type of QML property.

Constant	Value	Description
QQmlProperty::Invalid	0	The property is invalid.
QQmlProperty::Property	1	The property is a regular Qt property.
QQmlProperty::SignalProperty	2	The property is a signal property.

Member Function Documentation

QQmlProperty::QQmlProperty(const QQmlProperty &other)

Create a copy of other.

QQmlProperty::QQmlProperty(QObject *obj, const QString &name, QQmlEngine *engine)

Creates a QQmlProperty for the property name of obj using the environment for instantiating QML components that is provided by engine.

QQmlProperty::QQmlProperty(QObject *obj, const QString &name, QQmlContext *ctxt)

Creates a QQmlProperty for the property name of obj using the context ctxt.

Creating a QQmlProperty without a context will render some properties - like attached properties - inaccessible.

QQmlProperty::QQmlProperty(QObject *obj, const QString &name)

Creates a QQmlProperty for the property name of obj.

QQmlProperty::QQmlProperty(QObject *obj, QQmlEngine *engine)

Creates a QQmlProperty for the default property of obj using the environment for instantiating QML components that is provided by engine. If there is no default property, an invalid QQmlProperty will be created.

QQmlProperty::QQmlProperty(QObject *obj, QQmlContext *ctxt)

Creates a QQmlProperty for the default property of obj using the context ctxt. If there is no default property, an invalid QQmlProperty will be created.

QQmlProperty::QQmlProperty(QObject *obj)

Creates a QQmlProperty for the default property of obj. If there is no default property, an invalid QQmlProperty will be created.

QQmlProperty::QQmlProperty()

Create an invalid QQmlProperty.

QQmlProperty &QQmlProperty::operator=(const QQmlProperty &other)

Assign other to this QQmlProperty.

bool QQmlProperty::connectNotifySignal(QObject *dest, const char *slot) const

Connects the property's change notifier signal to the specified slot of the dest object and returns true. Returns false if this metaproperty does not represent a regular Qt property or if it has no change notifier signal, or if the dest object does not have the specified slot.

bool QQmlProperty::connectNotifySignal(QObject *dest, int method) const

Connects the property's change notifier signal to the specified method of the dest object and returns true. Returns false if this metaproperty does not represent a regular Qt property or if it has no change notifier signal, or if the dest object does not have the specified method.

bool QQmlProperty::hasNotifySignal() const

Returns true if the property has a change notifier signal, otherwise false.

int QQmlProperty::index() const

Return the Qt metaobject index of the property.

bool QQmlProperty::isDesignable() const

Returns true if the property is designable, otherwise false.

bool QQmlProperty::isProperty() const

Returns true if this QQmlProperty represents a regular Qt property.

bool QQmlProperty::isResettable() const

Returns true if the property is resettable, otherwise false.

bool QQmlProperty::isSignalProperty() const

Returns true if this QQmlProperty represents a QML signal property.

bool QQmlProperty::isValid() const

Returns true if the QQmlProperty refers to a valid property, otherwise false.

bool QQmlProperty::isWritable() const

Returns true if the property is writable, otherwise false.

QMetaMethod QQmlProperty::method() const

Return the QMetaMethod for this property if it is a SignalProperty, otherwise returns an invalid QMetaMethod.

QString QQmlProperty::name() const

Return the name of this QML property.

Note: Getter function for property name.

bool QQmlProperty::needsNotifySignal() const

Returns true if the property needs a change notifier signal for bindings to remain upto date, false otherwise.

Some properties, such as attached properties or those whose value never changes, do not require a change notifier.

QObject *QQmlProperty::object() const

Returns the QQmlProperty's QObject.

Note: Getter function for property object.

QMetaProperty QQmlProperty::property() const

Returns the Qt property associated with this QML property.

QMetaType QQmlProperty::propertyMetaType() const

Returns the metatype of the property.

See also propertyType.

int QQmlProperty::propertyType() const

Returns the metatype id of the property, or QMetaType::UnknownType if the property has no metatype.

See also propertyMetaType.

QQmlProperty::PropertyTypeCategory QQmlProperty::propertyTypeCategory() const

Returns the property category.

const char *QQmlProperty::propertyTypeName() const

Returns the type name of the property, or 0 if the property has no type name.

QVariant QQmlProperty::read() const

Returns the property value.

[static] QVariant QQmlProperty::read(const QObject *object, const QString &name)

Return the name property value of object. This method is equivalent to:

QQmlProperty p(object, name);
p.read();

[static] QVariant QQmlProperty::read(const QObject *object, const QString &name, QQmlContext *ctxt)

Return the name property value of object using the context ctxt. This method is equivalent to:

QQmlProperty p(object, name, context);
p.read();

[static] QVariant QQmlProperty::read(const QObject *object, const QString &name, QQmlEngine *engine)

Return the name property value of object using the environment for instantiating QML components that is provided by engine. . This method is equivalent to:

QQmlProperty p(object, name, engine);
p.read();

bool QQmlProperty::reset() const

Resets the property and returns true if the property is resettable. If the property is not resettable, nothing happens and false is returned.

QQmlProperty::Type QQmlProperty::type() const

Returns the type of the property.

bool QQmlProperty::write(const QVariant &value) const

Sets the property value to value. Returns true on success, or false if the property can't be set because the value is the wrong type, for example.

[static] bool QQmlProperty::write(QObject *object, const QString &name, const QVariant &value)

Writes value to the name property of object. This method is equivalent to:

QQmlProperty p(object, name);
p.write(value);

Returns true on success, false otherwise.

[static] bool QQmlProperty::write(QObject *object, const QString &name, const QVariant &value, QQmlContext *ctxt)

Writes value to the name property of object using the context ctxt. This method is equivalent to:

QQmlProperty p(object, name, ctxt);
p.write(value);

Returns true on success, false otherwise.

[static] bool QQmlProperty::write(QObject *object, const QString &name, const QVariant &value, QQmlEngine *engine)

Writes value to the name property of object using the environment for instantiating QML components that is provided by engine. This method is equivalent to:

QQmlProperty p(object, name, engine);
p.write(value);

Returns true on success, false otherwise.

bool QQmlProperty::operator==(const QQmlProperty &other) const

Returns true if other and this QQmlProperty represent the same property.