qt-everywhere-src-5.14.1/qtdeclarative/src/qml/types/qqmlbind.cpp - orbit - Git at Google

 /****************************************************************************
 **
 ** Copyright (C) 2016 The Qt Company Ltd.
 ** Contact: https://www.qt.io/licensing/
 **
 ** This file is part of the QtQml module of the Qt Toolkit.
 **
 ** $QT_BEGIN_LICENSE:LGPL$
 ** Commercial License Usage
 ** Licensees holding valid commercial Qt licenses may use this file in
 ** accordance with the commercial license agreement provided with the
 ** Software or, alternatively, in accordance with the terms contained in
 ** a written agreement between you and The Qt Company. For licensing terms
 ** and conditions see https://www.qt.io/terms-conditions. For further
 ** information use the contact form at https://www.qt.io/contact-us.
 **
 ** GNU Lesser General Public License Usage
 ** Alternatively, this file may be used under the terms of the GNU Lesser
 ** General Public License version 3 as published by the Free Software
 ** Foundation and appearing in the file LICENSE.LGPL3 included in the
 ** packaging of this file. Please review the following information to
 ** ensure the GNU Lesser General Public License version 3 requirements
 ** will be met: https://www.gnu.org/licenses/lgpl-3.0.html.
 **
 ** GNU General Public License Usage
 ** Alternatively, this file may be used under the terms of the GNU
 ** General Public License version 2.0 or (at your option) the GNU General
 ** Public license version 3 or any later version approved by the KDE Free
 ** Qt Foundation. The licenses are as published by the Free Software
 ** Foundation and appearing in the file LICENSE.GPL2 and LICENSE.GPL3
 ** included in the packaging of this file. Please review the following
 ** information to ensure the GNU General Public License requirements will
 ** be met: https://www.gnu.org/licenses/gpl-2.0.html and
 ** https://www.gnu.org/licenses/gpl-3.0.html.
 **
 ** $QT_END_LICENSE$
 **
 ****************************************************************************/

 #include "qqmlbind_p.h"

 #include <private/qqmlnullablevalue_p.h>
 #include <private/qqmlproperty_p.h>
 #include <private/qqmlbinding_p.h>
 #include <private/qqmlmetatype_p.h>
 #include <private/qqmlvmemetaobject_p.h>
 #include <private/qv4persistent_p.h>

 #include <qqmlengine.h>
 #include <qqmlcontext.h>
 #include <qqmlproperty.h>
 #include <qqmlinfo.h>

 #include <QtCore/qfile.h>
 #include <QtCore/qdebug.h>
 #include <QtCore/qtimer.h>
 #include <QtCore/qloggingcategory.h>

 #include <private/qobject_p.h>

 QT_BEGIN_NAMESPACE

 Q_DECLARE_LOGGING_CATEGORY(lcBindingRemoval)

 class QQmlBindPrivate : public QObjectPrivate
 {
 public:
     QQmlBindPrivate()
         : obj(nullptr)
         , prevBind(QQmlAbstractBinding::Ptr())
         , prevIsVariant(false)
         , componentComplete(true)
         , delayed(false)
         , pendingEval(false)
         , restoreBinding(true)
         , restoreValue(false)
         , restoreModeExplicit(false)
         , writingProperty(false)
     {}
     ~QQmlBindPrivate() { }

     QQmlNullableValue<bool> when;
     QPointer<QObject> obj;
     QString propName;
     QQmlNullableValue<QJSValue> value;
     QQmlProperty prop;
     QQmlAbstractBinding::Ptr prevBind;
     QV4::PersistentValue v4Value;
     QVariant prevValue;
     bool prevIsVariant:1;
     bool componentComplete:1;
     bool delayed:1;
     bool pendingEval:1;
     bool restoreBinding:1;
     bool restoreValue:1;
     bool restoreModeExplicit:1;
     bool writingProperty: 1;

     void validate(QObject *binding) const;
     void clearPrev();
 };

 void QQmlBindPrivate::validate(QObject *binding) const
 {
     if (!obj || (when.isValid() && !when))
         return;

     if (!prop.isValid()) {
         qmlWarning(binding) << "Property '" << propName << "' does not exist on " << QQmlMetaType::prettyTypeName(obj) << ".";
         return;
     }

     if (!prop.isWritable()) {
         qmlWarning(binding) << "Property '" << propName << "' on " << QQmlMetaType::prettyTypeName(obj) << " is read-only.";
         return;
     }
 }

 /*!
     \qmltype Binding
     \instantiates QQmlBind
     \inqmlmodule QtQml
     \ingroup qtquick-interceptors
     \brief Enables the arbitrary creation of property bindings.

