Qt 4.8: QDeclarativeProperty Class Reference

Qt Reference Documentation

# QDeclarativeProperty Class Reference

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

     #include <QDeclarativeProperty>

This class was introduced in Qt 4.7.

- List of all members, including inherited members

## Public Types

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

## Public Functions

| QDeclarativeProperty ()
| QDeclarativeProperty ( QObject * obj )
| QDeclarativeProperty ( QObject * obj, QDeclarativeContext * ctxt )
| QDeclarativeProperty ( QObject * obj, QDeclarativeEngine * engine )
| QDeclarativeProperty ( QObject * obj, const QString & name )
| QDeclarativeProperty ( QObject * obj, const QString & name, QDeclarativeContext * ctxt )
| QDeclarativeProperty ( QObject * obj, const QString & name, QDeclarativeEngine * engine )
| QDeclarativeProperty ( const QDeclarativeProperty & 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
int | propertyType () const
PropertyTypeCategory | propertyTypeCategory () const
const char * | propertyTypeName () const
QVariant | read () const
bool | reset () const
Type | type () const
bool | write ( const QVariant & value ) const
QDeclarativeProperty & | operator= ( const QDeclarativeProperty & other )
bool | operator== ( const QDeclarativeProperty & other ) const

## Static Public Members

QVariant | read ( QObject * object, const QString & name )
QVariant | read ( QObject * object, const QString & name, QDeclarativeContext * ctxt )
QVariant | read ( QObject * object, const QString & name, QDeclarativeEngine * engine )
bool | write ( QObject * object, const QString & name, const QVariant & value )
bool | write ( QObject * object, const QString & name, const QVariant & value, QDeclarativeContext * ctxt )
bool | write ( QObject * object, const QString & name, const QVariant & value, QDeclarativeEngine * engine )

## Detailed Description

The QDeclarativeProperty class abstracts accessing properties on objects created from QML.

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 QDeclarativeProperty class that simplifies some of their natural complexity.

Unlike QMetaProperty which represents a property on a class type, QDeclarativeProperty encapsulates a property on a specific object instance. To read a property's value, programmers create a QDeclarativeProperty 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 1.0

     Text { text: "A bit of text" }

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

     #include <QDeclarativeProperty>
     #include <QGraphicsObject>

     ...

     QDeclarativeView view(QUrl::fromLocalFile("MyItem.qml"));
     QDeclarativeProperty 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 QDeclarativeProperty::PropertyTypeCategory

This enum specifies a category of QML property.

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

### enum QDeclarativeProperty::Type

This enum specifies a type of QML property.

Constant | Value | Description
--- | --- | ---
`QDeclarativeProperty::Invalid` | `0` | The property is invalid.
`QDeclarativeProperty::Property` | `1` | The property is a regular Qt property.
`QDeclarativeProperty::SignalProperty` | `2` | The property is a signal property.

## Member Function Documentation

### QDeclarativeProperty::QDeclarativeProperty ()

Create an invalid QDeclarativeProperty.

### QDeclarativeProperty::QDeclarativeProperty ( QObject * obj )

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

### QDeclarativeProperty::QDeclarativeProperty ( QObject * obj, QDeclarativeContext * ctxt )

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

### QDeclarativeProperty::QDeclarativeProperty ( QObject * obj, QDeclarativeEngine * engine )

Creates a QDeclarativeProperty 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 QDeclarativeProperty will be created.

### QDeclarativeProperty::QDeclarativeProperty ( QObject * obj, const QString & name )

Creates a QDeclarativeProperty for the property name of obj.

### QDeclarativeProperty::QDeclarativeProperty ( QObject * obj, const QString & name, QDeclarativeContext * ctxt )

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

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

### QDeclarativeProperty::QDeclarativeProperty ( QObject * obj, const QString & name, QDeclarativeEngine * engine )

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

### QDeclarativeProperty::QDeclarativeProperty ( const QDeclarativeProperty & other )

Create a copy of other.

### bool QDeclarativeProperty::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 QDeclarativeProperty::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 QDeclarativeProperty::hasNotifySignal () const

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

### int QDeclarativeProperty::index () const

Return the Qt metaobject index of the property.

### bool QDeclarativeProperty::isDesignable () const

Returns true if the property is designable, otherwise false.

### bool QDeclarativeProperty::isProperty () const

Returns true if this QDeclarativeProperty represents a regular Qt property.

### bool QDeclarativeProperty::isResettable () const

Returns true if the property is resettable, otherwise false.

### bool QDeclarativeProperty::isSignalProperty () const

Returns true if this QDeclarativeProperty represents a QML signal property.

### bool QDeclarativeProperty::isValid () const

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

### bool QDeclarativeProperty::isWritable () const

Returns true if the property is writable, otherwise false.

### QMetaMethod QDeclarativeProperty::method () const

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

### QString QDeclarativeProperty::name () const

Return the name of this QML property.

### bool QDeclarativeProperty::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 * QDeclarativeProperty::object () const

Returns the QDeclarativeProperty's QObject.

### QMetaProperty QDeclarativeProperty::property () const

Returns the Qt property associated with this QML property.

### int QDeclarativeProperty::propertyType () const

Returns the QVariant type of the property, or QVariant::Invalid if the property has no QVariant type.

### PropertyTypeCategory QDeclarativeProperty::propertyTypeCategory () const

Returns the property category.

### const char * QDeclarativeProperty::propertyTypeName () const

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

### QVariant QDeclarativeProperty::read () const

Returns the property value.

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

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

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

### QVariant QDeclarativeProperty::read ( QObject * object, const QString & name, QDeclarativeContext * ctxt )`[static]`

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

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

### QVariant QDeclarativeProperty::read ( QObject * object, const QString & name, QDeclarativeEngine * engine )`[static]`

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

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

### bool QDeclarativeProperty::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.

### Type QDeclarativeProperty::type () const

Returns the type of the property.

### bool QDeclarativeProperty::write ( const QVariant & value ) const

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

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

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

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

### bool QDeclarativeProperty::write ( QObject * object, const QString & name, const QVariant & value, QDeclarativeContext * ctxt )`[static]`

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

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

### bool QDeclarativeProperty::write ( QObject * object, const QString & name, const QVariant & value, QDeclarativeEngine * engine )`[static]`

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:

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

### QDeclarativeProperty & QDeclarativeProperty::operator= ( const QDeclarativeProperty & other )

Assign other to this QDeclarativeProperty.

### bool QDeclarativeProperty::operator== ( const QDeclarativeProperty & other ) const

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