QQmlListReference Class
The QQmlListReference class allows the manipulation of QQmlListProperty properties. More...
| Header: | #include <QQmlListReference> |
| qmake: | QT += qml |
| Since: | Qt 5.0 |
Public Functions
| QQmlListReference() | |
| QQmlListReference(QObject *object, const char *property, QQmlEngine *engine = nullptr) | |
| 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 | isManipulable() const |
| bool | isReadable() const |
| bool | isValid() const |
| const QMetaObject * | listElementType() const |
| QObject * | object() const |
Detailed Description
The QQmlListReference class allows the manipulation of QQmlListProperty properties.
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()
Constructs an invalid instance.
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.
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(int 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::clear() const
Clears the list. Returns true if the operation succeeded, otherwise false.
See also canClear().
int 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 clear() are implemented, so you can manipulate the list.
See also isReadable(), at(), count(), append(), and clear().
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.
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