qqmllist.cpp

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// 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 "qqmllist.h"
#include "qqmllist_p.h"
#include <QtQml/private/qqmlproperty_p.h>
 
QT_BEGIN_NAMESPACE
 
static bool isObjectCompatible(QObject *object, QQmlListReferencePrivate *d)
{
    if (object) {
        const QQmlMetaObject elementType = d->elementType();
        if (elementType.isNull() || !QQmlMetaObject::canConvert(object, elementType))
            return false;
    }
    return true;
}
 
QQmlListReferencePrivate::QQmlListReferencePrivate()
: refCount(1)
{
}
 
QQmlListReference QQmlListReferencePrivate::init(
        const QQmlListProperty<QObject> &prop, QMetaType propType)
{
    QQmlListReference rv;
 
    if (!prop.object) return rv;
 
    rv.d = new QQmlListReferencePrivate;
    rv.d->object = prop.object;
    rv.d->property = prop;
    rv.d->propertyType = propType;
 
    return rv;
}
 
void QQmlListReferencePrivate::addref()
{
    Q_ASSERT(refCount > 0);
    ++refCount;
}
 
void QQmlListReferencePrivate::release()
{
    Q_ASSERT(refCount > 0);
    --refCount;
    if (!refCount)
        delete this;
}
 
/*!
\class QQmlListReference
\since 5.0
\inmodule QtQml
\brief The QQmlListReference class allows the manipulation of \l QQmlListProperty properties.
 
QQmlListReference allows C++ programs to read from, and assign values to a QML list property in a
simple and type-safe way. The main advantage over using \l QQmlListProperty itself is its type
erasure: QQmlListReference is not a template, but can be used for QQmlListProperties of any type.
Furthermore it watches the owner object for deletion and does not allow the \l QQmlListProperty
to be accessed anymore if its owner has been deleted.
 
You can create a QQmlListReference from either an object and a property name or from a QVariant.
These two are equivalent:
 
\code
QQmlListReference ref1(object, "children");
 
const QVariant var = object->property("children");
QQmlListReference ref2(var);
\endcode
 
Not all QQmlListReferences support all operations. Methods like canAppend(),
canAt(), canClear(), and canCount() allow programs to query whether an
operation is supported on a given property. The availability of the methods
depends on the methods implemented by the underlying \l QQmlListProperty. When
constructing a \l QQmlListProperty by manually passing the accessor
functions you can restrict access to the list by passing nullptr to some of them.
QQmlListReference will recognize those and report them as unavailable.
 
\l{QQmlListReference}s are type-safe.  Only \l{QObject}s that derive of the
correct base class can be added to the list. The listElementType() method can be
used to query the \l QMetaObject of the \l QObject type that can be added.
Attempting to add objects of an incorrect type to a list property will fail.
 
Like with other lists, when accessing a list element by index, it is the
callers responsibility to ensure that it does not request an out of range
element. Use the count() method before calling at() to this effect.
*/
 
/*!
\fn bool QQmlListReference::operator==(const QQmlListReference &other) const
 
Compares this QQmlListReference to \a other, and returns \c true if they are
equal. The two are only considered equal if one was created from the other
via copy assignment or copy construction.
 
\note Independently created references to the same object are not considered
to be equal.
*/
 
/*!
Constructs an invalid instance.
*/
QQmlListReference::QQmlListReference()
: d(nullptr)
{
}
 
#if QT_DEPRECATED_SINCE(6, 4)
/*!
\since 6.1
\obsolete [6.4] Use the constructors without QQmlEngine argument instead.
 
Constructs a QQmlListReference from a QVariant \a variant containing a QQmlListProperty. If
\a variant does not contain a list property, an invalid QQmlListReference is created. If the object
owning the list property is destroyed after the reference is constructed, it will automatically
become invalid.  That is, it is safe to hold QQmlListReference instances even after the object is
deleted.
 
The \a engine is unused.
*/
QQmlListReference::QQmlListReference(const QVariant &variant, [[maybe_unused]] QQmlEngine *engine)
    : QQmlListReference(variant)
{}
 
/*!
\obsolete [6.4] Use the constructors without QQmlEngine argument instead.
 
