QQmlListReference Class | Qt Qml | Qt 6.12.0
Description: The QQmlListReference class allows the manipulation of QQmlListProperty properties.
Keywords: class

- Qt 6.12
- Qt Qml
- C++ Classes
- QQmlListReference
- Qt 6.12.0 Reference Documentation

# QQmlListReference Class

The QQmlListReference class allows the manipulation of QQmlListProperty properties. More...

Header: | `#include <QQmlListReference>`
CMake: | `find_package(Qt6 REQUIRED COMPONENTS Qml)` `target_link_libraries(mytarget PRIVATE Qt6::Qml)`
qmake: | `QT += qml`

- List of all members, including inherited members
- Deprecated members

## Public Functions

| QQmlListReference()
`(since 6.1)` | QQmlListReference(const QVariant &variant)
| QQmlListReference(QObject *object, const char *property)
bool | append(QObject *object) const
QObject * | at(qsizetype index) const
bool | canAppend() const
bool | canAt() const
bool | canClear() const
bool | canCount() const
bool | canRemoveLast() const
bool | canReplace() const
bool | clear() const
qsizetype | count() const
bool | isManipulable() const
bool | isReadable() const
bool | isValid() const
const QMetaObject * | listElementType() const
QObject * | object() const
bool | removeLast() const
bool | replace(qsizetype index, QObject *object) const
`(since 6.2)` qsizetype | size() const
bool | operator==(const QQmlListReference &other) const

## Detailed Description

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 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 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:

     QQmlListReference ref1(object, "children");

     const QVariant var = object->property("children");
     QQmlListReference ref2(var);

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 QQmlListProperty. When constructing a 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.

QQmlListReferences are type-safe. Only QObjects that derive of the correct base class can be added to the list. The listElementType() method can be used to query the QMetaObject of the 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.

## Member Function Documentation

### QQmlListReference::QQmlListReference()

Constructs an invalid instance.

### `[explicit, since 6.1]` QQmlListReference::QQmlListReference(const QVariant &variant)

Constructs a QQmlListReference from a QVariant variant containing a QQmlListProperty. If 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.

This function was introduced in Qt 6.1.

### QQmlListReference::QQmlListReference(QObject *object, const char *property)

Constructs a QQmlListReference for object's property. If property is not a list property, an invalid QQmlListReference is created. If object is destroyed after the reference is constructed, it will automatically become invalid. That is, it is safe to hold QQmlListReference instances even after object is deleted.

### bool QQmlListReference::append(QObject *object) const

Appends object to the list. Returns true if the operation succeeded, otherwise false.

See also canAppend().

### QObject *QQmlListReference::at(qsizetype index) const

Returns the list element at index, or `nullptr` if the operation failed.

See also canAt().

### bool QQmlListReference::canAppend() const

Returns true if the list property can be appended to, otherwise false. Returns false if the reference is invalid.

See also append().

### bool QQmlListReference::canAt() const

Returns true if the list property can queried by index, otherwise false. Returns false if the reference is invalid.

See also at().

### bool QQmlListReference::canClear() const

Returns true if the list property can be cleared, otherwise false. Returns false if the reference is invalid.

See also clear().

### bool QQmlListReference::canCount() const

Returns true if the list property can be queried for its element count, otherwise false. Returns false if the reference is invalid.

See also count().

### bool QQmlListReference::canRemoveLast() const

Returns true if the last item can be removed from the list property, otherwise false. Returns false if the reference is invalid.

See also removeLast().

### bool QQmlListReference::canReplace() const

Returns true if items in the list property can be replaced, otherwise false. Returns false if the reference is invalid.

See also replace().

### bool QQmlListReference::clear() const

Clears the list. Returns true if the operation succeeded, otherwise false.

See also canClear().

### qsizetype QQmlListReference::count() const

Returns the number of items in the list, or 0 if the operation failed.

### bool QQmlListReference::isManipulable() const

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().

See also isReadable(), at(), count(), append(), clear(), replace(), and removeLast().

### bool QQmlListReference::isReadable() const

Return true if at() and count() are implemented, so you can access the elements.

See also isManipulable(), at(), and count().

### bool QQmlListReference::isValid() const

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

### const QMetaObject *QQmlListReference::listElementType() const

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.

### QObject *QQmlListReference::object() const

Returns the list property's object. Returns `nullptr` if the reference is invalid.

### bool QQmlListReference::removeLast() const

Removes the last item in the list. Returns true if the operation succeeded, otherwise false.

See also canRemoveLast().

### bool QQmlListReference::replace(qsizetype index, QObject *object) const

Replaces the item at index in the list with object. Returns true if the operation succeeded, otherwise false.

See also canReplace().

### `[since 6.2]` qsizetype QQmlListReference::size() const

Returns the number of items in the list, or 0 if the operation failed.

This function was introduced in Qt 6.2.

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

Compares this QQmlListReference to other, and returns `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.