QDeclarativeExpression Class Reference

The QDeclarativeExpression class evaluates JavaScript in a QML context. More...

#include <qdeclarativeexpression.h>

Inheritance diagram for QDeclarativeExpression:

Signals
void	valueChanged ()
	Emitted each time the expression value changes from the last time it was evaluated. More...
Signals inherited from QObject
void	destroyed (QObject *=0)
	This signal is emitted immediately before the object obj is destroyed, and can not be blocked. More...

Public Functions
void	clearError ()
	Clear any expression errors. More...
QDeclarativeContext *	context () const
	Returns the QDeclarativeContext this expression is associated with, or 0 if there is no association or the QDeclarativeContext has been destroyed. More...
QDeclarativeEngine *	engine () const
	Returns the QDeclarativeEngine this expression is associated with, or 0 if there is no association or the QDeclarativeEngine has been destroyed. More...
QDeclarativeError	error () const
	Return any error from the last call to evaluate(). More...
QVariant	evaluate (bool *valueIsUndefined=0)
	Evaulates the expression, returning the result of the evaluation, or an invalid QVariant if the expression is invalid or has an error. More...
QString	expression () const
	Returns the expression string. More...
bool	hasError () const
	Returns true if the last call to evaluate() resulted in an error, otherwise false. More...
int	lineNumber () const
	Returns the source file line number for this expression. More...
bool	notifyOnValueChanged () const
	Returns true if the valueChanged() signal is emitted when the expression's evaluated value changes. More...
	QDeclarativeExpression ()
	Create an invalid QDeclarativeExpression. More...
	QDeclarativeExpression (QDeclarativeContext *, QObject *, const QString &, QObject *=0)
	Create a QDeclarativeExpression object that is a child of parent. More...
QObject *	scopeObject () const
	Returns the expression's scope object, if provided, otherwise 0. More...
void	setExpression (const QString &)
	Set the expression to expression. More...
void	setNotifyOnValueChanged (bool)
	Sets whether the valueChanged() signal is emitted when the expression's evaluated value changes. More...
void	setSourceLocation (const QString &fileName, int line)
	Set the location of this expression to line of url. More...
QString	sourceFile () const
	Returns the source file URL for this expression. More...
virtual	~QDeclarativeExpression ()
	Destroy the QDeclarativeExpression instance. More...
Public Functions inherited from QObject
bool	blockSignals (bool b)
	If block is true, signals emitted by this object are blocked (i.e., emitting a signal will not invoke anything connected to it). More...
const QObjectList &	children () const
	Returns a list of child objects. More...
bool	connect (const QObject *sender, const char *signal, const char *member, Qt::ConnectionType type=Qt::AutoConnection) const
bool	disconnect (const char *signal=0, const QObject *receiver=0, const char *member=0)
bool	disconnect (const QObject *receiver, const char *member=0)
void	dumpObjectInfo ()
	Dumps information about signal connections, etc. More...
void	dumpObjectTree ()
	Dumps a tree of children to the debug output. More...
QList< QByteArray >	dynamicPropertyNames () const
	Returns the names of all properties that were dynamically added to the object using setProperty(). More...
virtual bool	event (QEvent *)
	This virtual function receives events to an object and should return true if the event e was recognized and processed. More...
virtual bool	eventFilter (QObject *, QEvent *)
	Filters events if this object has been installed as an event filter for the watched object. More...
template<typename T >
T	findChild (const QString &aName=QString()) const
	Returns the child of this object that can be cast into type T and that is called name, or 0 if there is no such object. More...
template<typename T >
QList< T >	findChildren (const QString &aName=QString()) const
	Returns all children of this object with the given name that can be cast to type T, or an empty list if there are no such objects. More...
template<typename T >
QList< T >	findChildren (const QRegExp &re) const
bool	inherits (const char *classname) const
	Returns true if this object is an instance of a class that inherits className or a QObject subclass that inherits className; otherwise returns false. More...
void	installEventFilter (QObject *)
	Installs an event filter filterObj on this object. More...
bool	isWidgetType () const
	Returns true if the object is a widget; otherwise returns false. More...
void	killTimer (int id)
	Kills the timer with timer identifier, id. More...
virtual const QMetaObject *	metaObject () const
	Returns a pointer to the meta-object of this object. More...
void	moveToThread (QThread *thread)
	Changes the thread affinity for this object and its children. More...
QString	objectName () const
QObject *	parent () const
	Returns a pointer to the parent object. More...
QVariant	property (const char *name) const
	Returns the value of the object's name property. More...
Q_INVOKABLE	QObject (QObject *parent=0)
	Constructs an object with parent object parent. More...
void	removeEventFilter (QObject *)
	Removes an event filter object obj from this object. More...
void	setObjectName (const QString &name)
void	setParent (QObject *)
	Makes the object a child of parent. More...
bool	setProperty (const char *name, const QVariant &value)
	Sets the value of the object's name property to value. More...
void	setUserData (uint id, QObjectUserData *data)
bool	signalsBlocked () const
	Returns true if signals are blocked; otherwise returns false. More...
int	startTimer (int interval)
	Starts a timer and returns a timer identifier, or returns zero if it could not start a timer. More...
QThread *	thread () const
	Returns the thread in which the object lives. More...
QObjectUserData *	userData (uint id) const
virtual	~QObject ()
	Destroys the object, deleting all its child objects. More...

