Signals and Slots


The slot is a rectangular area in field hockey and ice hockey that extends toward the blue line. It is also the fourth position on a flying display. The word slot is related to the German word Schloss. It is also cognate with the verb sleutana, which means “to shoot.”


Signals and slots are Qt language constructs that communicate between objects. They make implementing the observer pattern incredibly easy and avoid boilerplate code. They are also a great way to make Qt code maintainable. Learn more about the different types of signals and slots, and how to use them in your Qt applications.

When calling a signal from a signal object, you can specify which slot should respond to the signal. The signal object will read the slot’s parameter and then decide whether or not to execute code. However, you must note that each slot needs to respond to a different value every time it is called. This means that the same signal can’t be used twice.

Signal and slot member functions are defined with the Q_OBJECT macro. The slot and signal member functions are then invoked by the Meta Object Compiler, which writes code for them. Creating a signal and slot object is simple, but you should be aware of the limitations. Slot signals are not supported by all signal implementations, and signal-slot connections cannot be overloaded.

Some signal libraries require a reference to the signal. Others enable keeping the connection even after the signal is destroyed. Generally, slot signal calls return a CYISignalConnectionID object, which should be retained by the user. The corresponding signal handlers can be copied by using the copy() method.

In Qt, there are many predefined signals and slots. However, you can also add your own slots and signals using the subclassing mechanism. The slots and signals mechanism is designed to be type-safe. That means you don’t have to worry about extra arguments and the wildcard void* type. You can also ignore any additional arguments if necessary.

Slot signals are a useful Qt language construct. They make implementing the observer pattern easy, and can be used to avoid boilerplate code. They are both public access functions and can be emitted by any object. It’s best to use a class that defines the signal in its definition, and to avoid using a signal defined by a subclass of QObject.

Slot signals are used to send and receive data. For example, a cell may receive data in slot three at 935 MHz (GSM) or on an 1880 MHz DCS channel. The Rx signal from slots two and three is downconverted to the IF1 frequency of 400 MHz (Load). Another signal is mixed with the fixed-frequency signal from slot two. The combined signal is produced at 1480 MHz by the mixer.