Constructs a QQmlListReference for \a object's \a property.  If \a property is not a list
property, an invalid QQmlListReference is created.  If \a object is destroyed after
the reference is constructed, it will automatically become invalid.  That is, it is safe to hold
QQmlListReference instances even after \a object is deleted.
 
The \a engine is unused.
*/
QQmlListReference::QQmlListReference(QObject *object, const char *property,
                                     [[maybe_unused]] QQmlEngine *engine)
    : QQmlListReference(object, property)
{}
#endif
 
/*!
\since 6.1
 
Constructs a QQmlListReference from a QVariant \a variant containing a QQmlListProperty. If
\a variant does not contain a list property, an invalid QQmlListReference is created. If the object
owning the list property is destroyed after the reference is constructed, it will automatically
become invalid.  That is, it is safe to hold QQmlListReference instances even after the object is
deleted.
*/
QQmlListReference::QQmlListReference(const QVariant &variant)
    : d(nullptr)
{
    const QMetaType t = variant.metaType();
    if (!(t.flags() & QMetaType::IsQmlList))
        return;
 
    d = new QQmlListReferencePrivate;
    d->propertyType = t;
 
    d->property.~QQmlListProperty();
    t.construct(&d->property, variant.constData());
 
    d->object = d->property.object;
}
 
/*!
Constructs a QQmlListReference for \a object's \a property.  If \a property is not a list
property, an invalid QQmlListReference is created.  If \a object is destroyed after
the reference is constructed, it will automatically become invalid.  That is, it is safe to hold
QQmlListReference instances even after \a object is deleted.
*/
QQmlListReference::QQmlListReference(QObject *object, const char *property)
    : d(nullptr)
{
    if (!object || !property) return;
 
    QQmlPropertyData local;
    const QQmlPropertyData *data =
        QQmlPropertyCache::property(object, QLatin1String(property), nullptr, &local);
 
    if (!data || !data->isQList()) return;
 
    d = new QQmlListReferencePrivate;
    d->object = object;
    d->propertyType = data->propType();
 
    void *args[] = { &d->property, nullptr };
    QMetaObject::metacall(object, QMetaObject::ReadProperty, data->coreIndex(), args);
}
 
/*! \internal */
QQmlListReference::QQmlListReference(const QQmlListReference &o)
: d(o.d)
{
    if (d) d->addref();
}
 
/*! \internal */
QQmlListReference &QQmlListReference::operator=(const QQmlListReference &o)
{
    if (o.d) o.d->addref();
    if (d) d->release();
    d = o.d;
    return *this;
}
 
/*! \internal */
QQmlListReference::~QQmlListReference()
{
    if (d) d->release();
}
 
/*!
Returns true if the instance refers to a valid list property, otherwise false.
*/
bool QQmlListReference::isValid() const
{
    return d && d->object;
}
 
/*!
Returns the list property's object. Returns \nullptr if the reference is invalid.
*/
QObject *QQmlListReference::object() const
{
    if (isValid()) return d->object;
    else return nullptr;
}
 
/*!
Returns the QMetaObject for the elements stored in the list property,
or \nullptr if the reference is invalid.
 
The QMetaObject can be used ahead of time to determine whether a given instance can be added
to a list. If you didn't pass an engine on construction this may return nullptr.
*/
const QMetaObject *QQmlListReference::listElementType() const
{
    return isValid() ? d->elementType() : nullptr;
}
 
/*!
Returns true if the list property can be appended to, otherwise false.  Returns false if the
reference is invalid.
 
\sa append()
*/
bool QQmlListReference::canAppend() const
{
    return (isValid() && d->property.append);
}
 
/*!
Returns true if the list property can queried by index, otherwise false.  Returns false if the
reference is invalid.
 
\sa at()
*/
bool QQmlListReference::canAt() const
{
    return (isValid() && d->property.at);
}
 
/*!
Returns true if the list property can be cleared, otherwise false.  Returns false if the
reference is invalid.
 
\sa clear()
*/
bool QQmlListReference::canClear() const
{
    return (isValid() && d->property.clear);
}
 
/*!
Returns true if the list property can be queried for its element count, otherwise false.
Returns false if the reference is invalid.
 
\sa count()
*/
bool QQmlListReference::canCount() const
{
    return (isValid() && d->property.count);
}
 
/*!
Returns true if items in the list property can be replaced, otherwise false.
Returns false if the reference is invalid.
 