Protected Functions
	QDeclarativeExpression (QDeclarativeContextData *, QObject *, const QString &, QDeclarativeExpressionPrivate &dd)
	QDeclarativeExpression (QDeclarativeContextData *, QObject *, const QScriptValue &, QDeclarativeExpressionPrivate &dd)
	QDeclarativeExpression (QDeclarativeContextData *, void *, QDeclarativeRefCount *rc, QObject *me, const QString &, int, QDeclarativeExpressionPrivate &dd)
Protected Functions inherited from QObject
virtual void	childEvent (QChildEvent *)
	This event handler can be reimplemented in a subclass to receive child events. More...
virtual void	connectNotify (const char *signal)
	This virtual function is called when something has been connected to signal in this object. More...
virtual void	customEvent (QEvent *)
	This event handler can be reimplemented in a subclass to receive custom events. More...
virtual void	disconnectNotify (const char *signal)
	This virtual function is called when something has been disconnected from signal in this object. More...
	QObject (QObjectPrivate &dd, QObject *parent=0)
int	receivers (const char *signal) const
	Returns the number of receivers connected to the signal. More...
QObject *	sender () const
	Returns a pointer to the object that sent the signal, if called in a slot activated by a signal; otherwise it returns 0. More...
int	senderSignalIndex () const
virtual void	timerEvent (QTimerEvent *)
	This event handler can be reimplemented in a subclass to receive timer events for the object. More...

Private Functions
	QDeclarativeExpression (QDeclarativeContextData *, QObject *, const QString &)

Friends
class	QDeclarativeContext
class	QDeclarativeDebugger
class	QDeclarativeVME