     In QML, property bindings result in a dependency between the properties of
     different objects.

     \section1 Binding to an Inaccessible Property

     Sometimes it is necessary to bind an object's property to
     that of another object that isn't directly instantiated by QML, such as a
     property of a class exported to QML by C++. You can use the Binding type
     to establish this dependency; binding any value to any object's property.

     For example, in a C++ application that maps an "app.enteredText" property
     into QML, you can use Binding to update the enteredText property.

     \code
     TextEdit { id: myTextField; text: "Please type here..." }
     Binding { target: app; property: "enteredText"; value: myTextField.text }
     \endcode

     When \c{text} changes, the C++ property \c{enteredText} will update
     automatically.

     \section1 Conditional Bindings

     In some cases you may want to modify the value of a property when a certain
     condition is met but leave it unmodified otherwise. Often, it's not possible
     to do this with direct bindings, as you have to supply values for all
     possible branches.

     For example, the code snippet below results in a warning whenever you
     release the mouse. This is because the value of the binding is undefined
     when the mouse isn't pressed.

     \qml
     // produces warning: "Unable to assign [undefined] to double value"
     value: if (mouse.pressed) mouse.mouseX
     \endqml

     The Binding type can prevent this warning.

     \qml
     Binding on value {
         when: mouse.pressed
         value: mouse.mouseX
     }
     \endqml

     The Binding type restores any previously set direct bindings on the
     property.

     \sa {Qt QML}
 */
 QQmlBind::QQmlBind(QObject *parent)
     : QObject(*(new QQmlBindPrivate), parent)
 {
 }

 QQmlBind::~QQmlBind()
 {
 }

 /*!
     \qmlproperty bool QtQml::Binding::when

     This property holds when the binding is active.
     This should be set to an expression that evaluates to true when you want the binding to be active.

     \code
     Binding {
         target: contactName; property: 'text'
         value: name; when: list.ListView.isCurrentItem
     }
     \endcode

     When the binding becomes inactive again, any direct bindings that were previously
     set on the property will be restored.

     \note By default, a previously set literal value is not restored when the Binding becomes
     inactive. Rather, the last value set by the now inactive Binding is retained. You can customize
     the restoration behavior for literal values as well as bindings using the \l restoreMode
     property. The default will change in Qt 6.0.

     \sa restoreMode
 */
 bool QQmlBind::when() const
 {
     Q_D(const QQmlBind);
     return d->when;
 }

 void QQmlBind::setWhen(bool v)
 {
     Q_D(QQmlBind);
     if (!d->when.isNull && d->when == v)
         return;

     d->when = v;
     if (v && d->componentComplete)
         d->validate(this);
     eval();
 }

 /*!
     \qmlproperty Object QtQml::Binding::target

     The object to be updated.
 */
 QObject *QQmlBind::object()
 {
     Q_D(const QQmlBind);
     return d->obj;
 }

 void QQmlBind::setObject(QObject *obj)
 {
     Q_D(QQmlBind);
     if (d->obj && d->when.isValid() && d->when) {
         /* if we switch the object at runtime, we need to restore the
            previous binding on the old object before continuing */
         d->when = false;
         eval();
         d->when = true;
     }
     d->obj = obj;
     if (d->componentComplete) {
         setTarget(QQmlProperty(d->obj, d->propName, qmlContext(this)));
         d->validate(this);
     }
     eval();
 }

 /*!
     \qmlproperty string QtQml::Binding::property

     The property to be updated.

