qqmlcontext.cpp

Go to the documentation of this file.

// Copyright (C) 2016 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
 
#include "qqmlcontext_p.h"
#include "qqmlcomponentattached_p.h"
 
#include "qqmlcomponent_p.h"
#include "qqmlexpression_p.h"
#include "qqmlengine_p.h"
#include "qqmlengine.h"
#include "qqmlinfo.h"
#include "qqmlabstracturlinterceptor.h"
 
#include <qjsengine.h>
#include <QtCore/qvarlengtharray.h>
#include <private/qmetaobject_p.h>
#include <QtCore/qdebug.h>
 
QT_BEGIN_NAMESPACE
 
/*!
    \class QQmlContext
    \brief The QQmlContext class defines a context within a QML engine.
    \inmodule QtQml
 
    Contexts hold the objects identified by \e id in a QML document. You
    can use \l{nameForObject()} and \l{objectForName()} to retrieve them.
 
    \note It is the responsibility of the creator to delete any QQmlContext it
    constructs. If a QQmlContext is no longer needed, it must be destroyed
    explicitly. The simplest way to ensure this is to give the QQmlContext a
    \l{QObject::setParent()}{parent}.
 
    \section2 The Context Hierarchy
 
    Contexts form a hierarchy. The root of this hierarchy is the QML engine's
    \l {QQmlEngine::rootContext()}{root context}. Each QML component creates its
    own context when instantiated and some QML elements create extra contexts
    for themselves.
 
    While QML objects instantiated in a context are not strictly owned by that
    context, their bindings are.  If a context is destroyed, the property bindings of
    outstanding QML objects will stop evaluating.
 
    \section2 Context Properties
 
    Contexts also allow data to be exposed to the QML components instantiated
    by the QML engine. Such data is invisible to any tooling, including the
    \l{Qt Quick Compiler} and to future readers of the QML documents in
    question. It will only be exposed if the QML component is instantiated in
    the specific C++ context you are envisioning. In other places, different
    context data may be exposed instead.
 
    Instead of using the QML context to expose data to your QML components, you
    should either create additional object properties to hold the data or use
    \l{QML_SINGLETON}{singletons}. See
    \l{qtqml-cppintegration-exposecppstate.html}{Exposing C++ State to QML} for
    a detailed explanation.
 
    Each QQmlContext contains a set of properties, distinct from its QObject
    properties, that allow data to be explicitly bound to a context by name.  The
    context properties can be defined and updated by calling
    QQmlContext::setContextProperty().
 
    To simplify binding and maintaining larger data sets, a context object can be set
    on a QQmlContext.  All the properties of the context object are available
    by name in the context, as though they were all individually added through calls
    to QQmlContext::setContextProperty().  Changes to the property's values are
    detected through the property's notify signal.  Setting a context object is both
    faster and easier than manually adding and maintaining context property values.
 
    All properties added explicitly by QQmlContext::setContextProperty() take
    precedence over the context object's properties.
 
    Child contexts inherit the context properties of their parents; if a child
    context sets a context property that already exists in its parent, the new
    context property overrides that of the parent.
 
    \warning Setting the context object or adding new context properties after
    an object has been created in that context is an expensive operation
    (essentially forcing all bindings to re-evaluate). Thus, if you need to use
    context properties, you should at least complete the "setup" of the context
    before using it to create any objects.
 
    \sa {qtqml-cppintegration-exposecppattributes.html}{Exposing Attributes of C++ Types to QML}
*/
 
/*! \internal */
QQmlContext::QQmlContext(QQmlEngine *e, bool)
    : QObject(*(new QQmlContextPrivate(this, QQmlRefPointer<QQmlContextData>(), e)))
{
}
 
/*!
    Create a new QQmlContext as a child of \a engine's root context, and the
    QObject \a parent.
*/
QQmlContext::QQmlContext(QQmlEngine *engine, QObject *parent)
    : QObject(*(new QQmlContextPrivate(this, engine
                                       ? QQmlContextData::get(engine->rootContext())
                                       : QQmlRefPointer<QQmlContextData>())), parent)
{
}
 
/*!
    Create a new QQmlContext with the given \a parentContext, and the
    QObject \a parent.
*/
QQmlContext::QQmlContext(QQmlContext *parentContext, QObject *parent)
    : QObject(*(new QQmlContextPrivate(this, parentContext
                                       ? QQmlContextData::get(parentContext)
                                       : QQmlRefPointer<QQmlContextData>())), parent)
{
}
 
/*!
    \internal
*/
QQmlContext::QQmlContext(QQmlContextPrivate &dd, QObject *parent)
    : QObject(dd, parent)
{
}
 
/*!
    Destroys the QQmlContext.
 
