Qt working principle: event-driven, signal and slot mechanism
As a modern GUI (graphical user interface) framework, Qt adopts an event-driven programming paradigm and introduces signals and slot mechanisms to achieve highly interactive and loosely coupled programming. The relevant concepts and how to use them in Qt are explained in detail below.
Event
Events are various actions, operations or state changes that occur on controls in GUI applications, such as mouse movement, clicks, keyboard presses, control drawing, etc. Each control has an event handler function that captures and handles events related to the control.
Signal
Signal is an important concept in Qt. It is provided by the system class library or declared by the programmer himself, and is used to send messages when a specific event occurs. The signal is actually an incomplete function, only declared but not defined. For example, when the user clicks the button, the button control can send out a clicked signal.
Slot function
The slot function is a complete function, which is provided by the system class library or declared and defined by the programmer himself. It is used to respond to signals and implement specific functions. Slot functions can be declared in the public slots or private slots area of the class and defined within the class body. For example, when the clicked signal of a button is emitted, the slot function associated with it will be automatically called.
event driven
Event-driven means that the control flow in a GUI program is determined by the occurrence and processing of events. Whenever an event occurs, such as a mouse click on a button, a corresponding signal will be emitted, and then the slot function associated with the signal will be called to handle the event.
Signals and slots mechanism
The signal and slot mechanism is a way to implement communication between objects in Qt. By associating (binding, registering) a signal with one or more slot functions, the slot function can be automatically called to respond to the event when the signal is emitted. The system automatically calls the corresponding slot function to implement the function.
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