     This can be a group property if the expression results in accessing a
     property of a \l {QML Basic Types}{value type}. For example:

     \qml
     Item {
         id: item

         property rect rectangle: Qt.rect(0, 0, 200, 200)
     }

     Binding {
         target: item
         property: "rectangle.x"
         value: 100
     }
     \endqml
 */
 QString QQmlBind::property() const
 {
     Q_D(const QQmlBind);
     return d->propName;
 }

 void QQmlBind::setProperty(const QString &p)
 {
     Q_D(QQmlBind);
     if (!d->propName.isEmpty() && d->when.isValid() && d->when) {
         /* if we switch the property name at runtime, we need to restore the
            previous binding on the old object before continuing */
         d->when = false;
         eval();
         d->when = true;
     }
     d->propName = p;
     if (d->componentComplete) {
         setTarget(QQmlProperty(d->obj, d->propName, qmlContext(this)));
         d->validate(this);
     }
     eval();
 }

 /*!
     \qmlproperty any QtQml::Binding::value

     The value to be set on the target object and property.  This can be a
     constant (which isn't very useful), or a bound expression.
 */
 QJSValue QQmlBind::value() const
 {
     Q_D(const QQmlBind);
     return d->value.value;
 }

 void QQmlBind::setValue(const QJSValue &v)
 {
     Q_D(QQmlBind);
     d->value = v;
     prepareEval();
 }

 /*!
     \qmlproperty bool QtQml::Binding::delayed
     \since 5.8

     This property holds whether the binding should be delayed.

     A delayed binding will not immediately update the target, but rather wait
     until the event queue has been cleared. This can be used as an optimization,
     or to prevent intermediary values from being assigned.

     \code
     Binding {
         target: contactName; property: 'text'
         value: givenName + " " + familyName; when: list.ListView.isCurrentItem
         delayed: true
     }
     \endcode
 */
 bool QQmlBind::delayed() const
 {
     Q_D(const QQmlBind);
     return d->delayed;
 }

 void QQmlBind::setDelayed(bool delayed)
 {
     Q_D(QQmlBind);
     if (d->delayed == delayed)
         return;

     d->delayed = delayed;

     if (!d->delayed)
         eval();
 }

 /*!
     \qmlproperty enumeration QtQml::Binding::restoreMode
     \since 5.14

     This property can be used to describe if and how the original value should
     be restored when the binding is disabled.

     The possible values are:
     \list
     \li Binding.RestoreNone The original value is not restored at all
     \li Binding.RestoreBinding The original value is restored if it was another
         binding. In that case the old binding is in effect again.
     \li Binding.RestoreValue The original value is restored if it was a plain
         value rather than a binding.
     \li Binding.RestoreBindingOrValue The original value is always restored.
     \endlist

     \warning The default value is Binding.RestoreBinding. This will change in
     Qt 6.0 to Binding.RestoreBindingOrValue.

     If you rely on any specific behavior regarding the restoration of plain
     values when bindings get disabled you should migrate to explicitly set the
     restoreMode.

     Reliance on a restoreMode that doesn't restore the previous binding or value
     for a specific property results in a run-time warning.
 */
 QQmlBind::RestorationMode QQmlBind::restoreMode() const
 {
     Q_D(const QQmlBind);
     unsigned result = RestoreNone;
     if (d->restoreValue)
         result |= RestoreValue;
     if (d->restoreBinding)
         result |= RestoreBinding;
     return RestorationMode(result);
 }

 void QQmlBind::setRestoreMode(RestorationMode newMode)
 {
     Q_D(QQmlBind);
     d->restoreModeExplicit = true;
     if (newMode != restoreMode()) {
         d->restoreValue = (newMode & RestoreValue);
         d->restoreBinding = (newMode & RestoreBinding);
         emit restoreModeChanged();
     }
 }

 void QQmlBind::setTarget(const QQmlProperty &p)
 {
     Q_D(QQmlBind);

     if (Q_UNLIKELY(lcBindingRemoval().isInfoEnabled())) {
         if (QObject *oldObject = d->prop.object()) {
             QMetaProperty prop = oldObject->metaObject()->property(d->prop.index());
             if (prop.hasNotifySignal()) {
                 QByteArray signal('2' + prop.notifySignal().methodSignature());
                 QObject::disconnect(oldObject, signal.constData(),
                                     this, SLOT(targetValueChanged()));
             }
         }
         p.connectNotifySignal(this, SLOT(targetValueChanged()));
     }

     d->prop = p;
 }

 void QQmlBind::classBegin()
 {
     Q_D(QQmlBind);
     d->componentComplete = false;
 }

 void QQmlBind::componentComplete()
 {
     Q_D(QQmlBind);
     d->componentComplete = true;
     if (!d->prop.isValid()) {
         setTarget(QQmlProperty(d->obj, d->propName, qmlContext(this)));
         d->validate(this);
     }
     eval();
 }

