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We'll keep it simple and use just a single parent and a lone child.
public class FamilyValues { public static void main(String args[]) { QApplication.initialize(args); QWidget window = new QWidget(); window.resize(200, 120); QPushButton quit = new QPushButton("Quit", window); quit.setFont(new QFont("Times", 18, QFont.Weight.Bold.value())); quit.setGeometry(10, 40, 180, 40); quit.clicked.connect(QApplication.instance(), "quit()"); window.setWindowTitle("FamilyValues"); window.show(); QApplication.exec(); } }
QWidget window = new QWidget();Here we simply create a plain widget object. The QWidget class is the base class of all user interface objects. The widget is the atom of the user interface: It receives mouse, keyboard and other events from the window system, and paints a representation of itself on the screen. A widget is clipped by its parent and by the widgets in front of it.
A widget that isn't embedded in a parent widget, like this particular widget, is called a window. Usually, windows have their own window frame and taskbar entry, provided by the window system. A widget without a parent widget is always an independent window. Its initial position on the screen is controlled by the window system.
window.resize(200, 120);We set the window's width to 200 pixels and its height to 120 pixels.
QPushButton quit = new QPushButton("Quit", window);A child is born. This QPushButton is created with a parent widget (window). A child widget is always displayed within its parent's area. When displayed, it is clipped by its parent's bounds. By default, it is rooted at the top-left corner of its parent, at position (0, 0).
quit.setGeometry(10, 40, 180, 40);The QWidget.setGeometry() method takes four arguments: The first two arguments are the x and y coordinates of the button's top-left corner. The coordinates are relative to the parent widget. The last two arguments are the button's width and height. The result is a button that extends from position (10, 40) to position (190, 80).
window.show();When a parent widget is shown, it will call show for all its children (except those that were explicitly hidden using QWidget.hide()).
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