com.trolltech.qt.core
Class QObject

java.lang.Object
  extended by com.trolltech.qt.internal.QSignalEmitterInternal
      extended by com.trolltech.qt.QSignalEmitter
          extended by com.trolltech.qt.QtJambiObject
              extended by com.trolltech.qt.core.QObject
All Implemented Interfaces:
QtJambiInterface
Direct Known Subclasses:
AbstractAudioOutput, Effect, MediaController, MediaObject, QAbstractEventDispatcher, QAbstractItemDelegate, QAbstractItemModel, QAbstractMessageHandler, QAbstractNetworkCache, QAbstractTextDocumentLayout, QAbstractUriResolver, QAccessiblePlugin, QAction, QActionGroup, QButtonGroup, QClipboard, QCompleter, QCoreApplication, QDataWidgetMapper, QDrag, QEventLoop, QFileSystemWatcher, QFtp, QFutureWatcherBase, QGraphicsItemAnimation, QGraphicsScene, QGraphicsSvgItem, QGraphicsTextItem, QGraphicsWidget, QHttp, QIconEnginePluginV2, QImageIOPlugin, QInputContext, QInputContextPlugin, QIODevice, QItemSelectionModel, QLayout, QLocalServer, QMimeData, QMovie, QNetworkAccessManager, QNetworkCookieJar, QPictureFormatPlugin, QSessionManager, QSettings, QShortcut, QSignalMapper, QSocketNotifier, QSound, QSqlDriver, QStyle, QStylePlugin, QSvgRenderer, QSyntaxHighlighter, QSystemTrayIcon, QTcpServer, QTextCodecPlugin, QTextDocument, QTextObject, QTextObjectInterface, QThreadPool, QTimeLine, QTimer, QTranslator, QUndoGroup, QUndoStack, QValidator, QWebFrame, QWebHistoryInterface, QWebPage, QWebPluginFactory, QWidget

public class QObject
extends QtJambiObject

The QObject class is the base class of all Qt objects. QObject is the heart of the Qt object model. The central feature in this model is a very powerful mechanism for seamless object communication called signals and slots. You can connect a signal to a slot with connect() and destroy the connection 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, the object will automatically add itself to the parent's children() list. The parent takes ownership of the object i.e. it will automatically delete its children in its destructor. You can look for an object by name and optionally type using findChild() or findChildren().

Every object has an objectName() and its class name can be found via the corresponding metaObject() (see QMetaObject::className()). You can determine whether the object's class inherits another class in the QObject inheritance hierarchy by using the inherits() function.

When an object is deleted, it emits a destroyed() signal. You can catch this signal to avoid dangling references to QObjects.

QObjects can receive events through event() and filter the events of other objects. See installEventFilter() and eventFilter() for details. A convenience handler, childEvent(), can be reimplemented to catch child events.

Events are delivered in the thread in which the object was created; see Thread Support in Qt and thread() for details. Note that event processing is not done at all for QObjects with no thread affinity (thread() returns zero). Use the moveToThread() function to change the thread affinity for an object and its children (the object cannot be moved if it has a parent).

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 implements signals, slots or properties. You also need to run the Meta Object Compiler on the source file. We strongly recommend the use of this macro in all subclasses of QObject regardless of whether or not they actually use signals, slots and properties, since failure to do so may lead certain functions to exhibit strange behavior.

All Qt widgets inherit QObject. The convenience function isWidgetType() returns whether an object is actually a widget. It is much faster than qobject_cast<QWidget *>(obj) or obj->inherits("QWidget").

Some QObject functions, e.g. children(), return a QObjectList. QObjectList is a typedef for QList<QObject *>.

No copy constructor or assignment operator

QObject has neither a copy constructor nor an assignment operator. This is by design. Actually, they are declared, but in a private section with the macro Q_DISABLE_COPY(). In fact, all Qt classes derived from QObject (direct or indirect) use this macro to declare their copy constructor and assignment operator to be private. The reasoning is found in the discussion on Identity vs Value on the Qt Object Model page.

The main consequence is that you should use pointers to QObject (or to your QObject subclass) where you might otherwise be tempted to use your QObject subclass as a value. For example, without a copy constructor, you can't use a subclass of QObject as the value to be stored in one of the container classes. You must store pointers.

Auto-Connection

Qt's meta-object system provides a mechanism to automatically connect signals and slots between QObject subclasses and their children. As long as objects are defined with suitable object names, and slots follow a simple naming convention, this connection can be performed at run-time by the QMetaObject::connectSlotsByName() function.

uic generates code that invokes this function to enable auto-connection to be performed between widgets on forms created with Qt Designer. More information about using auto-connection with Qt Designer is given in the Using a Designer .ui File in Your Application section of the Qt Designer manual.

