Q3Signal Class

The Q3Signal class can be used to send signals for classes that don't inherit QObject. More...

Header: #include <Q3Signal>
Inherits: QObject

Public Functions

Q3Signal(QObject * parent = 0, const char * name = 0)
void activate()
bool connect(const QObject * receiver, const char * member)
bool disconnect(const QObject * receiver, const char * member = 0)
void setValue(const QVariant & value)
QVariant value() const
  • 29 public functions inherited from QObject

Additional Inherited Members

  • 1 property inherited from QObject
  • 1 public slot inherited from QObject
  • 1 signal inherited from QObject
  • 7 static public members inherited from QObject
  • 8 protected functions inherited from QObject

Detailed Description

The Q3Signal class can be used to send signals for classes that don't inherit QObject.

If you want to send signals from a class that does not inherit QObject, you can create an internal Q3Signal object to emit the signal. You must also provide a function that connects the signal to an outside object slot. This is how we used to implement signals in Qt 3's QMenuData class, which was not a QObject. In Qt 4, menus contain actions, which are QObjects.

In general, we recommend inheriting QObject instead. QObject provides much more functionality.

You can set a single QVariant parameter for the signal with setValue().

Note that QObject is a private base class of Q3Signal, i.e. you cannot call any QObject member functions from a Q3Signal object.


#include <q3signal.h>

class MyClass

    void doSomething();

    void connect(QObject *receiver, const char *member);

    Q3Signal *sig;

    sig = new Q3Signal;

    delete sig;

void MyClass::doSomething()
    // ... does something
    sig->activate(); // emits the signal

void MyClass::connect(QObject *receiver, const char *member)
    sig->connect(receiver, member);

Member Function Documentation

Q3Signal::Q3Signal(QObject * parent = 0, const char * name = 0)

Constructs a signal object called name, with the parent object parent. These arguments are passed directly to QObject.


Destroys the signal. All connections are removed, as is the case with all QObjects.

void Q3Signal::activate()

Emits the signal. If the platform supports QVariant and a parameter has been set with setValue(), this value is passed in the signal.

bool Q3Signal::connect(const QObject * receiver, const char * member)

Connects the signal to member in object receiver. Returns true if the connection is successful.

See also disconnect() and QObject::connect().

bool Q3Signal::disconnect(const QObject * receiver, const char * member = 0)

Disonnects the signal from member in object receiver. Returns true if the connection existed and the disconnect was successful.

See also connect() and QObject::disconnect().

void Q3Signal::setValue(const QVariant & value)

Sets the signal's parameter to value

See also value().

QVariant Q3Signal::value() const

Returns the signal's parameter

See also setValue().

© 2016 The Qt Company Ltd. Documentation contributions included herein are the copyrights of their respective owners. The documentation provided herein is licensed under the terms of the GNU Free Documentation License version 1.3 as published by the Free Software Foundation. Qt and respective logos are trademarks of The Qt Company Ltd. in Finland and/or other countries worldwide. All other trademarks are property of their respective owners.