\sa replace()
*/
bool QQmlListReference::canReplace() const
{
    return (isValid() && d->property.replace);
}
 
/*!
Returns true if the last item can be removed from the list property, otherwise false.
Returns false if the reference is invalid.
 
\sa removeLast()
*/
bool QQmlListReference::canRemoveLast() const
{
    return (isValid() && d->property.removeLast);
}
 
/*!
    Return true if at(), count(), append(), and either clear() or removeLast()
    are implemented, so you can manipulate the list.
 
    Mind that replace() and removeLast() can be emulated by stashing all
    items and rebuilding the list using clear() and append(). Therefore,
    they are not required for the list to be manipulable. Furthermore,
    clear() can be emulated using removeLast().
 
\sa isReadable(), at(), count(), append(), clear(), replace(), removeLast()
*/
bool QQmlListReference::isManipulable() const
{
    return (isValid()
            && d->property.append
            && d->property.count
            && d->property.at
            && d->property.clear);
}
 
 
/*!
    Return true if at() and count() are implemented, so you can access the elements.
 
\sa isManipulable(), at(), count()
*/
bool QQmlListReference::isReadable() const
{
    return (isValid() && d->property.count && d->property.at);
}
 
/*!
Appends \a object to the list.  Returns true if the operation succeeded, otherwise false.
 
\sa canAppend()
*/
bool QQmlListReference::append(QObject *object) const
{
    if (!canAppend()) return false;
 
    if (!isObjectCompatible(object, d))
        return false;
 
    d->property.append(&d->property, object);
 
    return true;
}
 
/*!
Returns the list element at \a index, or \nullptr if the operation failed.
 
\sa canAt()
*/
QObject *QQmlListReference::at(qsizetype index) const
{
    if (!canAt()) return nullptr;
 
    return d->property.at(&d->property, index);
}
 
/*!
Clears the list.  Returns true if the operation succeeded, otherwise false.
 
\sa canClear()
*/
bool QQmlListReference::clear() const
{
    if (!canClear()) return false;
 
    d->property.clear(&d->property);
 
    return true;
}
 
/*!
Returns the number of items in the list, or 0 if the operation failed.
*/
qsizetype QQmlListReference::count() const
{
    if (!canCount()) return 0;
 
    return d->property.count(&d->property);
}
 
/*!
\fn qsizetype QQmlListReference::size() const
\since 6.2
Returns the number of items in the list, or 0 if the operation failed.
*/
 
/*!
Replaces the item at \a index in the list with \a object.
Returns true if the operation succeeded, otherwise false.
 
\sa canReplace()
*/
bool QQmlListReference::replace(qsizetype index, QObject *object) const
{
    if (!canReplace())
        return false;
 
    if (!isObjectCompatible(object, d))
        return false;
 
    d->property.replace(&d->property, index, object);
    return true;
}
 
/*!
Removes the last item in the list.
Returns true if the operation succeeded, otherwise false.
 
\sa canRemoveLast()
*/
bool QQmlListReference::removeLast() const
{
    if (!canRemoveLast())
        return false;
 
    d->property.removeLast(&d->property);
    return true;
}
 
/*!
\class QQmlListProperty
\since 5.0
\inmodule QtQml
\brief The QQmlListProperty class allows applications to expose list-like
properties of QObject-derived classes to QML.
 
QML has many list properties, where more than one object value can be assigned.
The use of a list property from QML looks like this:
 
\code
FruitBasket {
    fruit: [
        Apple {},
        Orange{},
        Banana{}
    ]
}
\endcode
 
The QQmlListProperty encapsulates a group of function pointers that represent the
set of actions QML can perform on the list - adding items, retrieving items and
clearing the list.  In the future, additional operations may be supported.  All
list properties must implement the append operation, but the rest are optional.
 
To provide a list property, a C++ class must implement the operation callbacks,
and then return an appropriate QQmlListProperty value from the property getter.
List properties should have no setter.  In the example above, the Q_PROPERTY()
declarative will look like this:
 
\code
Q_PROPERTY(QQmlListProperty<Fruit> fruit READ fruit)
\endcode
 
QML list properties are type-safe - in this case \c {Fruit} is a QObject type that
\c {Apple}, \c {Orange} and \c {Banana} all derive from.
 
