Qt 5.13 | Qt QML | C++ Classes | QQmlListProperty

Qt 5.13.2 Reference Documentation

# QQmlListProperty Class

The QQmlListProperty class allows applications to expose list-like properties of QObject-derived classes to QML. More...

Header: | #include <QQmlListProperty>
qmake: | QT += qml
Since: | Qt 5.0

This class was introduced in Qt 5.0.

- List of all members, including inherited members

## Public Types

typedef | AppendFunction
typedef | AtFunction
typedef | ClearFunction
typedef | CountFunction

## Public Functions

| QQmlListProperty(QObject *object, void *data, QQmlListProperty::CountFunction count, QQmlListProperty::AtFunction at)
| QQmlListProperty(QObject *object, void *data, QQmlListProperty::AppendFunction append, QQmlListProperty::CountFunction count, QQmlListProperty::AtFunction at, QQmlListProperty::ClearFunction clear)
| QQmlListProperty(QObject *object, int &list)
bool | operator==(const QQmlListProperty<T> &other) const

## Detailed Description

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:

      FruitBasket {
          fruit: [
              Apple {},
              Orange{},
              Banana{}
          ]
      }

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:

      Q_PROPERTY(QQmlListProperty<Fruit> fruit READ fruit)

QML list properties are type-safe - in this case `Fruit` is a QObject type that `Apple`, `Orange` and `Banana` all derive from.

See also Extending QML - Object and List Property Types Example.

## Member Type Documentation

### typedef QQmlListProperty::AppendFunction

Synonym for `void (*)(QQmlListProperty<T> *property, T *value)`.

Append the value to the list property.

### typedef QQmlListProperty::AtFunction

Synonym for `T *(*)(QQmlListProperty<T> *property, int index)`.

Return the element at position index in the list property.

### typedef QQmlListProperty::ClearFunction

Synonym for `void (*)(QQmlListProperty<T> *property)`.

Clear the list property.

### typedef QQmlListProperty::CountFunction

Synonym for `int (*)(QQmlListProperty<T> *property)`.

Return the number of elements in the list property.

## Member Function Documentation

### QQmlListProperty::QQmlListProperty(QObject *object, void *data, QQmlListProperty::CountFunction count, QQmlListProperty::AtFunction at)

Construct a readonly QQmlListProperty from a set of operation functions count and at. An opaque data handle may be passed which can be accessed from within the operation functions. The list property remains valid while object exists.

### QQmlListProperty::QQmlListProperty(QObject *object, void *data, QQmlListProperty::AppendFunction append, QQmlListProperty::CountFunction count, QQmlListProperty::AtFunction at, QQmlListProperty::ClearFunction clear)

Construct a QQmlListProperty from a set of operation functions append, count, at, and clear. An opaque data handle may be passed which can be accessed from within the operation functions. The list property remains valid while object 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.

### QQmlListProperty::QQmlListProperty(QObject *object, int &list)

Convenience constructor for making a QQmlListProperty value from an existing QList list. The list reference must remain valid for as long as object exists. object must be provided.

Generally this constructor should not be used in production code, as a writable QList violates QML's memory management rules. However, this constructor can be very useful while prototyping.

### bool QQmlListProperty::operator==(const QQmlListProperty<T> &other) const

Returns true if this QQmlListProperty is equal to other, otherwise false.