Additional Inherited Members
Public Slots inherited from QObject
void	deleteLater ()
	Schedules this object for deletion. More...
Static Public Functions inherited from QObject
static bool	connect (const QObject *sender, const char *signal, const QObject *receiver, const char *member, Qt::ConnectionType=Qt::AutoConnection)
	Creates a connection of the given type from the signal in the sender object to the method in the receiver object. More...
static bool	connect (const QObject *sender, const QMetaMethod &signal, const QObject *receiver, const QMetaMethod &method, Qt::ConnectionType type=Qt::AutoConnection)
static bool	disconnect (const QObject *sender, const char *signal, const QObject *receiver, const char *member)
	Disconnects signal in object sender from method in object receiver. More...
static bool	disconnect (const QObject *sender, const QMetaMethod &signal, const QObject *receiver, const QMetaMethod &member)
static uint	registerUserData ()
static QString	tr (const char *sourceText, const char *comment=0, int n=-1)
static QString	trUtf8 (const char *sourceText, const char *comment=0, int n=-1)
Static Public Variables inherited from QObject
static const QMetaObject	staticMetaObject
	This variable stores the meta-object for the class. More...
Protected Variables inherited from QObject
QScopedPointer< QObjectData >	d_ptr
Static Protected Variables inherited from QObject
static const QMetaObject	staticQtMetaObject
Related Functions inherited from QObject
T	qFindChildqFindChildren (const QObject *obj, const QString &name)()
QList< T >	qFindChildrenqFindChildren (const QObject *obj, const QString &name)()
QList< T >	qFindChildrenqFindChildren (const QObject *obj, const QRegExp &regExp)()
T *	qobject_cast (QObject *object)
	QObjectList
void *	qt_find_obj_child (QObject *parent, const char *type, const QString &name)
	Returns a pointer to the object named name that inherits type and with a given parent. More...

Detailed Description

The QDeclarativeExpression class evaluates JavaScript in a QML context.

Since

4.7

For example, given a file main.qml like this:

import QtQuick 1.0

Item {
    width: 200; height: 200
}

The following code evaluates a JavaScript expression in the context of the above QML:

QDeclarativeEngine *engine = new QDeclarativeEngine;
QDeclarativeComponent component(engine, QUrl::fromLocalFile("main.qml"));

QObject *myObject = component.create();
QDeclarativeExpression *expr = new QDeclarativeExpression(engine->rootContext(), myObject, "width * 2");
int result = expr->evaluate().toInt();  // result = 400

Definition at line 63 of file qdeclarativeexpression.h.

Constructors and Destructors

QDeclarativeExpression() [1/6]

QDeclarativeExpression::QDeclarativeExpression

(

)

Create an invalid QDeclarativeExpression.

As the expression will not have an associated QDeclarativeContext, this will be a null expression object and its value will always be an invalid QVariant.

Definition at line 249 of file qdeclarativeexpression.cpp.

: QObject(*new QDeclarativeExpressionPrivate, 0)
{
    Q_D(QDeclarativeExpression);

    if (QDeclarativeExpression_notifyIdx == -1) 
        QDeclarativeExpression_notifyIdx = QDeclarativeExpression::staticMetaObject.indexOfMethod("_q_notify()");
    d->setNotifyObject(this, QDeclarativeExpression_notifyIdx);
}

QDeclarativeExpression() [2/6]

QDeclarativeExpression::QDeclarativeExpression	(	QDeclarativeContext *	ctxt,
		QObject *	scope,
		const QString &	expression,
		QObject *	parent = 0
	)

Create a QDeclarativeExpression object that is a child of parent.

The expression JavaScript will be executed in the ctxt QDeclarativeContext. If specified, the scope object's properties will also be in scope during the expression's execution.

Definition at line 281 of file qdeclarativeexpression.cpp.

: QObject(*new QDeclarativeExpressionPrivate, parent)
{
    Q_D(QDeclarativeExpression);
    d->init(QDeclarativeContextData::get(ctxt), expression, scope);

    if (QDeclarativeExpression_notifyIdx == -1) 
        QDeclarativeExpression_notifyIdx = QDeclarativeExpression::staticMetaObject.indexOfMethod("_q_notify()");
    d->setNotifyObject(this, QDeclarativeExpression_notifyIdx);
}

~QDeclarativeExpression()

QDeclarativeExpression::~QDeclarativeExpression ( )

virtual

Destroy the QDeclarativeExpression instance.

Definition at line 339 of file qdeclarativeexpression.cpp.

{
}

QDeclarativeExpression() [3/6]

QDeclarativeExpression::QDeclarativeExpression ( QDeclarativeContextData *  ctxt, QObject *  scope, const QString &  expression, QDeclarativeExpressionPrivate &  dd  )

protected

Warning

This function is not part of the public interface.

Definition at line 311 of file qdeclarativeexpression.cpp.