    Any expressions, or sub-contexts dependent on this context will be
    invalidated, but not destroyed (unless they are parented to the QQmlContext
    object).
 */
QQmlContext::~QQmlContext()
{
    Q_D(QQmlContext);
    d->m_data->clearPublicContext();
}
 
/*!
    Returns whether the context is valid.
 
    To be valid, a context must have a engine, and it's contextObject(), if any,
    must not have been deleted.
*/
bool QQmlContext::isValid() const
{
    Q_D(const QQmlContext);
    return d->m_data->isValid();
}
 
/*!
    Return the context's QQmlEngine, or \nullptr if the context has no QQmlEngine or the
    QQmlEngine was destroyed.
*/
QQmlEngine *QQmlContext::engine() const
{
    Q_D(const QQmlContext);
    return d->m_data->engine();
}
 
/*!
    Return the context's parent QQmlContext, or \nullptr if this context has no
    parent or if the parent has been destroyed.
*/
QQmlContext *QQmlContext::parentContext() const
{
    Q_D(const QQmlContext);
 
    if (QQmlRefPointer<QQmlContextData> parent = d->m_data->parent())
        return parent->asQQmlContext();
    return nullptr;
}
 
/*!
    Return the context object, or \nullptr if there is no context object.
*/
QObject *QQmlContext::contextObject() const
{
    Q_D(const QQmlContext);
    return d->m_data->contextObject();
}
 
/*!
    Set the context \a object.
 
    \note You should not use context objects to inject values into your QML
          components. Use singletons or regular object properties instead.
*/
void QQmlContext::setContextObject(QObject *object)
{
    Q_D(QQmlContext);
 
    QQmlRefPointer<QQmlContextData> data = d->m_data;
 
    if (data->isInternal()) {
        qWarning("QQmlContext: Cannot set context object for internal context.");
        return;
    }
 
    if (!data->isValid()) {
        qWarning("QQmlContext: Cannot set context object on invalid context.");
        return;
    }
 
    data->setContextObject(object);
    data->refreshExpressions();
}
 
/*!
    Set a the \a value of the \a name property on this context.
 
    \note You should not use context properties to inject values into your QML
          components. Use singletons or regular object properties instead.
*/
void QQmlContext::setContextProperty(const QString &name, const QVariant &value)
{
    Q_D(QQmlContext);
    if (d->notifyIndex() == -1)
        d->setNotifyIndex(QMetaObjectPrivate::absoluteSignalCount(&QQmlContext::staticMetaObject));
 
    QQmlRefPointer<QQmlContextData> data = d->m_data;
 
    if (data->isInternal()) {
        qWarning("QQmlContext: Cannot set property on internal context.");
        return;
    }
 
    if (!data->isValid()) {
        qWarning("QQmlContext: Cannot set property on invalid context.");
        return;
    }
 
    if (bool isNumber = false; name.toUInt(&isNumber), isNumber) {
        qWarning("QQmlContext: Using numbers as context properties will be disallowed in a future Qt version.");
        QT7_ONLY(return;)
    }
 
    int idx = data->propertyIndex(name);
    if (idx == -1) {
        data->addPropertyNameAndIndex(name, data->numIdValues() + d->numPropertyValues());
        d->appendPropertyValue(value);
        data->refreshExpressions();
    } else {
        d->setPropertyValue(idx, value);
        QMetaObject::activate(this, d->notifyIndex(), idx, nullptr);
    }
 
    if (auto *obj = qvariant_cast<QObject *>(value)) {
        connect(obj, &QObject::destroyed, this, [d, name](QObject *destroyed) {
            d->dropDestroyedQObject(name, destroyed);
        });
    }
}
 
/*!
    Set the \a value of the \a name property on this context.
 
    QQmlContext does \b not take ownership of \a value.
 
    \note You should not use context properties to inject values into your QML
          components. Use singletons or regular object properties instead.
*/
void QQmlContext::setContextProperty(const QString &name, QObject *value)
{
    setContextProperty(name, QVariant::fromValue(value));
}
 
/*!
    \since 5.11
 
    Set a batch of \a properties on this context.
 
