QMainWindow serves as the foundation for many desktop applications, providing a comprehensive window structure with various UI components. It includes a menu bar, multiple toolbars, dockable widgets, a status bar, and a central widget. This architecture makes it ideal for applications like text editors and image processing tools.

Key Components

Menu Bar

The menu bar presents a list of commands organized in menus. In Qt, consistency across menus, toolbar buttons, and keyboard shortcuts is achieved through QAction objects. Each menu consists of a collection of these actions, while the menu bar itself is the panel that hosts these menus at the top of the main window, below the title bar. A QMainWindow can have only one menu bar.

Status Bar

Typically positioned at the bottom of the main window, the status bar displays contextual information about the application's current state. It can accommoadte various Qt widgets to provide additional functionality. Like the menu bar, a QMainWindow supports only one status bar.

Toolbars

Toolbars contain frequently used commands represented as action buttons. They typically appear below the menu bar and above the status bar, but can be docked to any side of the main window (top, bottom, left, or right). Unlike menu bars and status bars, a QMainWindow can contain multiple toolbars.

Dock Widgets

Dock widgets act as containers for other UI components, enabling modular functionality. Examples include property editors and object inspectors in Qt Designer. These widgets can float freely over the main window or dock to any edge, similar to toolbars. A QMainWindow can host multiple dock widgets.

Central Widget

The central widget occupies the main area of the QMainWindow, surrounded by dock widgets. This is where the primary content of the application is displayed. Each QMainWindow can have only one central widget.

By default, QMainWindow provides a context menu to control the visibility of toolbars and dock widgets. This menu can be activated by right-clicking on toolbars or dock widgets, or programmatically through the QMainWindow::createPopupMenu() function. Developers can also override this function to implement custom context menus.

Project Framework Code

When creating a new Qt project, select "QMainWindow" as the base class. For our text editor example, we'll create a project named "TextEditor" with a main class called "TextEditApp". We'll start by creating the custom widget that will serve as our central widget.

contentwidget.h

#ifndef CONTENTWIDGET_H
#define CONTENTWIDGET_H

#include <QWidget>
#include <QLabel>
#include <QTextEdit>
#include <QImage>

class ContentWidget : public QWidget
{
    Q_OBJECT
public:
    explicit ContentWidget(QWidget *parent = nullptr);
    
    QImage documentImage;         // Document image
    QLabel *imageDisplay;          // Image display label
    QTextEdit *textEditor;        // Text editing area
signals:
    
public slots:
    
};

#endif // CONTENTWIDGET_H

contentwidget.cpp

#include "contentwidget.h"
#include <QHBoxLayout>

ContentWidget::ContentWidget(QWidget *parent) :
    QWidget(parent)
{
    imageDisplay = new QLabel;
    // Configure image scaling behavior
    imageDisplay->setScaledContents(true);

    // Set border styling
    imageDisplay->setStyleSheet("border: 1px solid black;");

    textEditor = new QTextEdit;

    // Set up the layout
    QHBoxLayout *primaryLayout = new QHBoxLayout(this);
    primaryLayout->addWidget(imageDisplay, 1);
    primaryLayout->addWidget(textEditor, 3);
}

texteditapp.h

#ifndef TEXTEDITAPP_H
#define TEXTEDITAPP_H

#include <QMainWindow>
#include <QImage>
#include <QLabel>
#include <QMenu>
#include <QMenuBar>
#include <QAction>