: QObject(dd, 0)
{
    Q_D(QDeclarativeExpression);
    d->init(ctxt, expression, scope);

    if (QDeclarativeExpression_notifyIdx == -1) 
        QDeclarativeExpression_notifyIdx = QDeclarativeExpression::staticMetaObject.indexOfMethod("_q_notify()");
    d->setNotifyObject(this, QDeclarativeExpression_notifyIdx);
}

QDeclarativeExpression() [4/6]

QDeclarativeExpression::QDeclarativeExpression ( QDeclarativeContextData *  ctxt, QObject *  scope, const QScriptValue &  func, QDeclarativeExpressionPrivate &  dd  )

protected

Warning

This function is not part of the public interface.

Definition at line 324 of file qdeclarativeexpression.cpp.

: QObject(dd, 0)
{
    Q_D(QDeclarativeExpression);
    d->init(ctxt, func, scope);

    if (QDeclarativeExpression_notifyIdx == -1)
        QDeclarativeExpression_notifyIdx = QDeclarativeExpression::staticMetaObject.indexOfMethod("_q_notify()");
    d->setNotifyObject(this, QDeclarativeExpression_notifyIdx);
}

QDeclarativeExpression() [5/6]

QDeclarativeExpression::QDeclarativeExpression ( QDeclarativeContextData *  ctxt, void *  expr, QDeclarativeRefCount *  rc, QObject *  me, const QString &  url, int  lineNumber, QDeclarativeExpressionPrivate &  dd  )

protected

Warning

This function is not part of the public interface.

Definition at line 260 of file qdeclarativeexpression.cpp.

: QObject(dd, 0)
{
    Q_D(QDeclarativeExpression);
    d->init(ctxt, expr, rc, me, url, lineNumber);

    if (QDeclarativeExpression_notifyIdx == -1) 
        QDeclarativeExpression_notifyIdx = QDeclarativeExpression::staticMetaObject.indexOfMethod("_q_notify()");
    d->setNotifyObject(this, QDeclarativeExpression_notifyIdx);
}

QDeclarativeExpression() [6/6]

QDeclarativeExpression::QDeclarativeExpression ( QDeclarativeContextData *  ctxt, QObject *  scope, const QString &  expression  )

private

Warning

This function is not part of the public interface.

Definition at line 298 of file qdeclarativeexpression.cpp.

: QObject(*new QDeclarativeExpressionPrivate, 0)
{
    Q_D(QDeclarativeExpression);
    d->init(ctxt, expression, scope);

    if (QDeclarativeExpression_notifyIdx == -1) 
        QDeclarativeExpression_notifyIdx = QDeclarativeExpression::staticMetaObject.indexOfMethod("_q_notify()");
    d->setNotifyObject(this, QDeclarativeExpression_notifyIdx);
}

Functions

clearError()

void QDeclarativeExpression::clearError

(

)

Clear any expression errors.

Calls to hasError() following this will return false.

See also

hasError(), error()

Definition at line 781 of file qdeclarativeexpression.cpp.

{
    Q_D(QDeclarativeExpression);
    d->error = QDeclarativeError();
}

context()

QDeclarativeContext * QDeclarativeExpression::context

(

)

const

Returns the QDeclarativeContext this expression is associated with, or 0 if there is no association or the QDeclarativeContext has been destroyed.

Definition at line 357 of file qdeclarativeexpression.cpp.

Referenced by QDeclarativeQtScriptExpression::eval(), QDeclarativeQtScriptExpression::scriptValue(), QDeclarativeExpressionPrivate::scriptValue(), and QDeclarativeExpressionPrivate::value().

{
    Q_D(const QDeclarativeExpression);
    QDeclarativeContextData *data = d->context();
    return data?data->asQDeclarativeContext():0;
}

engine()

QDeclarativeEngine * QDeclarativeExpression::engine

(

)

const

Returns the QDeclarativeEngine this expression is associated with, or 0 if there is no association or the QDeclarativeEngine has been destroyed.