 void QQmlBind::prepareEval()
 {
     Q_D(QQmlBind);
     if (d->delayed) {
         if (!d->pendingEval)
             QTimer::singleShot(0, this, &QQmlBind::eval);
         d->pendingEval = true;
     } else {
         eval();
     }
 }

 void QQmlBindPrivate::clearPrev()
 {
     prevBind = nullptr;
     v4Value.clear();
     prevValue.clear();
     prevIsVariant = false;
 }

 void QQmlBind::eval()
 {
     Q_D(QQmlBind);
     d->pendingEval = false;
     if (!d->prop.isValid() || d->value.isNull || !d->componentComplete)
         return;

     if (d->when.isValid()) {
         if (!d->when) {
             //restore any previous binding
             if (d->prevBind) {
                 if (d->restoreBinding) {
                     QQmlAbstractBinding::Ptr p = d->prevBind;
                     d->clearPrev(); // Do that before setBinding(), as setBinding() may recurse.
                     QQmlPropertyPrivate::setBinding(p.data());
                 }
             } else if (!d->v4Value.isEmpty()) {
                 if (d->restoreValue) {
                     auto propPriv = QQmlPropertyPrivate::get(d->prop);
                     QQmlVMEMetaObject *vmemo = QQmlVMEMetaObject::get(propPriv->object);
                     Q_ASSERT(vmemo);
                     vmemo->setVMEProperty(propPriv->core.coreIndex(), *d->v4Value.valueRef());
                     d->clearPrev();
                 } else if (!d->restoreModeExplicit) {
                     qmlWarning(this)
                             << "Not restoring previous value because restoreMode has not been set."
                             << "This behavior is deprecated."
                             << "In Qt < 6.0 the default is Binding.RestoreBinding."
                             << "In Qt >= 6.0 the default is Binding.RestoreBindingOrValue.";
                 }
             } else if (d->prevIsVariant) {
                 if (d->restoreValue) {
                     d->prop.write(d->prevValue);
                     d->clearPrev();
                 } else if (!d->restoreModeExplicit) {
                     qmlWarning(this)
                             << "Not restoring previous value because restoreMode has not been set."
                             << "This behavior is deprecated."
                             << "In Qt < 6.0 the default is Binding.RestoreBinding."
                             << "In Qt >= 6.0 the default is Binding.RestoreBindingOrValue.";
                 }
             }
             return;
         }

         //save any set binding for restoration
         if (!d->prevBind && d->v4Value.isEmpty() && !d->prevIsVariant) {
             // try binding first
             d->prevBind = QQmlPropertyPrivate::binding(d->prop);

             if (!d->prevBind) { // nope, try a V4 value next
                 auto propPriv = QQmlPropertyPrivate::get(d->prop);
                 auto propData = propPriv->core;
                 if (!propPriv->valueTypeData.isValid() && propData.isVarProperty()) {
                     QQmlVMEMetaObject *vmemo = QQmlVMEMetaObject::get(propPriv->object);
                     Q_ASSERT(vmemo);
                     auto retVal = vmemo->vmeProperty(propData.coreIndex());
                     d->v4Value = QV4::PersistentValue(vmemo->engine, retVal);
                 } else { // nope, use the meta object to get a QVariant
                     d->prevValue = d->prop.read();
                     d->prevIsVariant = true;
                 }
             }
         }

         QQmlPropertyPrivate::removeBinding(d->prop);
     }

     d->writingProperty = true;
     d->prop.write(d->value.value.toVariant());
     d->writingProperty = false;
 }

 void QQmlBind::targetValueChanged()
 {
     Q_D(QQmlBind);
     if (d->writingProperty)
         return;

     if (d->when.isValid() && !d->when)
         return;

     QUrl url;
     quint16 line = 0;

     const QQmlData *ddata = QQmlData::get(this, false);
     if (ddata && ddata->outerContext) {
         url = ddata->outerContext->url();
         line = ddata->lineNumber;
     }

     qCInfo(lcBindingRemoval,
            "The target property of the Binding element created at %s:%d was changed from "
            "elsewhere. This does not overwrite the binding. The target property will still be "
            "updated when the value of the Binding element changes.",
            qPrintable(url.toString()), line);
 }

