This tutorial covers basic usage of widgets and layouts, showing how they are used to build GUI applications.
Widgets are the basic building blocks for graphical user interface (GUI) applications built with Qt. Each GUI component (e.g. buttons, labels, text editors) is a
widgetthat is placed somewhere within a user interface window, or is displayed as an independent window. Each type of widget is provided by a subclass of
QWidget, which is itself a subclass of
QWidgetis not an abstract class. It can be used as a container for other widgets, and it can be subclassed with minimal effort to create new, custom widgets.
QWidgetis often used to create a window inside which other
QWidgets are placed.
QWidgets can be created with parent objects to indicate ownership, ensuring that objects are deleted when they are no longer used. With widgets, these parent-child relationships have an additional meaning: each child widget is displayed within the screen area occupied by its parent widget. This means that when you delete a window widget, all the child widgets it contains are also deleted.
Writing a Main Function¶
Many of the GUI examples provided with Qt follow the pattern of having a
main.cppfile, which contains the standard code to initialize the application, plus any number of other source/header files that contain the application logic and custom GUI components.
main.cpplooks like this:import sys from PySide2.QtWidgets import QApplication # Include header files for application components. # ... if __name__ == "__main__": app = QApplication(sys.argv) # Set up and show widgets. # ... sys.exit(app.exec_()) }
QApplicationobject is constructed, which can be configured with arguments passed in from the command line. After the widgets have been created and shown,
exec()is called to start Qt’s event loop. Control passes to Qt until this function returns. Finally,
main()returns the value returned by
Simple Widget Examples¶
Each of theses simple widget examples is written entirely within the
Real World Widget Examples¶
In these more advanced examples , the code that creates the widgets and layouts is stored in other files. For example, the GUI for a main window may be created in the constructor of a
Building The Examples¶
If you installed a binary package to get Qt, or if you compiled Qt yourself, the examples described in this tutorial should already be built and ready to run. If you wish to modify and recompile them, follow these steps:
From a command prompt, enter the directory containing the example you have modified.
qmakeand press Return. If this doesn’t work, make sure that the executable is on your path, or enter its full location.
On Linux/Unix and macOS, type
makeand press Return; on Windows with Visual Studio, type
nmakeand press Return.
An executable file is created in the current directory. On Windows, this file may be located in a
releasesubdirectory. You can run this executable to see the example code at work.
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