Qt 4.8: QDeclarativeListReference Class Reference

Qt Reference Documentation

# QDeclarativeListReference Class Reference

The QDeclarativeListReference class allows the manipulation of QDeclarativeListProperty properties. More...

     #include <QDeclarativeListReference>

This class was introduced in Qt 4.7.

- List of all members, including inherited members

## Public Functions

| QDeclarativeListReference ()
| QDeclarativeListReference ( QObject * object, const char * property, QDeclarativeEngine * engine = 0 )
bool | append ( QObject * object ) const
QObject * | at ( int index ) const
bool | canAppend () const
bool | canAt () const
bool | canClear () const
bool | canCount () const
bool | clear () const
int | count () const
bool | isValid () const
const QMetaObject * | listElementType () const
QObject * | object () const

## Detailed Description

The QDeclarativeListReference class allows the manipulation of QDeclarativeListProperty properties.

QDeclarativeListReference allows C++ programs to read from, and assign values to a QML list property in a simple and type safe way. A QDeclarativeListReference can be created by passing an object and property name or through a QDeclarativeProperty instance. These two are equivalant:

     QDeclarativeListReference ref1(object, "children");

     QDeclarativeProperty ref2(object, "children");
     QDeclarativeListReference ref2 = qvariant_cast<QDeclarativeListReference>(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 typesafe. 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

### QDeclarativeListReference::QDeclarativeListReference ()

Constructs an invalid instance.

### QDeclarativeListReference::QDeclarativeListReference ( QObject * object, const char * property, QDeclarativeEngine * engine = 0 )

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

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

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

See also canAppend().

### QObject * QDeclarativeListReference::at ( int index ) const

Returns the list element at index, or 0 if the operation failed.

See also canAt().

### bool QDeclarativeListReference::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 QDeclarativeListReference::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 QDeclarativeListReference::canClear () const

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

See also clear().

### bool QDeclarativeListReference::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 QDeclarativeListReference::clear () const

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

See also canClear().

### int QDeclarativeListReference::count () const

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

### bool QDeclarativeListReference::isValid () const

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

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

Returns the QMetaObject for the elements stored in the list property. Returns 0 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 * QDeclarativeListReference::object () const

Returns the list property's object. Returns 0 if the reference is invalid.