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The QObject class is the base class of all Qt objects. More...
#include <qobject.h>
Inherits Qt.
Inherited by QAccel, QAction, QApplication, QAuServer, QCanvas, QClipboard, QDataPump, QDns, QDnsSocket, QDragManager, QDragObject, QFileIconProvider, QGuardedPtrPrivate, QLayout, QNPInstance, QNetworkOperation, QNetworkProtocol, QSenderObject, QServerSocket, QSessionManager, QSignal, QSignalMapper, QSocket, QSocketNotifier, QSound, QStyle, QStyleSheet, QTimer, QToolTipGroup, QTranslator, QUrlOperator, QValidator, QWSManager and QWidget.
| Type | Name | READ | WRITE | Options |
|---|---|---|---|---|
| QCString | name | name | setName |
QObject is the heart of the Qt object model. The central feature in this model is a very powerful mechanism for seamless object commuinication dubbed signals and slots. With connect(), you can connect a signal to a slot and destroy the connection again with disconnect(). To avoid never-ending notification loops, you can temporarily block signals with blockSignals(). The protected functions connectNotify() and disconnectNotify() make it possible to track connections.
QObjects organize themselves in object trees. When you create a QObject with another object as parent, it will automatically do an insertChild() on the parent and thus show up in the parent's children() list. The parent receives object ownership, i.e. it will automatically delete its children in its destructor. You can look for an object by name and optionally type using child() or queryList(), and get the list of tree roots using objectTrees().
Every object has an object name() and can report its className() and whether it inherits() another class in the QObject inheritance hierarchy.
When an object is deleted, it emits a destroyed() signal. You can catch this signal to avoid dangling references to QObjects. The QGuardedPtr class provides an elegant way to use this feature.
QObjects can receive events through event() and filter events of other objects. See installEventFilter() and eventFilter() for details. A convenience handler childEvent() can be reimplemented to catch child events.
Last but not least, QObject provides the basic timer support in Qt, see QTimer for high-level support for timers.
Notice that the Q_OBJECT macro is mandatory for any object that
implement signals, slots or properties. You also need to run the
moc program (Meta Object Compiler) on the
source file. We strongly recommend to use the macro in all
subclasses of QObject regardless whether they actually use signals,
slots and properties or not. Otherwise certain functions can show
undefined behaviour.
All Qt widgets inherit QObject. The convenience function isWidgetType() returns whether an object is actually a widget. It is much faster than inherits( "QWidget" ).
Constructs an object with the parent object parent and a name.
The parent of an object may be viewed as the object's owner. For instance, a dialog box is the parent of the "ok" and "cancel" buttons inside it.
The destructor of a parent object destroys all child objects.
Setting parent to 0 constructs an object with no parent. If the object is a widget, it will become a top-level window.
The object name is a text that can be used to identify this QObject. It's particularly useful in conjunction with the Qt Designer. You can find an object by name (and type) using child(), and more than one using queryList().
See also parent(), name(), child() and queryList().
[virtual]Destructs the object, deleting all its child objects.
All signals to and from the object are automatically disconnected.
Warning: All child objects are deleted. If any of these objects are on the stack or global, your program will sooner or later crash. We do not recommend holding pointers to child objects from outside the parent. If you still do, the QObject::destroyed() signal gives you an opportunity to detect when an object is destroyed.
[protected]This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.
[protected]This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.
[protected]This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.
[protected]This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.
[protected]For internal use only.
[protected]For internal use only.
[protected]For internal use only.
[static protected]Internal function, called from initMetaObject(). Used to emit a warning when a class containing the macro Q_OBJECT inherits from a class that does not contain it.
Blocks signals if block is TRUE, or unblocks signals if block is FALSE.
Emitted signals disappear into hyperspace if signals are blocked.
[virtual protected]Returns TRUE if the signal and the member arguments are compatible, otherwise FALSE.
Warning: We recommend that you do not reimplement this function but use the default implementation.
Searches through the children and grandchildren of this object for an object named name and with type type (or a subclass of that type), and returns a pointer to that object if it exists. If type is 0, any type matches.
If there isn't any such object, this function returns null.
If there is more than one, one of them is retured; use queryList() if you need all of them.
[virtual protected]This event handler can be reimplemented in a subclass to receive child events.
Child events are sent to objects when children are inserted or removed.
Note that events with QEvent::type() QEvent::ChildInserted are
posted (with QApplication::postEvent()), to make sure that the
child's construction is completed before this function is called.