You can use \l{QQmlListReference} to manipulate a QQmlListProperty from C++ using
a slightly more ergonomic API, at the cost of some overhead.
 
\sa {Chapter 5: Using List Property Types}, QQmlListReference
*/
 
/*!
    \macro QML_LIST_PROPERTY_ASSIGN_BEHAVIOR_APPEND
    \relates QQmlListProperty
 
    This macro defines the behavior of the list properties of this class to Append.
    When assigning the property in a derived type, the values are appended
    to those of the base class. This is the default behavior.
 
    \snippet code/src_qml_qqmllist.cpp 0
 
    \sa QML_LIST_PROPERTY_ASSIGN_BEHAVIOR_REPLACE_IF_NOT_DEFAULT
    \sa QML_LIST_PROPERTY_ASSIGN_BEHAVIOR_REPLACE
    \sa {Defining Object Types through QML Documents}
*/
 
/*!
    \macro QML_LIST_PROPERTY_ASSIGN_BEHAVIOR_REPLACE_IF_NOT_DEFAULT
    \relates QQmlListProperty
 
    This macro defines the behavior of the list properties of this class to
    ReplaceIfNotDefault.
    When assigning the property in a derived type, the values replace those of
    the base class unless it's the default property.
    In the case of the default property, values are appended to those of the base class.
 
    \snippet code/src_qml_qqmllist.cpp 1
 
    \sa QML_LIST_PROPERTY_ASSIGN_BEHAVIOR_APPEND
    \sa QML_LIST_PROPERTY_ASSIGN_BEHAVIOR_REPLACE
    \sa {Defining Object Types through QML Documents}
*/
 
/*!
    \macro QML_LIST_PROPERTY_ASSIGN_BEHAVIOR_REPLACE
    \relates QQmlListProperty
 
    This macro defines the behavior of the list properties of this class to Replace.
    When assigning the property in a derived type, the values replace those
    of the base class.
 
    \snippet code/src_qml_qqmllist.cpp 2
 
    \sa QML_LIST_PROPERTY_ASSIGN_BEHAVIOR_APPEND
    \sa QML_LIST_PROPERTY_ASSIGN_BEHAVIOR_REPLACE_IF_NOT_DEFAULT
    \sa {Defining Object Types through QML Documents}
*/
 
/*!
\fn template<typename T> QQmlListProperty<T>::QQmlListProperty()
\internal
*/
 
/*!
\fn template<typename T> QQmlListProperty<T>::QQmlListProperty(QObject *object, QList<T *> &list)
\deprecated
 
Convenience constructor for making a QQmlListProperty value from an existing
QList \a list. The \a object owning the list and the \a list itself must be
provided and kept alive as long as you are holding a QQmlListProperty referring
to them.
 
This constructor synthesizes the removeLast() and replace() methods
introduced in Qt 5.15, using count(), at(), clear(), and append(). This is slow.
If you intend to manipulate the list beyond clearing it, you should explicitly
provide these methods.
*/
 
/*!
\fn template<typename T> QQmlListProperty<T>::QQmlListProperty(QObject *object, QList<T *> *list)
\since 5.15
 
Convenience constructor for making a QQmlListProperty value from an existing
QList \a list. The \a object owning the list and the \a list itself must be
provided and kept alive as long as you are holding a QQmlListProperty referring
to them.
 
This is the easiest and safest way to provide a QQmlListProperty backed by a QList
and should be used in most cases. A typical invocation looks like this:
 
\snippet tutorials/extending-qml/chapter5-listproperties/piechart.cpp 0
*/
 
/*!
\fn template<typename T> QQmlListProperty<T>::QQmlListProperty(QObject *object, void *data,
                                    CountFunction count, AtFunction at)
 
Construct a readonly QQmlListProperty from a set of operation functions
\a count and \a at. An opaque \a data handle may be passed which can be
accessed from within the operation functions.  The list property
remains valid while the \a object owning the list property exists.
*/
 
/*!
\fn template<typename T> QQmlListProperty<T>::QQmlListProperty(QObject *object, void *data, AppendFunction append,
                                     CountFunction count, AtFunction at,
                                     ClearFunction clear)
 
Construct a QQmlListProperty from a set of operation functions \a append,
\a count, \a at, and \a clear.  An opaque \a data handle may be passed which
can be accessed from within the operation functions.  The list property
remains valid while the \a object owning the list property exists.
 
