QQmlListReference Class | Qt QML 6.1.0

- Qt 6.1
- Qt QML
- C++ Classes
- QQmlListReference
- Qt 6.1.0 Reference Documentation

# QQmlListReference Class

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

Header: | #include <QQmlListReference>
CMake: | find_package(Qt6 COMPONENTS Qml REQUIRED) target_link_libraries(mytarget PRIVATE Qt6::Qml)
qmake: | QT += qml
Since: | Qt 5.0

- List of all members, including inherited members

## Public Functions

| QQmlListReference(QObject *object, const char *property, QQmlEngine *engine = nullptr)
| QQmlListReference(const QVariant &variant, QQmlEngine *engine = nullptr)
| QQmlListReference()
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
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. A QQmlListReference can be created by passing an object and property name or through a QQmlProperty instance. These two are equivalent:

     QQmlListReference ref1(object, "children");

     QQmlProperty ref2(object, "children");
     QQmlListReference ref2 = qvariant_cast<QQmlListReference>(ref2.read());

Not all QML list properties support all operations. A set of methods, canAppend(), canAt(), canClear() and canCount() allow programs to query whether an operation is supported on a given property.

QML list properties are type-safe. Only QObject's that derive from the correct base class can be assigned to the list. The listElementType() method can be used to query the QMetaObject of the QObject type supported. Attempting to add objects of the incorrect type to a list property will fail.

Like with normal 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 using the count() method before calling at().

## Member Function Documentation

### QQmlListReference::QQmlListReference(QObject *object, const char *property, QQmlEngine *engine = nullptr)

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.

Passing engine is required to access some QML created list properties. If in doubt, and an engine is available, pass it.

### `[since 6.1]` QQmlListReference::QQmlListReference(const QVariant &variant, QQmlEngine *engine = nullptr)

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.

The engine is required to look up the element type, which may be a dynamically created QML type. If it's omitted, only pre-registered types are available.

This function was introduced in Qt 6.1.

### QQmlListReference::QQmlListReference()

Constructs an invalid instance.

### 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 0 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 objects 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.

### 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().

### 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.