If you change state based on ChildInserted events, call
QWidget::constPolish(), or do
QApplication::sendPostedEvents( this, QEvent::ChildInserted );
in functions that depend on the state. One notable example is
QWidget::sizeHint().
See also event() and QChildEvent.
Reimplemented in QWidgetStack, QGroupBox, QMainWindow, QWorkspace and QSplitter.
Returns a list of child objects, or 0 if this object has no children.
The QObjectList class is defined in the qobjcoll.h header file.
The latest child added is the first object in the list and the first child added is the last object in the list.
Note that the list order changes when QWidget children are raised or lowered. A widget that is raised becomes the last object in the list, and a widget that is lowered becomes the first object in the list.
See also child(), queryList(), parent(), insertChild() and removeChild().
[virtual]Returns the class name of this object.
This function is generated by the Meta Object Compiler.
Warning: This function will return an invalid name if the class
definition lacks the Q_OBJECT macro.
See also name(), inherits(), isA() and isWidgetType().
[static]Connects signal from the sender object to member in object receiver.
You must use the SIGNAL() and SLOT() macros when specifying the signal and the member.
Example:
QLabel *label = new QLabel;
QScrollBar *scroll = new QScrollBar;
QObject::connect( scroll, SIGNAL(valueChanged(int)),
label, SLOT(setNum(int)) );
This example connects the scroll bar's valueChanged() signal to the label's setNum() slot. It makes the label always display the current scroll bar value.
A signal can even be connected to another signal, i.e. member is a SIGNAL().
class MyWidget : public QWidget
{
public:
MyWidget();
...
signals:
void aSignal();
...
private:
...
QPushButton *aButton;
};
MyWidget::MyWidget()
{
aButton = new QPushButton( this );
connect( aButton, SIGNAL(clicked()), SIGNAL(aSignal()) );
}
In its constructor, MyWidget creates a private button and connects the clicked() signal to relay clicked() to the outside world. You can achieve the same effect by connecting the clicked() signal to a private slot and emitting aSignal() in this slot, but that takes a few lines of extra code and is not quite as clear, of course.
A signal can be connected to many slots/signals. Many signals can be connected to one slot.
If a signal is connected to several slots, the slots are activated in arbitrary order when the signal is emitted.
See also disconnect().
Examples: showimg/main.cpp action/main.cpp iconview/main.cpp grapher/grapher.cpp xform/xform.cpp application/main.cpp helpviewer/main.cpp i18n/main.cpp drawdemo/drawdemo.cpp popup/popup.cpp menu/menu.cpp qmag/qmag.cpp qwerty/main.cpp forever/forever.cpp rot13/rot13.cpp scrollview/scrollview.cpp addressbook/main.cpp movies/main.cpp hello/main.cpp customlayout/main.cpp mdi/main.cpp
This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.
Connects signal from the sender object to member in this object.
Equivalent to: QObject::connect(sender, signal, this, member).
See also disconnect().
[virtual protected]This virtual function is called when something has been connected to signal in this object.
Warning: This function violates the object-oriented principle of modularity. However, it might be useful when you need to perform expensive initialization only if something is connected to a signal.
See also connect() and disconnectNotify().
Reimplemented in QClipboard.
[signal]This signal is emitted immediately before the object is destroyed.
All the objects's children are destroyed immediately after this signal is emitted.
[static]Disconnects signal in object sender from member in object receiver.
A signal-slot connection is removed when either of the objects involved are destroyed.
disconnect() is typically used in three ways, as the following examples show.
disconnect( myObject, 0, 0, 0 );
equivalent to the non-static overloaded function
myObject->disconnect();
disconnect( myObject, SIGNAL(mySignal()), 0, 0 );
equivalent to the non-static overloaded function
myObject->disconnect( SIGNAL(mySignal()) );
disconnect( myObject, 0, myReceiver, 0 );
equivalent to the non-static overloaded function
myObject->disconnect( myReceiver );
0 may be used as a wildcard, meaning "any signal", "any receiving object" or "any slot in the receiving object" respectively.
The sender may never be 0. (You cannot disconnect signals from more than one object.)
If signal is 0, it disconnects receiver and member from any signal. If not, only the specified signal is disconnected.
If receiver is 0, it disconnects anything connected to signal. If not, slots in objects other than receiver are not disconnected.
