Qt 4.7: QDeclarativeListProperty Class Reference

Qt Reference Documentation

# QDeclarativeListProperty Class Reference

The QDeclarativeListProperty class allows applications to expose list-like properties to QML. More...

     #include <QDeclarativeListProperty>

This class was introduced in Qt 4.7.

- List of all members, including inherited members

## Public Types

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

## Public Functions

| QDeclarativeListProperty ( QObject * object, QList<T *> & list )
| QDeclarativeListProperty ( QObject * object, void * data, AppendFunction append, CountFunction count = 0, AtFunction at = 0, ClearFunction clear = 0 )
bool | operator== ( const QDeclarativeListProperty & other ) const

## Detailed Description

The QDeclarativeListProperty class allows applications to expose list-like properties 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:

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

The QDeclarativeListProperty encapsulates a group of function pointers that represet 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 QDeclarativeListProperty 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(QDeclarativeListProperty<Fruit> fruit READ fruit);

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

Note: QDeclarativeListProperty can only be used for lists of QObject-derived object pointers.

See also Object and List Property Types.

## Member Type Documentation

### typedef QDeclarativeListProperty::AppendFunction

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

Append the value to the list property.

### typedef QDeclarativeListProperty::AtFunction

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

Return the element at position index in the list property.

### typedef QDeclarativeListProperty::ClearFunction

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

Clear the list property.

### typedef QDeclarativeListProperty::CountFunction

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

Return the number of elements in the list property.

## Member Function Documentation

### QDeclarativeListProperty::QDeclarativeListProperty ( QObject * object, QList<T *> & list )

Convenience constructor for making a QDeclarativeListProperty 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 very useful while prototyping.

### QDeclarativeListProperty::QDeclarativeListProperty ( QObject * object, void * data, AppendFunction append, CountFunction count = 0, AtFunction at = 0, ClearFunction clear = 0 )

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

The append operation is compulsory and must be provided, while the count, at and clear methods are optional.

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

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