Dynamic Properties

From Qt 4.2, dynamic properties can be added to and removed from QObject instances at run-time. Dynamic properties do not need to be declared at compile-time, yet they provide the same advantages as static properties and are manipulated using the same API - using property() to read them and setProperty() to write them.

From Qt 4.3, dynamic properties are supported by Qt Designer, and both standard Qt widgets and user-created forms can be given dynamic properties.

{Object Trees and Object Ownership}

See also:
QMetaObject, QPointer, QObjectCleanupHandler, and Q_DISABLE_COPY().


Nested Class Summary
 
Nested classes/interfaces inherited from class com.trolltech.qt.QSignalEmitter
QSignalEmitter.AbstractSignal, QSignalEmitter.PrivateSignal0, QSignalEmitter.PrivateSignal1, QSignalEmitter.PrivateSignal2, QSignalEmitter.PrivateSignal3, QSignalEmitter.PrivateSignal4, QSignalEmitter.PrivateSignal5, QSignalEmitter.PrivateSignal6, QSignalEmitter.PrivateSignal7, QSignalEmitter.PrivateSignal8, QSignalEmitter.PrivateSignal9, QSignalEmitter.Signal0, QSignalEmitter.Signal1, QSignalEmitter.Signal2, QSignalEmitter.Signal3, QSignalEmitter.Signal4, QSignalEmitter.Signal5, QSignalEmitter.Signal6, QSignalEmitter.Signal7, QSignalEmitter.Signal8, QSignalEmitter.Signal9
 
Nested classes/interfaces inherited from class com.trolltech.qt.internal.QSignalEmitterInternal
com.trolltech.qt.internal.QSignalEmitterInternal.AbstractSignalInternal
 
Field Summary
 
Fields inherited from class com.trolltech.qt.internal.QSignalEmitterInternal
currentSender
 
Constructor Summary
QObject()
           
QObject(QObject parent)
           
 
Method Summary
protected  void childEvent(QChildEvent arg__1)
           
 java.util.List children()
           
 void connectSlotsByName()
          Searches recursively for all child objects of the given object, and connects matching signals from them to slots of object that follow the following form.
protected  void customEvent(QEvent arg__1)
           
 void disposeLater()
           
 void dumpObjectInfo()
           
 void dumpObjectTree()
           
 java.util.List dynamicPropertyNames()
           
 boolean event(QEvent arg__1)
           
 boolean eventFilter(QObject arg__1, QEvent arg__2)
           
 QObject findChild()
          Returns a child of this object, or 0 if there is no such object.
 QObject findChild(java.lang.Class cl)
          This functions searches for descendant(s) of this QObject.
 QObject findChild(java.lang.Class cl, java.lang.String name)
          This functions searches for descendant(s) of this QObject.
 java.util.List findChildren()
          Returns all children of this QObject, or an empty list if it has no children.
 java.util.List findChildren(java.lang.Class cl)
          This functions searches for descendant(s) of this QObject.
 java.util.List findChildren(java.lang.Class cl, QRegExp name)
          This functions searches for descendant(s) of this QObject.
 java.util.List findChildren(java.lang.Class cl, java.lang.String name)
          This functions searches for descendant(s) of this QObject.
 int indexOfProperty(java.lang.String name)
          Finds property name and returns its index; otherwise returns -1.
 void installEventFilter(QObject arg__1)
           
 boolean isWidgetType()
           
 void killTimer(int id)
           
 void moveToThread(java.lang.Thread thread)
           
 java.lang.String objectName()
           
 QObject parent()
           
 java.util.List properties()
          This functions searches for descendant(s) of this QObject.
 java.lang.Object property(java.lang.String name)
          Returns the value of the object's name property.
 void removeEventFilter(QObject arg__1)
           
 void setObjectName(java.lang.String name)
           
 void setParent(QObject arg__1)
           
 void setProperty(java.lang.String name, java.lang.Object value)
          Sets the value of the object's name property to value.
 int startTimer(int interval)
           
protected  void timerEvent(QTimerEvent arg__1)
           
 java.lang.String toString()
          Returns a string representation of the this QObject.
 QtProperty userProperty()
          Returns the property that has the USER flag set to true.
 