If member is 0, it disconnects anything that is connected to receiver. If not, only slots named member will be disconnected, and all other slots are left alone. The member must be 0 if receiver is left out, so you cannot disconnect a specifically-named slot on all objects.
See also connect().
This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.
Disconnects all signals in this object from member of receiver.
A signal-slot connection is removed when either of the objects involved are destroyed.
This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.
Disconnects signal from member of receiver.
A signal-slot connection is removed when either of the objects involved are destroyed.
[virtual protected]This virtual function is called when something has been disconnected from signal in this object.
Warning: This function violates the object-oriented principle of modularity. However, it might be useful for optimizing access to expensive resources.
See also disconnect() and connectNotify().
Dumps information about signal connections etc. for this object to the debug output.
This function is useful for debugging. This function does nothing if the library has been compiled in release mode (i.e without debugging information).
Dumps a tree of children to the debug output.
This function is useful for debugging. This function does nothing if the library has been compiled in release mode (i.e without debugging information).
[virtual]This virtual function receives events to an object and should return TRUE if the event was recognized and processed.
The event() function can be reimplemented to customize the behavior of an object.
See also installEventFilter(), timerEvent(), QApplication::sendEvent(), QApplication::postEvent() and QWidget::event().
Reimplemented in QSplitter, QToolBar, QClipboard, QSocketNotifier, QStatusBar, QMainWindow, QLineEdit, QGroupBox, QTimer, QMultiLineEdit and QWidget.
[virtual]Filters events if this object has been installed as an event filter for another object.
The reimplementation of this virtual function must return TRUE if the event should be stopped, or FALSE if the event should be dispatched normally.
Warning: If you delete the receiver object in this function, be sure to return TRUE. If you return FALSE, Qt sends the event to the deleted object and the program will crash.
See also installEventFilter().
Reimplemented in QScrollView, QToolBar, QMainWindow, QTabWidget, QFontDialog, QFileDialog, QSpinBox, QLayout, QSGIStyle, QAccel, QListView, QComboBox, QTable, QWorkspace, QMotifPlusStyle, QIconView, QMenuBar and QWizard.
Returns TRUE if the object is a high priority object, or FALSE if it is a standard priority object.
High priority objects are placed first in list of children, on the assumption that they will be referenced very often.
Returns TRUE if this object is an instance of a class that inherits clname, and clname inherits QObject.
(A class is considered to inherit itself.)
Example:
QTimer *t = new QTimer; // QTimer inherits QObject
t->inherits("QTimer"); // returns TRUE
t->inherits("QObject"); // returns TRUE
t->inherits("QButton"); // returns FALSE
QScrollBar * s = new QScrollBar; // inherits QWidget and QRangeControl
s->inherits( "QWidget" ); // returns TRUE
s->inherits( "QRangeControl" ); // returns FALSE
See also isA() and metaObject().
[virtual protected]Initializes the meta object of this object. This method is automatically executed on demand.
See also metaObject().
[virtual]Inserts an object obj into the list of child objects.
Warning: This function cannot be used to make a widget a child widget of another. Child widgets can be created only by setting the parent widget in the constructor or by calling QWidget::reparent().
See also removeChild() and QWidget::reparent().
Installs an event filter obj for this object.
An event filter is an object that receives all events that are sent to this object. The filter can either stop the event or forward it to this object. The event filter obj receives events via its eventFilter() function. The eventFilter() function must return TRUE if the event should be stopped, or FALSE if the event should be dispatched normally.
If multiple event filters are installed for a single object, the filter that was installed last is activated first.
Example:
#include <qwidget.h>
class MyWidget : public QWidget
{
public:
MyWidget::MyWidget( QWidget *parent=0, const char *name=0 );
protected:
bool eventFilter( QObject *, QEvent * );
};
MyWidget::MyWidget( QWidget *parent, const char *name )
: QWidget( parent, name )
{
if ( parent ) // has a parent widget
parent->installEventFilter( this ); // then install filter
}
bool MyWidget::eventFilter( QObject *o, QEvent *e )
{
if ( e->type() == QEvent::KeyPress ) { // key press
QKeyEvent *k = (QKeyEvent*)e;
qDebug( "Ate key press %d", k->key() );
return TRUE; // eat event
}
return QWidget::eventFilter( o, e ); // standard event processing
}
The QAccel class, for example, uses this technique.