Definition at line 347 of file qdeclarativeexpression.cpp.

Referenced by QDeclarativeBinding::createBinding(), QDeclarativeQtScriptExpression::eval(), QDeclarativeBoundSignal::qt_metacall(), QDeclarativeQtScriptExpression::scriptValue(), and QDeclarativeExpressionPrivate::scriptValue().

{
    Q_D(const QDeclarativeExpression);
    return d->context()?d->context()->engine:0;
}

error()

QDeclarativeError QDeclarativeExpression::error

(

)

const

Return any error from the last call to evaluate().

If there was no error, this returns an invalid QDeclarativeError instance.

See also

hasError(), clearError()

Definition at line 794 of file qdeclarativeexpression.cpp.

Referenced by QDeclarativeQtScriptExpression::eval(), QDeclarativeGestureAreaPrivate::gestureEvent(), and QDeclarativeBoundSignal::qt_metacall().

{
    Q_D(const QDeclarativeExpression);
    return d->error;
}

evaluate()

QVariant QDeclarativeExpression::evaluate

(

bool *

valueIsUndefined = 0

)

Evaulates the expression, returning the result of the evaluation, or an invalid QVariant if the expression is invalid or has an error.

valueIsUndefined is set to true if the expression resulted in an undefined value.

See also

hasError(), error()

Definition at line 682 of file qdeclarativeexpression.cpp.

Referenced by QDeclarativePropertyChanges::changeExpression(), QDeclarativeGestureAreaPrivate::gestureEvent(), QDeclarativeEngineDebugService::messageReceived(), QDeclarativeWatchProxy::notifyValueChanged(), and QDeclarativeStateGroupPrivate::updateAutoState().

{
    Q_D(QDeclarativeExpression);
    return d->value(0, valueIsUndefined);
}

expression()

QString QDeclarativeExpression::expression

(

)

const

Returns the expression string.

Definition at line 367 of file qdeclarativeexpression.cpp.

Referenced by QDeclarativePropertyChanges::actions(), QDeclarativeEngineDebugService::buildObjectDump(), QDeclarativePropertyChanges::changeExpression(), QDeclarativeBinding::expression(), QDeclarativeBoundSignal::qt_metacall(), QDeclarativeExpressionPrivate::scriptValue(), setExpression(), and QDeclarativeQtScriptExpression::updateGuards().

{
    Q_D(const QDeclarativeExpression);
    return d->expression;
}

hasError()

bool QDeclarativeExpression::hasError

(

)

const

Returns true if the last call to evaluate() resulted in an error, otherwise false.

See also

error(), clearError()

Definition at line 769 of file qdeclarativeexpression.cpp.

Referenced by QDeclarativeGestureAreaPrivate::gestureEvent(), and QDeclarativeBoundSignal::qt_metacall().

{
    Q_D(const QDeclarativeExpression);
    return d->error.isValid();
}

lineNumber()

int QDeclarativeExpression::lineNumber

(

)

const

Returns the source file line number for this expression.

The source location must have been previously set by calling setSourceLocation().

Definition at line 734 of file qdeclarativeexpression.cpp.

Referenced by QDeclarativePropertyChanges::actions(), QDeclarativeBinding::createBinding(), QDeclarativeExpressionPrivate::exceptionToError(), QDeclarativeBindingProfiler::QDeclarativeBindingProfiler(), and QDeclarativeBoundSignal::qt_metacall().

{
    Q_D(const QDeclarativeExpression);
    return d->line;
}

notifyOnValueChanged()

bool QDeclarativeExpression::notifyOnValueChanged

(

)

const

Returns true if the valueChanged() signal is emitted when the expression's evaluated value changes.

Definition at line 692 of file qdeclarativeexpression.cpp.

{
    Q_D(const QDeclarativeExpression);
    return d->notifyOnValueChange();
}

scopeObject()

QObject * QDeclarativeExpression::scopeObject

(

)

const

Returns the expression's scope object, if provided, otherwise 0.