Null pointers can be passed for any function. If any null pointers are passed in, the list
will be neither designable nor alterable by the debugger. It is recommended to provide valid
pointers for all functions.
 
\note The resulting QQmlListProperty will synthesize the removeLast() and
replace() methods using \a count, \a at, \a clear, and \a append if all of those
are given. This is slow. If you intend to manipulate the list beyond clearing it,
you should explicitly provide these methods.
*/
 
/*!
\fn template<typename T> QQmlListProperty<T>::QQmlListProperty(
        QObject *object, void *data, AppendFunction append, CountFunction count,
        AtFunction at, ClearFunction clear, ReplaceFunction replace,
        RemoveLastFunction removeLast)
 
Construct a QQmlListProperty from a set of operation functions \a append,
\a count, \a at, \a clear, \a replace, and \removeLast. An opaque \a data handle
may be passed which can be accessed from within the operation functions. The
list property remains valid while the \a object owning the list property
exists.
 
Null pointers can be passed for any function, causing the respective function to
be synthesized using the others, if possible. QQmlListProperty can synthesize
\list
    \li \a clear using \a count and \a removeLast
    \li \a replace using \a count, \a at, \a clear, and \a append
    \li \a replace using \a count, \a at, \a removeLast, and \a append
    \li \a removeLast using \a count, \a at, \a clear, and \a append
\endlist
if those are given. This is slow, but if your list does not natively provide
faster options for these primitives, you may want to use the synthesized ones.
 
Furthermore, if either of \a count, \a at, \a append, and \a clear are neither
given explicitly nor synthesized, the list will be neither designable nor
alterable by the debugger. It is recommended to provide enough valid pointers
to avoid this situation.
*/
 
/*!
\typedef QQmlListProperty::AppendFunction
 
Synonym for \c {void (*)(QQmlListProperty<T> *property, T *value)}.
 
Append the \a value to the list \a property.
*/
 
/*!
\typedef QQmlListProperty::CountFunction
 
Synonym for \c {qsizetype (*)(QQmlListProperty<T> *property)}.
 
Return the number of elements in the list \a property.
*/
 
/*!
\fn template<typename T> bool QQmlListProperty<T>::operator==(const QQmlListProperty &other) const
 
Returns true if this QQmlListProperty is equal to \a other, otherwise false.
*/
 
/*!
\typedef QQmlListProperty::AtFunction
 
Synonym for \c {T *(*)(QQmlListProperty<T> *property, qsizetype index)}.
 
Return the element at position \a index in the list \a property.
*/
 
/*!
\typedef QQmlListProperty::ClearFunction
 
Synonym for \c {void (*)(QQmlListProperty<T> *property)}.
 
Clear the list \a property.
*/
 
/*!
\typedef QQmlListProperty::ReplaceFunction
 
Synonym for \c {void (*)(QQmlListProperty<T> *property, qsizetype index, T *value)}.
 
Replace the element at position \a index in the list \a property with \a value.
*/
 
/*!
\typedef QQmlListProperty::RemoveLastFunction
 
Synonym for \c {void (*)(QQmlListProperty<T> *property)}.
 
Remove the last element from the list \a property.
*/
 
/*!
\variable QQmlListProperty::object
\brief This field holds the \e owner of the QQmlListProperty
 
When manually implementing the accessor methods, you may need to use this field
for retrieving the content of the manipulated list.
*/
 
/*!
\variable QQmlListProperty::data
\brief This field can hold an arbitrary data pointer
 
If you manually implement the accessor methods and need to store custom data,
you can pass an arbitrary pointer to the QQmlListProperty constructor and
retrieve it from the \e data field when accessing the same QQmlListProperty
later.
 
A \l{QQmlListProperty(QObject *object, QList<T *> *list)}{QQmlListProperty constructed from a QList pointer}
uses this field to store the pointer to the list itself, as it cannot directly
access the list contents from the owner.
 
*/
 
QT_END_NAMESPACE