 QT_END_NAMESPACE

 #include "moc_qqmlbind_p.cpp"
	/****************************************************************************
	**
	** Copyright (C) 2016 The Qt Company Ltd.
	** Contact: https://www.qt.io/licensing/
	**
	** This file is part of the QtQml module of the Qt Toolkit.
	**
	** $QT_BEGIN_LICENSE:LGPL$
	** Commercial License Usage
	** Licensees holding valid commercial Qt licenses may use this file in
	** accordance with the commercial license agreement provided with the
	** Software or, alternatively, in accordance with the terms contained in
	** a written agreement between you and The Qt Company. For licensing terms
	** and conditions see https://www.qt.io/terms-conditions. For further
	** information use the contact form at https://www.qt.io/contact-us.
	**
	** GNU Lesser General Public License Usage
	** Alternatively, this file may be used under the terms of the GNU Lesser
	** General Public License version 3 as published by the Free Software
	** Foundation and appearing in the file LICENSE.LGPL3 included in the
	** packaging of this file. Please review the following information to
	** ensure the GNU Lesser General Public License version 3 requirements
	** will be met: https://www.gnu.org/licenses/lgpl-3.0.html.
	**
	** GNU General Public License Usage
	** Alternatively, this file may be used under the terms of the GNU
	** General Public License version 2.0 or (at your option) the GNU General
	** Public license version 3 or any later version approved by the KDE Free
	** Qt Foundation. The licenses are as published by the Free Software
	** Foundation and appearing in the file LICENSE.GPL2 and LICENSE.GPL3
	** included in the packaging of this file. Please review the following
	** information to ensure the GNU General Public License requirements will
	** be met: https://www.gnu.org/licenses/gpl-2.0.html and
	** https://www.gnu.org/licenses/gpl-3.0.html.
	**
	** $QT_END_LICENSE$
	**
	****************************************************************************/

	#include "qqmlbind_p.h"

	#include <private/qqmlnullablevalue_p.h>
	#include <private/qqmlproperty_p.h>
	#include <private/qqmlbinding_p.h>
	#include <private/qqmlmetatype_p.h>
	#include <private/qqmlvmemetaobject_p.h>
	#include <private/qv4persistent_p.h>

	#include <qqmlengine.h>
	#include <qqmlcontext.h>
	#include <qqmlproperty.h>
	#include <qqmlinfo.h>

	#include <QtCore/qfile.h>
	#include <QtCore/qdebug.h>
	#include <QtCore/qtimer.h>
	#include <QtCore/qloggingcategory.h>

	#include <private/qobject_p.h>

	QT_BEGIN_NAMESPACE

	Q_DECLARE_LOGGING_CATEGORY(lcBindingRemoval)

	class QQmlBindPrivate : public QObjectPrivate
	{
	public:
	QQmlBindPrivate()
	: obj(nullptr)
	, prevBind(QQmlAbstractBinding::Ptr())
	, prevIsVariant(false)
	, componentComplete(true)
	, delayed(false)
	, pendingEval(false)
	, restoreBinding(true)
	, restoreValue(false)
	, restoreModeExplicit(false)
	, writingProperty(false)
	{}
	~QQmlBindPrivate() { }

	QQmlNullableValue<bool> when;
	QPointer<QObject> obj;
	QString propName;
	QQmlNullableValue<QJSValue> value;
	QQmlProperty prop;
	QQmlAbstractBinding::Ptr prevBind;
	QV4::PersistentValue v4Value;
	QVariant prevValue;
	bool prevIsVariant:1;
	bool componentComplete:1;
	bool delayed:1;
	bool pendingEval:1;
	bool restoreBinding:1;
	bool restoreValue:1;
	bool restoreModeExplicit:1;
	bool writingProperty: 1;

	void validate(QObject *binding) const;
	void clearPrev();
	};

	void QQmlBindPrivate::validate(QObject *binding) const
	{
	if (!obj \|\| (when.isValid() && !when))
	return;

	if (!prop.isValid()) {
	qmlWarning(binding) << "Property '" << propName << "' does not exist on " << QQmlMetaType::prettyTypeName(obj) << ".";
	return;
	}

	if (!prop.isWritable()) {
	qmlWarning(binding) << "Property '" << propName << "' on " << QQmlMetaType::prettyTypeName(obj) << " is read-only.";
	return;
	}
	}

	/*!
	\qmltype Binding
	\instantiates QQmlBind
	\inqmlmodule QtQml
	\ingroup qtquick-interceptors
	\brief Enables the arbitrary creation of property bindings.