In addition to data provided by the expression's QDeclarativeContext, the scope object's properties are also in scope during the expression's evaluation.

Definition at line 757 of file qdeclarativeexpression.cpp.

Referenced by QDeclarativeEngineDebugService::buildObjectDump(), QDeclarativeQtScriptExpression::eval(), and QDeclarativeExpressionPrivate::scriptValue().

{
    Q_D(const QDeclarativeExpression);
    return d->scopeObject;
}

setExpression()

void QDeclarativeExpression::setExpression

(

const QString &

expression

)

Set the expression to expression.

Definition at line 376 of file qdeclarativeexpression.cpp.

{
    Q_D(QDeclarativeExpression);

    d->resetNotifyOnChange();
    d->expression = expression;
    d->expressionFunctionValid = false;
    d->expressionFunction = QScriptValue();
}

setNotifyOnValueChanged()

void QDeclarativeExpression::setNotifyOnValueChanged

(

bool

notifyOnChange

)

Sets whether the valueChanged() signal is emitted when the expression's evaluated value changes.

If notifyOnChange is true, the QDeclarativeExpression will monitor properties involved in the expression's evaluation, and emit QDeclarativeExpression::valueChanged() if they have changed. This allows an application to ensure that any value associated with the result of the expression remains up to date.

If notifyOnChange is false (default), the QDeclarativeExpression will not montitor properties involved in the expression's evaluation, and QDeclarativeExpression::valueChanged() will never be emitted. This is more efficient if an application wants a "one off" evaluation of the expression.

Definition at line 714 of file qdeclarativeexpression.cpp.

Referenced by QDeclarativeWatcher::addWatch(), QDeclarativeBinding::disconnect(), QDeclarativeBinding::QDeclarativeBinding(), QDeclarativeEngineDebugService::setBinding(), QDeclarativeBinding::setEnabled(), and QDeclarativeBoundSignal::setExpression().

{
    Q_D(QDeclarativeExpression);
    d->setNotifyOnValueChange(notifyOnChange);
}

setSourceLocation()

void QDeclarativeExpression::setSourceLocation	(	const QString &	url,
		int	line
	)

Set the location of this expression to line of url.

This information is used by the script engine.

Definition at line 744 of file qdeclarativeexpression.cpp.

Referenced by QDeclarativePropertyChanges::actions(), QDeclarativePropertyChangesPrivate::decode(), QDeclarativeEngineDebugService::setBinding(), QDeclarativeValueTypeScriptClass::setProperty(), and QDeclarativeObjectScriptClass::setProperty().

{
    Q_D(QDeclarativeExpression);
    d->url = url;
    d->line = line;
}

sourceFile()

QString QDeclarativeExpression::sourceFile

(

)

const

Returns the source file URL for this expression.

The source location must have been previously set by calling setSourceLocation().

Definition at line 724 of file qdeclarativeexpression.cpp.

Referenced by QDeclarativePropertyChanges::actions(), QDeclarativeBindingProfiler::QDeclarativeBindingProfiler(), and QDeclarativeBoundSignal::qt_metacall().

{
    Q_D(const QDeclarativeExpression);
    return d->url;
}

valueChanged

void QDeclarativeExpression::valueChanged ( )

signal

Emitted each time the expression value changes from the last time it was evaluated.

The expression must have been evaluated at least once (by calling QDeclarativeExpression::evaluate()) before this signal will be emitted.

Friends and Related Functions

QDeclarativeContext

friend class QDeclarativeContext

friend

Definition at line 110 of file qdeclarativeexpression.h.

QDeclarativeDebugger

friend class QDeclarativeDebugger

friend

Definition at line 109 of file qdeclarativeexpression.h.

QDeclarativeVME

friend class QDeclarativeVME

friend

Definition at line 111 of file qdeclarativeexpression.h.

---

The documentation for this class was generated from the following files:

• /src/declarative/qml/qdeclarativeexpression.h
• /src/declarative/qml/qdeclarativeexpression.cpp