QPtrCollection Class Reference

Detailed Description

The QPtrCollection class is an abstract base class for the Qt collection classes QDict, QPtrList, etc. Qt also includes value based collections, e.g. QValueList, QMap, etc.

A QPtrCollection only knows about the number of objects in the collection and the deletion strategy (see setAutoDelete()).

A collection is implemented using the Item (generic collection item) type, which is a void*. The template classes that create the real collections cast the Item to the required type.

See also Collection Classes and Non-GUI Classes.

Member Type Documentation

QPtrCollection::Item

This type is the generic "item" in a QPtrCollection.

Member Function Documentation

QPtrCollection::QPtrCollection () [protected]

Constructs a collection. The constructor is protected because QPtrCollection is an abstract class.

QPtrCollection::QPtrCollection ( const QPtrCollection & source ) [protected]

Constructs a copy of source with autoDelete() set to FALSE. The constructor is protected because QPtrCollection is an abstract class.

Note that if source has autoDelete turned on, copying it will risk memory leaks, reading freed memory, or both.

QPtrCollection::~QPtrCollection () [virtual protected]

Destroys the collection. The destructor is protected because QPtrCollection is an abstract class.

bool QPtrCollection::autoDelete () const

Returns the setting of the auto-delete option. The default is FALSE.

See also setAutoDelete().

void QPtrCollection::clear () [pure virtual]

Removes all objects from the collection. The objects will be deleted if auto-delete has been enabled.

See also setAutoDelete().

Reimplemented in QAsciiDict, QCache, QDict, QIntDict, QPtrList, QPtrDict, and QPtrVector.

uint QPtrCollection::count () const [pure virtual]

Returns the number of objects in the collection.

Reimplemented in QAsciiDict, QCache, QDict, QIntDict, QPtrList, QPtrDict, and QPtrVector.

void QPtrCollection::deleteItem ( Item d ) [pure virtual protected]

Reimplement this function if you want to be able to delete items.

Deletes an item that is about to be removed from the collection.

This function has to reimplemented in the collection template classes, and should only delete item d if auto-delete has been enabled.

Warning: If you reimplement this function you must also reimplement the destructor and call the virtual function clear() from your destructor. This is due to the way virtual functions and destructors work in C++: Virtual functions in derived classes cannot be called from a destructor. If you do not do this, your deleteItem() function will not be called when the container is destroyed.

See also newItem() and setAutoDelete().

Item QPtrCollection::newItem ( Item d ) [virtual protected]

The default implementation returns the d pointer, i.e. no copy is made.

This function is seldom reimplemented in the collection template classes. It is not common practice to make a copy of something that is being inserted.

See also deleteItem().

void QPtrCollection::setAutoDelete ( bool enable )

Sets the collection to auto-delete its contents if enable is TRUE and to never delete them if enable is FALSE.

If auto-deleting is turned on, all the items in a collection are deleted when the collection itself is deleted. This is convenient if the collection has the only pointer to the items.

The default setting is FALSE, for safety. If you turn it on, be careful about copying the collection - you might find yourself with two collections deleting the same items.

Note that the auto-delete setting may also affect other functions in subclasses. For example, a subclass that has a remove() function will remove the item from its data structure, and if auto-delete is enabled, will also delete the item.

See also autoDelete().

Examples: grapher/grapher.cpp, scribble/scribble.cpp, and table/bigtable/main.cpp.

This file is part of the Qt toolkit. Copyright © 1995-2003 Trolltech. All Rights Reserved.