	In QML, property bindings result in a dependency between the properties of
	different objects.

	\section1 Binding to an Inaccessible Property

	Sometimes it is necessary to bind an object's property to
	that of another object that isn't directly instantiated by QML, such as a
	property of a class exported to QML by C++. You can use the Binding type
	to establish this dependency; binding any value to any object's property.

	For example, in a C++ application that maps an "app.enteredText" property
	into QML, you can use Binding to update the enteredText property.

	\code
	TextEdit { id: myTextField; text: "Please type here..." }
	Binding { target: app; property: "enteredText"; value: myTextField.text }
	\endcode

	When \c{text} changes, the C++ property \c{enteredText} will update
	automatically.

	\section1 Conditional Bindings

	In some cases you may want to modify the value of a property when a certain
	condition is met but leave it unmodified otherwise. Often, it's not possible
	to do this with direct bindings, as you have to supply values for all
	possible branches.

	For example, the code snippet below results in a warning whenever you
	release the mouse. This is because the value of the binding is undefined
	when the mouse isn't pressed.

	\qml
	// produces warning: "Unable to assign [undefined] to double value"
	value: if (mouse.pressed) mouse.mouseX
	\endqml

	The Binding type can prevent this warning.

	\qml
	Binding on value {
	when: mouse.pressed
	value: mouse.mouseX
	}
	\endqml

	The Binding type restores any previously set direct bindings on the
	property.

	\sa {Qt QML}
	*/
	QQmlBind::QQmlBind(QObject *parent)
	: QObject(*(new QQmlBindPrivate), parent)
	{
	}

	QQmlBind::~QQmlBind()
	{
	}

	/*!
	\qmlproperty bool QtQml::Binding::when

	This property holds when the binding is active.
	This should be set to an expression that evaluates to true when you want the binding to be active.

	\code
	Binding {
	target: contactName; property: 'text'
	value: name; when: list.ListView.isCurrentItem
	}
	\endcode

	When the binding becomes inactive again, any direct bindings that were previously
	set on the property will be restored.

	\note By default, a previously set literal value is not restored when the Binding becomes
	inactive. Rather, the last value set by the now inactive Binding is retained. You can customize
	the restoration behavior for literal values as well as bindings using the \l restoreMode
	property. The default will change in Qt 6.0.

	\sa restoreMode
	*/
	bool QQmlBind::when() const
	{
	Q_D(const QQmlBind);
	return d->when;
	}

	void QQmlBind::setWhen(bool v)
	{
	Q_D(QQmlBind);
	if (!d->when.isNull && d->when == v)
	return;

	d->when = v;
	if (v && d->componentComplete)
	d->validate(this);
	eval();
	}

	/*!
	\qmlproperty Object QtQml::Binding::target

	The object to be updated.
	*/
	QObject *QQmlBind::object()
	{
	Q_D(const QQmlBind);
	return d->obj;
	}

	void QQmlBind::setObject(QObject *obj)
	{
	Q_D(QQmlBind);
	if (d->obj && d->when.isValid() && d->when) {
	/* if we switch the object at runtime, we need to restore the
	previous binding on the old object before continuing */
	d->when = false;
	eval();
	d->when = true;
	}
	d->obj = obj;
	if (d->componentComplete) {
	setTarget(QQmlProperty(d->obj, d->propName, qmlContext(this)));
	d->validate(this);
	}
	eval();
	}

	/*!
	\qmlproperty string QtQml::Binding::property

	The property to be updated.