    Setting all properties in one batch avoids unnecessary
    refreshing  expressions, and is therefore recommended
    instead of calling \l setContextProperty() for each individual property.
 
    \note You should not use context properties to inject values into your QML
          components. Use singletons or regular object properties instead.
 
    \sa QQmlContext::setContextProperty()
*/
void QQmlContext::setContextProperties(const QList<PropertyPair> &properties)
{
    Q_D(const QQmlContext);
 
    QQmlRefPointer<QQmlContextData> data = d->m_data;
    QQmlJavaScriptExpression *expressions = data->takeExpressions();
    QQmlRefPointer<QQmlContextData> childContexts = data->takeChildContexts();
 
    for (const auto &property : properties)
        setContextProperty(property.name, property.value);
 
    data->setExpressions(expressions);
    data->setChildContexts(childContexts);
    data->refreshExpressions();
}
 
/*!
    \since 5.11
 
    \class QQmlContext::PropertyPair
    \inmodule QtQml
 
    This struct contains a property name and a property value.
    It is used as a parameter for the \c setContextProperties function.
 
    \sa QQmlContext::setContextProperties()
*/
 
static bool readObjectProperty(
        const QQmlRefPointer<QQmlContextData> &data, QObject *object, const QString &name,
        QVariant *target)
{
    QQmlPropertyData local;
    if (const QQmlPropertyData *property = QQmlPropertyCache::property(object, name, data, &local)) {
        *target = object->metaObject()->property(property->coreIndex()).read(object);
        return true;
    }
    return false;
}
 
/*!
  Returns the value of the \a name property for this context as a QVariant.
  If you know that the property you're looking for is a QObject assigned using
  a QML id in the current context, \l objectForName() is more convenient and
  faster. In contrast to \l objectForName() and \l nameForObject(), this method
  does traverse the context hierarchy and searches in parent contexts if the
  \a name is not found in the current one. It also considers any
  \l contextObject() you may have set.
 
  \sa objectForName(), nameForObject(), contextObject()
 */
QVariant QQmlContext::contextProperty(const QString &name) const
{
    Q_D(const QQmlContext);
 
    const QQmlRefPointer<QQmlContextData> data = d->m_data;
 
    const int idx = data->propertyIndex(name);
    if (idx == -1) {
        if (QObject *obj = data->contextObject()) {
            QVariant value;
            if (readObjectProperty(data, obj, name, &value))
                return value;
        }
 
        if (parentContext())
            return parentContext()->contextProperty(name);
    } else {
        if (idx >= d->numPropertyValues())
            return QVariant::fromValue(data->idValue(idx - d->numPropertyValues()));
        else
            return d->propertyValue(idx);
    }
 
    return QVariant();
}
 
/*!
  Returns the name of \a object in this context, or an empty string if \a object
  is not named in the context. Objects are named by \l setContextProperty(), or
  as properties of a context object, or by ids in the case of QML created
  contexts.
 
  If the object has multiple names, the first is returned.
 
  In contrast to \l contextProperty(), this method does not traverse the
  context hierarchy. If the name is not found in the current context, an empty
  String is returned.
 
  \sa contextProperty(), objectForName()
*/
QString QQmlContext::nameForObject(const QObject *object) const
{
    Q_D(const QQmlContext);
 
    return d->m_data->findObjectId(object);
}
 
/*!
  \since 6.2
 
  Returns the object for a given \a name in this context. Returns nullptr if
  \a name is not available in the context or if the value associated with
  \a name is not a QObject. Objects are named by \l setContextProperty(),
  or as properties of a context object, or by ids in the case of QML created
  contexts. In contrast to \l contextProperty(), this method does not traverse
  the context hierarchy. If the name is not found in the current context,
  nullptr is returned.
 