Warning: If you delete the receiver object in your eventFilter() function, be sure to return TRUE. If you return FALSE, Qt sends the event to the deleted object and the program will crash.
See also removeEventFilter(), eventFilter() and event().
Returns TRUE if this object is an instance of a specified class, otherwise FALSE.
Example:
QTimer *t = new QTimer; // QTimer inherits QObject
t->isA("QTimer"); // returns TRUE
t->isA("QObject"); // returns FALSE
See also inherits() and metaObject().
Returns TRUE if the object is a widget, or FALSE if not.
Calling this function is equivalent to calling inherits("QWidget"), except that it is much faster.
Kills the timer with the identifier id.
The timer identifier is returned by startTimer() when a timer event is started.
See also timerEvent(), startTimer() and killTimers().
Examples: grapher/grapher.cpp
Kills all timers that this object has started.
Note that using this function can cause hard-to-find bugs: It kills timers started by sub- and superclasses as well as those started by you, which is often not what you want. Therefore, we recommend using a QTimer, or perhaps killTimer().
See also timerEvent(), startTimer() and killTimer().
Examples: xform/xform.cpp qmag/qmag.cpp
[virtual]Returns a pointer to the meta object of this object.
A meta object contains information about a class that inherits
QObject: class name, super class name, properties, signals and
slots. Every class that contains the Q_OBJECT macro will also
have a meta object.
The meta object information is required by the signal/slot connection mechanism and the property system. The functions isA() and inherits() also make use of the meta object.
Returns the name of this object. If the object does not have a name, it will return "unnamed", so that printf() (used in qDebug()) will not be asked to output a null pointer. If you want a null pointer to be returned for unnamed objects, you can call name( 0 ).
qDebug( "MyClass::setPrecision(): (%s) unable to set precision to %f",
name(), newPrecision );
The object name is set by the constructor or by the setName() function. The object name is not very useful in the current version of Qt, but will become increasingly important in the future.
You can find an object by name (and type) using child(), and more than one using queryList().
See also setName(), className(), child() and queryList().
Returns the name of this object, or defaultName if the object does not have a name.
[static protected]Normlizes the signal or slot definition signalSlot by removing unnecessary whitespaces.
[static]Returns a pointer to the list of all object trees (respectively their root objects), or 0 if there are no objects.
The QObjectList class is defined in the qobjcoll.h header file.
The latest root object created is the first object in the list and the first root object added is the last object in the list.
See also children(), parent(), insertChild() and removeChild().
Returns a pointer to the parent object.
See also children().
Returns the value of the object's name property.
If no such property exists, the returned variant is invalid.
Information about all available properties are provided through the metaObject().
See also setProperty(), QVariant::isValid(), metaObject(), QMetaObject::propertyNames() and QMetaObject::property().
Searches the children and optinally grandchildren of this object, and returns a list of those objects that are named or matches objName and inherit ineritsClass. If inheritsClass is 0 (the default), all classes match. IF objName is 0 (the default), all object names match.
If regexpMatch is TRUE (the default), objName is a regexp that the objects's names must match. If regexpMatch is FALSE, objName is a string and object names must match it exactly.
Note that ineritsClass uses single inheritance from QObject, the way inherits() does. According to inherits(), QMenuBar inherits QWidget but not QMenuData. This does not quite match reality, but is the best that can be done on the wide variety of compilers Qt supports.
Finally, if recursiveSearch is TRUE (the default), queryList() searches nth-generation as well as first-generation children.
If all this seems a bit complex for your needs, the simpler function child() may be what you want.
This somewhat contrived example disables all the buttons in this window:
QObjectList * l = topLevelWidget()->queryList( "QButton" );
QObjectListIt it( *l ); // iterate over the buttons
QObject * obj;
while ( (obj=it.current()) != 0 ) { // for each found object...
++it;
((QButton*)obj)->setEnabled( FALSE );
}
delete list; // delete the list, not the objects
Warning: Delete the list away as soon you have finished using it. The list contains pointers that may become invalid at almost any time without notice - as soon as the user closes a window you may have dangling pointers, for example.
See also child(), children(), parent(), inherits(), name() and QRegExp.
[protected]Returns a list of objects/slot pairs that are connected to the signal, or 0 if nothing is connected to it.
This function is for internal use.
[virtual]Removes the child object obj from the list of children.
Warning: This function will not remove a child widget from the screen. It will only remove it from the parent widget's list of children.
See also insertChild() and QWidget::reparent().
