Signals and slots is a language construct introduced also in Qt[1] for communication between objects which makes it easy to implement the observer pattern while avoiding boilerplate code. The concept is that GUI widgets can send signals containing event information which can be received by other widgets / controls using special functions known as slots. This is similar to C/C++ function pointers, but signal/slot system ensures the type-correctness of callback arguments.[citation needed]
Hi, first let me introduce the programm situation: The programm connects to an TCPIP Server, and it launches its own TCPIP Server, where a client connects to. From the connected Server, the programm receives Info-Lines, which are written in a txt-file, th. Detailed Description. 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. Signals and slots are used for communication between objects. The signals and slots mechanism is a central feature of Qt. In GUI programming, when we change one widget, we often want another widget to be notified. More generally, we want objects of any kind to be able to communicate with one another.
The signal/slot system fits well with the way graphical user interfaces are designed.[citation needed] Similarly, the signal/slot system can be used for other non-GUI usages, for example asynchronous I/O (including sockets, pipes, serial devices, etc.) event notification or to associate timeout events with appropriate object instances and methods or functions. It is easy to use and no registration/deregistration/invocation code need to be written, because Qt's metaobject compiler (MOC) automatically generates the needed infrastructure.
Further properties of signal/slots. Qt provides the QObject::sender function, which returns a pointer to the object that sent the signal Note: if the slot was not activated by a signal, the return is undefined. Signals and slots are loosely coupled: A class which emits a signal neither knows nor cares which slots receive the signal. Qt will indeed call directly the function pointer of the slot, and will not need moc introspection anymore. (It still needs it for the signal) (It still needs it for the signal) But what we can also do is connecting to any function or functor.
A commonly used metaphor[according to whom?] is a spreadsheet. A spreadsheet has cells that observe the source cell(s). When the source cell is changed, the dependent cells are updated from the event.
Alternative implementations[edit]
There are some implementations of signal/slot systems based on C++ templates, which don't require the extra metaobject compiler, as used by Qt, such as libsigc++, sigslot, vdk-signals, nano-signal-slot, neosigslot, Signals, boost.signals2, Synapse, Cpp::Events, Platinum and JBroadcaster. Common Language Infrastructure (CLI) languages such as C# also supports a similar construct although with a different terminology and syntax: events play the role of signals, and delegates are the slots. Another implementation of signals exists for ActionScript 3.0, inspired by C# events and signals/slots in Qt. Additionally, a delegate can be a local variable, much like a function pointer, while a slot in Qt must be a class member declared as such. The C based GObject system also provides similar functionality via GSignal.In D it is implemented by std.signals.
See also[edit]
Libraries[edit]
Qt Signal And Slots
Java: sig4j - multi-threaded, type-safe, based on the FunctionalInterface annotation introduced in Java 8.
Qt Signal Slot Performance
C++: vdk-signals - thread-safe, type-safe, written in C++11 with atomic variables.
How Qt Signal And Slots Works
References[edit]
- ^'Signals & Slots - QtCore 5.1'. Qt Project. 2013-07-04. Retrieved 2013-07-04.
Qt Signal Slot Between Classes Chart
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