  \sa contextProperty(), nameForObject()
*/
QObject *QQmlContext::objectForName(const QString &name) const
{
    Q_D(const QQmlContext);
 
    QQmlRefPointer<QQmlContextData> data = d->m_data;
    if (const int propertyIndex = data->propertyIndex(name); propertyIndex >= 0) {
        const int numPropertyValues = d->numPropertyValues();
        if (propertyIndex < numPropertyValues)
            return qvariant_cast<QObject *>(d->propertyValue(propertyIndex));
        return data->idValue(propertyIndex - numPropertyValues);
    }
 
    if (QObject *obj = data->contextObject()) {
        QVariant result;
        if (readObjectProperty(data, obj, name, &result))
            return qvariant_cast<QObject *>(result);
    }
 
    return nullptr;
}
 
/*!
    Resolves the URL \a src relative to the URL of the
    containing component.
 
    \sa QQmlEngine::baseUrl(), setBaseUrl()
*/
QUrl QQmlContext::resolvedUrl(const QUrl &src) const
{
    Q_D(const QQmlContext);
    return d->m_data->resolvedUrl(src);
}
 
/*!
    Explicitly sets the url resolvedUrl() will use for relative references to \a baseUrl.
 
    Calling this function will override the url of the containing
    component used by default.
 
    \sa resolvedUrl()
*/
void QQmlContext::setBaseUrl(const QUrl &baseUrl)
{
    Q_D(QQmlContext);
    d->m_data->setBaseUrl(baseUrl);
    d->m_data->setBaseUrlString(baseUrl.toString());
}
 
/*!
    Returns the base url of the component, or the containing component
    if none is set.
*/
QUrl QQmlContext::baseUrl() const
{
    Q_D(const QQmlContext);
    return d->m_data->baseUrl();
}
 
/*!
 * \internal
 */
QJSValue QQmlContext::importedScript(const QString &name) const
{
    Q_D(const QQmlContext);
 
    QV4::ExecutionEngine *v4 = engine()->handle();
    QQmlTypeNameCache::Result r = d->m_data->imports()->query(name, v4->typeLoader());
    QV4::Scope scope(v4);
    QV4::ScopedObject scripts(scope, d->m_data->importedScripts());
    return scripts ? QJSValuePrivate::fromReturnedValue(scripts->get(r.scriptIndex))
                   : QJSValue(QJSValue::UndefinedValue);
}
 
qsizetype QQmlContextPrivate::context_count(QQmlListProperty<QObject> *prop)
{
    QQmlContext *context = static_cast<QQmlContext*>(prop->object);
    QQmlContextPrivate *d = QQmlContextPrivate::get(context);
    int contextProperty = (int)(quintptr)prop->data;
 
    if (d->propertyValue(contextProperty).userType() != qMetaTypeId<QList<QObject*> >())
        return 0;
    else
        return ((const QList<QObject> *)d->propertyValue(contextProperty).constData())->size();
}
 
QObject *QQmlContextPrivate::context_at(QQmlListProperty<QObject> *prop, qsizetype index)
{
    QQmlContext *context = static_cast<QQmlContext*>(prop->object);
    QQmlContextPrivate *d = QQmlContextPrivate::get(context);
    int contextProperty = (int)(quintptr)prop->data;
 
    if (d->propertyValue(contextProperty).userType() != qMetaTypeId<QList<QObject*> >())
        return nullptr;
    else
        return ((const QList<QObject*> *)d->propertyValue(contextProperty).constData())->at(index);
}
 
void QQmlContextPrivate::dropDestroyedQObject(const QString &name, QObject *destroyed)
{
    if (!m_data->isValid())
        return;
 
    const int idx = m_data->propertyIndex(name);
    Q_ASSERT(idx >= 0);
    if (qvariant_cast<QObject *>(propertyValue(idx)) != destroyed)
        return;
 
    setPropertyValue(idx, QVariant::fromValue<QObject *>(nullptr));
    QMetaObject::activate(q_func(), notifyIndex(), idx, nullptr);
}
 
void QQmlContextPrivate::emitDestruction()
{
    m_data->emitDestruction();
}
 
// m_data is owned by the public context. When the public context is reset to nullptr, it will be
// deref'd. It's OK to pass a half-created publicContext here. We will not dereference it during
// construction.
QQmlContextPrivate::QQmlContextPrivate(
        QQmlContext *publicContext, const QQmlRefPointer<QQmlContextData> &parent,
        QQmlEngine *engine) :
    m_data(new QQmlContextData(QQmlContextData::OwnedByPublicContext, publicContext,
                               parent, engine))
{
    Q_ASSERT(publicContext != nullptr);
}
 
QT_END_NAMESPACE
 
#include "moc_qqmlcontext.cpp"