	This can be a group property if the expression results in accessing a
	property of a \l {QML Basic Types}{value type}. For example:

	\qml
	Item {
	id: item

	property rect rectangle: Qt.rect(0, 0, 200, 200)
	}

	Binding {
	target: item
	property: "rectangle.x"
	value: 100
	}
	\endqml
	*/
	QString QQmlBind::property() const
	{
	Q_D(const QQmlBind);
	return d->propName;
	}

	void QQmlBind::setProperty(const QString &p)
	{
	Q_D(QQmlBind);
	if (!d->propName.isEmpty() && d->when.isValid() && d->when) {
	/* if we switch the property name at runtime, we need to restore the
	previous binding on the old object before continuing */
	d->when = false;
	eval();
	d->when = true;
	}
	d->propName = p;
	if (d->componentComplete) {
	setTarget(QQmlProperty(d->obj, d->propName, qmlContext(this)));
	d->validate(this);
	}
	eval();
	}

	/*!
	\qmlproperty any QtQml::Binding::value

	The value to be set on the target object and property. This can be a
	constant (which isn't very useful), or a bound expression.
	*/
	QJSValue QQmlBind::value() const
	{
	Q_D(const QQmlBind);
	return d->value.value;
	}

	void QQmlBind::setValue(const QJSValue &v)
	{
	Q_D(QQmlBind);
	d->value = v;
	prepareEval();
	}

	/*!
	\qmlproperty bool QtQml::Binding::delayed
	\since 5.8

	This property holds whether the binding should be delayed.

	A delayed binding will not immediately update the target, but rather wait
	until the event queue has been cleared. This can be used as an optimization,
	or to prevent intermediary values from being assigned.

	\code
	Binding {
	target: contactName; property: 'text'
	value: givenName + " " + familyName; when: list.ListView.isCurrentItem
	delayed: true
	}
	\endcode
	*/
	bool QQmlBind::delayed() const
	{
	Q_D(const QQmlBind);
	return d->delayed;
	}

	void QQmlBind::setDelayed(bool delayed)
	{
	Q_D(QQmlBind);
	if (d->delayed == delayed)
	return;

	d->delayed = delayed;

	if (!d->delayed)
	eval();
	}

	/*!
	\qmlproperty enumeration QtQml::Binding::restoreMode
	\since 5.14

	This property can be used to describe if and how the original value should
	be restored when the binding is disabled.

	The possible values are:
	\list
	\li Binding.RestoreNone The original value is not restored at all
	\li Binding.RestoreBinding The original value is restored if it was another
	binding. In that case the old binding is in effect again.
	\li Binding.RestoreValue The original value is restored if it was a plain
	value rather than a binding.
	\li Binding.RestoreBindingOrValue The original value is always restored.
	\endlist

	\warning The default value is Binding.RestoreBinding. This will change in
	Qt 6.0 to Binding.RestoreBindingOrValue.

	If you rely on any specific behavior regarding the restoration of plain
	values when bindings get disabled you should migrate to explicitly set the
	restoreMode.

	Reliance on a restoreMode that doesn't restore the previous binding or value
	for a specific property results in a run-time warning.
	*/
	QQmlBind::RestorationMode QQmlBind::restoreMode() const
	{
	Q_D(const QQmlBind);
	unsigned result = RestoreNone;
	if (d->restoreValue)
	result \|= RestoreValue;
	if (d->restoreBinding)
	result \|= RestoreBinding;
	return RestorationMode(result);
	}

	void QQmlBind::setRestoreMode(RestorationMode newMode)
	{
	Q_D(QQmlBind);
	d->restoreModeExplicit = true;
	if (newMode != restoreMode()) {
	d->restoreValue = (newMode & RestoreValue);
	d->restoreBinding = (newMode & RestoreBinding);
	emit restoreModeChanged();
	}
	}

	void QQmlBind::setTarget(const QQmlProperty &p)
	{
	Q_D(QQmlBind);

	if (Q_UNLIKELY(lcBindingRemoval().isInfoEnabled())) {
	if (QObject *oldObject = d->prop.object()) {
	QMetaProperty prop = oldObject->metaObject()->property(d->prop.index());
	if (prop.hasNotifySignal()) {
	QByteArray signal('2' + prop.notifySignal().methodSignature());
	QObject::disconnect(oldObject, signal.constData(),
	this, SLOT(targetValueChanged()));
	}
	}
	p.connectNotifySignal(this, SLOT(targetValueChanged()));
	}

	d->prop = p;
	}

	void QQmlBind::classBegin()
	{
	Q_D(QQmlBind);
	d->componentComplete = false;
	}

	void QQmlBind::componentComplete()
	{
	Q_D(QQmlBind);
	d->componentComplete = true;
	if (!d->prop.isValid()) {
	setTarget(QQmlProperty(d->obj, d->propName, qmlContext(this)));
	d->validate(this);
	}
	eval();
	}

