QApplication : Manages the control flow and main settings of a graphical interface application. All graphical user interface programs using QT have a QApplication object to provide message loop, event processing and other functions to ensure the program runs!
QObject : It is the root class of most classes in QT, and its structure is an object tree model. (QT’s object tree structure, in addition to defining the superior-subordinate relationship between components, can also use destructor order to solve memory problems.
QWidget : Inherited from QObject, it is the parent class of all components that can be displayed on the screen.
QPushButton : Button class, one of QT's common controls, inherited from QWidget, often dependent on the parent window.
QMainWindow : A class that provides users with the main window program, including a menu bar (menubar), multiple tool bars (tool bars), multiple dock widgets (dock widgets), a status bar (stats bar) and a central widget (central widget), which is the basis of many programs.
QDialog : Dialog box, usually a top-level window used to implement short-term tasks or indirect user interaction.
QLabel : used to display text, pictures, animations, etc. QLineEdit: Single-line text edit box.
Signal and slot mechanism:
Explanation: When an event occurs (signal), there is an object paying attention to this event.