Reimplemented in QScrollView.
Removes an event filter object obj from this object. The request is ignored if such an event filter has not been installed.
All event filters for this object are automatically removed when this object is destroyed.
It is always safe to remove an event filter, even during event filter activation (i.e. from the eventFilter() function).
See also installEventFilter(), eventFilter() and event().
[protected]Returns a pointer to the object that sent the signal, if called in a slot before any function call or signal emission. Returns an undefined value in all other cases.
Warning: This function will return something apparently correct in other cases as well. However, its value may change during any function call, depending on what signal-slot connections are activated during that call. In Qt 3.0 the value will change more often than in 2.x.
Warning: This function violates the object-oriented principle of modularity, However, getting access to the sender might be practical when many signals are connected to a single slot. The sender is undefined if the slot is called as a normal C++ function.
[virtual]Sets the name of this object to name. The default name is the one assigned by the constructor.
You can find an object by name (and type) using child(), and more than one using queryList().
See also name(), className(), queryList() and child().
Reimplemented in QWidget and QSignal.
Sets the object's property name to value.
Returne TRUE is the operation was successful, FALSE otherwise.
Information about all available properties are provided through the metaObject().
See also property(), metaObject(), QMetaObject::propertyNames() and QMetaObject::property().
Returns TRUE if signals are blocked, or FALSE if signals are not blocked.
Signals are not blocked by default.
See also blockSignals().
Starts a timer and returns a timer identifier, or returns zero if it could not start a timer.
A timer event will occur every interval milliseconds until killTimer() or killTimers() is called. If interval is 0, then the timer event occurs once every time there are no more window system events to process.
The virtual timerEvent() function is called with the QTimerEvent event parameter class when a timer event occurs. Reimplement this function to get timer events.
If multiple timers are running, the QTimerEvent::timerId() can be used to find out which timer was activated.
Example:
class MyObject : public QObject
{
public:
MyObject( QObject *parent=0, const char *name=0 );
protected:
void timerEvent( QTimerEvent * );
};
MyObject::MyObject( QObject *parent, const char *name )
: QObject( parent, name )
{
startTimer( 50 ); // 50 millisecond timer
startTimer( 1000 ); // 1 second timer
startTimer( 60000 ); // 1 minute timer
}
void MyObject::timerEvent( QTimerEvent *e )
{
qDebug( "timer event, id=%d", e->timerId() );
}
There is practically no upper limit for the interval value (more than one year). The accuracy depends on the underlying operating system. Windows 95 has 55 millisecond (18.2 times per second) accuracy; other systems that we have tested (UNIX X11, Windows NT and OS/2) can handle 1 millisecond intervals.
The QTimer class provides a high-level programming interface with one-shot timers and timer signals instead of events.
See also timerEvent(), killTimer() and killTimers().
Examples: qmag/qmag.cpp forever/forever.cpp
[static protected]The functionality of initMetaObject(), provided as a static function.
This function is obsolete. It is provided to keep old source working, and will probably be removed in a future version of Qt. We strongly advise against using it in new code.
This function is misleadingly named, and cannot be implemented in a way that fulfills its name. someQWidget->superClasses() should have returned QPaintDevice and QObject, obviously. And it never can, so let us kill the function. It will be removed in Qt-3.0
Oh, and the return type was wrong, too. QStringList not QStrList.
[virtual protected]This event handler can be reimplemented in a subclass to receive timer events for the object.
QTimer provides a higher-level interface to the timer functionality, and also more general information about timers.
See also startTimer(), killTimer(), killTimers() and event().
Reimplemented in QPopupMenu and QMultiLineEdit.
[static]Returns a translated version of text in context QObject and and with comment, or text if there is no appropriate translated version. All QObject subclasses which use the Q_OBJECT macro have a reimplementation of this function which uses the relevant class name as context.
See also QApplication::translate().
[static]This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.
Returns a translated version of text in context QObject and with no comment, or text if there is no appropriate translated version. All QObject subclasses which use the Q_OBJECT macro have a reimplementation of this function which uses the relevant class name as context.
See also QApplication::translate().
[protected]For internal use only.
[protected]For internal use only.
Returns a pointer to the child named name of QObject parent which inherits type type.
Returns 0 if there is no such child.
QListBox * c = (QListBox *)::qt_find_obj_child(myWidget,QListBox,
"listboxname");
if ( c )
c->insertItem( "another string" );
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