Methods inherited from class com.trolltech.qt.QtJambiObject
dispose, disposed, equals, finalize, reassignNativeResources, tr, tr, tr
 
Methods inherited from class com.trolltech.qt.QSignalEmitter
blockSignals, disconnect, disconnect, signalsBlocked, signalSender, thread
 
Methods inherited from class com.trolltech.qt.internal.QSignalEmitterInternal
__qt_signalInitialization
 
Methods inherited from class java.lang.Object
clone, getClass, hashCode, notify, notifyAll, wait, wait, wait
 
Methods inherited from interface com.trolltech.qt.QtJambiInterface
disableGarbageCollection, nativeId, nativePointer, reenableGarbageCollection, setJavaOwnership
 

Constructor Detail

QObject

public QObject()

QObject

public QObject(QObject parent)
Method Detail

children

public final java.util.List children()

disposeLater

public final void disposeLater()

dumpObjectInfo

public final void dumpObjectInfo()

dumpObjectTree

public final void dumpObjectTree()

dynamicPropertyNames

public final java.util.List dynamicPropertyNames()

installEventFilter

public final void installEventFilter(QObject arg__1)

isWidgetType

public final boolean isWidgetType()

killTimer

public final void killTimer(int id)

moveToThread

public final void moveToThread(java.lang.Thread thread)

objectName

public final java.lang.String objectName()

parent

public final QObject parent()

removeEventFilter

public final void removeEventFilter(QObject arg__1)

setObjectName

public final void setObjectName(java.lang.String name)

setParent

public final void setParent(QObject arg__1)

startTimer

public final int startTimer(int interval)

childEvent

protected void childEvent(QChildEvent arg__1)

customEvent

protected void customEvent(QEvent arg__1)

event

public boolean event(QEvent arg__1)

eventFilter

public boolean eventFilter(QObject arg__1,
                           QEvent arg__2)

timerEvent

protected void timerEvent(QTimerEvent arg__1)

findChildren

public final java.util.List findChildren()
Returns all children of this QObject, or an empty list if it has no children.


findChildren

public final java.util.List findChildren(java.lang.Class cl)
This functions searches for descendant(s) of this QObject.


findChildren

public final java.util.List findChildren(java.lang.Class cl,
                                         java.lang.String name)
This functions searches for descendant(s) of this QObject.


findChildren

public final java.util.List findChildren(java.lang.Class cl,
                                         QRegExp name)
This functions searches for descendant(s) of this QObject.


findChild

public final QObject findChild()
Returns a child of this object, or 0 if there is no such object. The search is performed recursively.

If there is more than one child matching the search, the most direct ancestor is returned. If there are several direct ancestors, it is undefined which one will be returned. In that case, findChildren() should be used.


findChild

public final QObject findChild(java.lang.Class cl)
This functions searches for descendant(s) of this QObject.


findChild

public final QObject findChild(java.lang.Class cl,
                               java.lang.String name)
This functions searches for descendant(s) of this QObject.


setProperty

public final void setProperty(java.lang.String name,
                              java.lang.Object value)
Sets the value of the object's name property to value.

If the property is defined in the class using Q_PROPERTY then true is returned on success and false otherwise. If the property is not defined using Q_PROPERTY, and therefore not listed in the meta-object, it is added as a dynamic property and false is returned.

Information about all available properties is provided through the metaObject() and dynamicPropertyNames().

Dynamic properties can be queried again using property() and can be removed by setting the property value to an invalid QVariant. Changing the value of a dynamic property causes a QDynamicPropertyChangeEvent to be sent to the object.

Note: Dynamic properties starting with "_q_" are reserved for internal purposes.


property

public final java.lang.Object property(java.lang.String name)
Returns the value of the object's name property.

If no such property exists, the returned object is invalid.

Information about all available properties is provided through the metaObject() and dynamicPropertyNames().


userProperty

public final QtProperty userProperty()
Returns the property that has the USER flag set to true.

See also:
QMetaProperty::isUser().


properties

public final java.util.List properties()
This functions searches for descendant(s) of this QObject.


indexOfProperty

public final int indexOfProperty(java.lang.String name)
Finds property name and returns its index; otherwise returns -1.


connectSlotsByName

public final void connectSlotsByName()
Searches recursively for all child objects of the given object, and connects matching signals from them to slots of object that follow the following form.

void on__();

Let's assume our object has a child object of type QPushButton with the object name button1. The slot to catch the button's clicked signal would be:

void on_button1_clicked()


toString

public java.lang.String toString()
Returns a string representation of the this QObject.

Overrides:
toString in class java.lang.Object