QModelIndex Class Reference
[QtCore module]

Detailed Description

The QModelIndex class is used to locate data in a data model.

This class is used as an index into item models derived from QAbstractItemModel. The index is used by item views, delegates, and selection models to locate an item in the model.

New QModelIndex objects are created by the model using the QAbstractItemModel::createIndex() function. An invalid model index can be constructed with the QModelIndex constructor. Invalid indexes are often used as parent indexes when referring to top-level items in a model.

Model indexes refer to items in models, and contain all the information required to specify their locations in those models. Each index is located in a given row and column, and may have a parent index; use row(), column(), and parent() to obtain this information. Each top-level item in a model is represented by a model index that does not have a parent index - in this case, parent() will return an invalid model index, equivalent to an index constructed with the zero argument form of the QModelIndex() constructor.

To obtain a model index that refers to an existing item in a model, call QAbstractItemModel::index() with the required row and column values, and the model index of the parent. When referring to top-level items in a model, supply QModelIndex() as the parent index.

The model() function returns the model that the index references as a QAbstractItemModel. The child() function is used to examine the items held beneath the index in the model. The sibling() function allows you to traverse items in the model on the same level as the index.

Note: Model indexes should be used immediately and then discarded. You should not rely on indexes to remain valid after calling model functions that change the structure of the model or delete items. If you need to keep a model index over time use a QPersistentModelIndex.

See also Model/View Programming, QPersistentModelIndex, and QAbstractItemModel.

Member Function Documentation

QModelIndex::QModelIndex ()

Creates a new empty model index. This type of model index is used to indicate that the position in the model is invalid.

See also isValid() and QAbstractItemModel.

QModelIndex::QModelIndex ( const QModelIndex & other )

Creates a new model index that is a copy of the other model index.

QModelIndex::~QModelIndex ()

Destroys the model index.

QModelIndex QModelIndex::child ( int row, int column ) const

Returns the child of the model index that is stored in the given row and column.

See also parent() and sibling().

int QModelIndex::column () const

Returns the column this model index refers to.

QVariant QModelIndex::data ( int role = Qt::DisplayRole ) const

Returns the data for the given role for the item referred to by the index.

Qt::ItemFlags QModelIndex::flags () const

Returns the flags for the item referred to by the index.

This function was introduced in Qt 4.2.

qint64 QModelIndex::internalId () const

Returns a qint64 used by the model to associate the index with the internal data structure.

See also QAbstractItemModel::createIndex().

void * QModelIndex::internalPointer () const

Returns a void * pointer used by the model to associate the index with the internal data structure.

See also QAbstractItemModel::createIndex().

bool QModelIndex::isValid () const

Returns true if this model index is valid; otherwise returns false. A valid index belongs to a model, and has non-negative row and column numbers.

See also model(), row(), and column().

const QAbstractItemModel * QModelIndex::model () const

Returns a pointer to the model containing the item that this index refers to.

You receive a const pointer to the model because calls to non-const functions of the model might invalidate the model index - and possibly crash your application.

QModelIndex QModelIndex::parent () const

Returns the parent of the model index, or QModelIndex() if it has no parent.

See also child(), sibling(), and model().

int QModelIndex::row () const

Returns the row this model index refers to.

QModelIndex QModelIndex::sibling ( int row, int column ) const

Returns the sibling at row and column or an invalid QModelIndex if there is no sibling at this position.

See also parent() and child().

bool QModelIndex::operator!= ( const QModelIndex & other ) const

Returns true if this model index does not refer to the same location as the other model index; otherwise returns false.

bool QModelIndex::operator< ( const QModelIndex & other ) const

Returns true if this model index is smaller than the other model index; otherwise returns false.

This function was introduced in Qt 4.1.

bool QModelIndex::operator== ( const QModelIndex & other ) const

Returns true if this model index refers to the same location as the other model index; otherwise returns false. Note that all values in the model index are used when comparing with another model index.

Related Non-Members

typedef QModelIndexList

Synonym for QList<QModelIndex>.