	void QQmlBind::prepareEval()
	{
	Q_D(QQmlBind);
	if (d->delayed) {
	if (!d->pendingEval)
	QTimer::singleShot(0, this, &QQmlBind::eval);
	d->pendingEval = true;
	} else {
	eval();
	}
	}

	void QQmlBindPrivate::clearPrev()
	{
	prevBind = nullptr;
	v4Value.clear();
	prevValue.clear();
	prevIsVariant = false;
	}

	void QQmlBind::eval()
	{
	Q_D(QQmlBind);
	d->pendingEval = false;
	if (!d->prop.isValid() \|\| d->value.isNull \|\| !d->componentComplete)
	return;

	if (d->when.isValid()) {
	if (!d->when) {
	//restore any previous binding
	if (d->prevBind) {
	if (d->restoreBinding) {
	QQmlAbstractBinding::Ptr p = d->prevBind;
	d->clearPrev(); // Do that before setBinding(), as setBinding() may recurse.
	QQmlPropertyPrivate::setBinding(p.data());
	}
	} else if (!d->v4Value.isEmpty()) {
	if (d->restoreValue) {
	auto propPriv = QQmlPropertyPrivate::get(d->prop);
	QQmlVMEMetaObject *vmemo = QQmlVMEMetaObject::get(propPriv->object);
	Q_ASSERT(vmemo);
	vmemo->setVMEProperty(propPriv->core.coreIndex(), *d->v4Value.valueRef());
	d->clearPrev();
	} else if (!d->restoreModeExplicit) {
	qmlWarning(this)
	<< "Not restoring previous value because restoreMode has not been set."
	<< "This behavior is deprecated."
	<< "In Qt < 6.0 the default is Binding.RestoreBinding."
	<< "In Qt >= 6.0 the default is Binding.RestoreBindingOrValue.";
	}
	} else if (d->prevIsVariant) {
	if (d->restoreValue) {
	d->prop.write(d->prevValue);
	d->clearPrev();
	} else if (!d->restoreModeExplicit) {
	qmlWarning(this)
	<< "Not restoring previous value because restoreMode has not been set."
	<< "This behavior is deprecated."
	<< "In Qt < 6.0 the default is Binding.RestoreBinding."
	<< "In Qt >= 6.0 the default is Binding.RestoreBindingOrValue.";
	}
	}
	return;
	}

	//save any set binding for restoration
	if (!d->prevBind && d->v4Value.isEmpty() && !d->prevIsVariant) {
	// try binding first
	d->prevBind = QQmlPropertyPrivate::binding(d->prop);

	if (!d->prevBind) { // nope, try a V4 value next
	auto propPriv = QQmlPropertyPrivate::get(d->prop);
	auto propData = propPriv->core;
	if (!propPriv->valueTypeData.isValid() && propData.isVarProperty()) {
	QQmlVMEMetaObject *vmemo = QQmlVMEMetaObject::get(propPriv->object);
	Q_ASSERT(vmemo);
	auto retVal = vmemo->vmeProperty(propData.coreIndex());
	d->v4Value = QV4::PersistentValue(vmemo->engine, retVal);
	} else { // nope, use the meta object to get a QVariant
	d->prevValue = d->prop.read();
	d->prevIsVariant = true;
	}
	}
	}

	QQmlPropertyPrivate::removeBinding(d->prop);
	}

	d->writingProperty = true;
	d->prop.write(d->value.value.toVariant());
	d->writingProperty = false;
	}

	void QQmlBind::targetValueChanged()
	{
	Q_D(QQmlBind);
	if (d->writingProperty)
	return;

	if (d->when.isValid() && !d->when)
	return;

	QUrl url;
	quint16 line = 0;

	const QQmlData *ddata = QQmlData::get(this, false);
	if (ddata && ddata->outerContext) {
	url = ddata->outerContext->url();
	line = ddata->lineNumber;
	}

	qCInfo(lcBindingRemoval,
	"The target property of the Binding element created at %s:%d was changed from "
	"elsewhere. This does not overwrite the binding. The target property will still be "
	"updated when the value of the Binding element changes.",
	qPrintable(url.toString()), line);
	}

	QT_END_NAMESPACE

	#include "moc_qqmlbind_p.cpp"