Highlighting Menu Items in Qt Widgets: QMenuBar::setActiveAction()

Purpose

• The highlighted action appears visually distinct from other menu bar items, often with a different background color or text style.
• In a QMenuBar (horizontal menu bar), this function sets the currently highlighted action.

Functionality

• If the QAction is not found within the QMenuBar's structure, no change occurs.
• If the provided QAction is part of the QMenuBar's menus (added using addMenu or other methods), it becomes the highlighted action.
• Takes a QAction* argument, which represents the action you want to make active.

Typical Usage

1. • Use the QAction class constructor to create an action object with the desired text, icon (optional), and behavior (connected to a slot using QObject::connect).

2. Add the QAction to a Menu or the QMenuBar (if desired)
   

   • Use QMenu::addAction to add the action to a specific QMenu (submenu).
   • Alternatively, use QMenuBar::addAction to add the action directly to the top level of the QMenuBar. This creates a menu item without a submenu.

3. Set the Active Action
   

   • Call QMenuBar::setActiveAction and pass the previously created QAction as the argument.

Example

#include <QApplication>
#include <QMainWindow>
#include <QMenuBar>
#include <QMenu>
#include <QAction>

int main(int argc, char *argv[]) {
    QApplication app(argc, argv);

    QMainWindow window;

    // Create a QMenuBar
    QMenuBar *menuBar = new QMenuBar(&window);
    window.setMenuBar(menuBar);

    // Create a QMenu
    QMenu *fileMenu = new QMenu("File");

    // Create a QAction
    QAction *openAction = new QAction("Open");

    // Connect the action to a slot (replace with your desired behavior)
    QObject::connect(openAction, &QAction::triggered, []() {
        // Handle open action
        qDebug() << "Open action triggered!";
    });

    // Add the action to the menu
    fileMenu->addAction(openAction);

    // Add the menu to the menu bar
    menuBar->addMenu(fileMenu);

    // Set the active action (assuming openAction is part of the menu structure)
    menuBar->setActiveAction(openAction);

    window.show();

    return app.exec();
}

Key Points

• Use this function strategically to provide visual feedback or guide the user's attention to specific menu items.
• To trigger the action's behavior, connect its triggered signal to a slot function.
• setActiveAction only affects the visual appearance (highlighting).

---

Example 1: Highlighting an Action in a Submenu

This example creates a QMenuBar with a "File" menu containing two actions: "Open" and "Save". It then sets the "Save" action as the active one:

#include <QApplication>
#include <QMainWindow>
#include <QMenuBar>
#include <QMenu>
#include <QAction>

int main(int argc, char *argv[]) {
    QApplication app(argc, argv);

    QMainWindow window;

    QMenuBar *menuBar = new QMenuBar(&window);
    window.setMenuBar(menuBar);

    QMenu *fileMenu = new QMenu("File");
    QAction *openAction = new QAction("Open");
    QAction *saveAction = new QAction("Save");

    fileMenu->addAction(openAction);
    fileMenu->addAction(saveAction);

    menuBar->addMenu(fileMenu);

    // Set "Save" as the active action
    menuBar->setActiveAction(saveAction);

    window.show();

    return app.exec();
}

Example 2: Dynamically Highlighting Based on User Interaction

This example creates a QMenuBar with two actions: "Cut" and "Copy". It connects the triggered signal of each action to a slot that sets the other action as active, simulating a toggle between the two:

#include <QApplication>
#include <QMainWindow>
#include <QMenuBar>
#include <QAction>

void setOtherActionActive(QAction* clickedAction, QAction* otherAction) {
    if (clickedAction != otherAction) {
        menuBar->setActiveAction(otherAction);
    }
}

int main(int argc, char *argv[]) {
    QApplication app(argc, argv);

    QMainWindow window;

    QMenuBar *menuBar = new QMenuBar(&window);
    window.setMenuBar(menuBar);

    QAction *cutAction = new QAction("Cut");
    QAction *copyAction = new QAction("Copy");

    QObject::connect(cutAction, &QAction::triggered, [=]() {
        setOtherActionActive(cutAction, copyAction);
    });

    QObject::connect(copyAction, &QAction::triggered, [=]() {
        setOtherActionActive(copyAction, cutAction);
    });

    menuBar->addAction(cutAction);
    menuBar->addAction(copyAction);

    window.show();

    return app.exec();
}

---

Using CSS Stylesheets

• You can define CSS rules to target specific menu items based on their properties (like text) and dynamically change their appearance (background color, text style) to mimic highlighting.
• Qt supports applying CSS stylesheets to widgets, including QMenuBar.

Example

/* Style for the active menu item */
QMenuBar::item:selected {
    background-color: lightblue;
    color: black; /* Adjust font color for better contrast */
}

Custom Signals and Slots

• Connect the signal to a slot in your QMenuBar class that modifies the appearance of the desired menu item (using CSS or manual changes).
• When a specific action needs to be highlighted, emit a signal from your application logic.
• Implement custom signals and slots to communicate between your application logic and the QMenuBar.

Reimplementing the Menu Bar

• You can then implement your own highlighting logic within this custom widget.
• If you have highly customized requirements or need more control over the menu bar's behavior, you can consider creating a custom widget that inherits from QWidget and replicates the functionality of a QMenuBar.

• Reimplement the menu bar for
  

  • Highly customized menu bar behavior
  • Need for complete control over the visual and interactive aspects

• Use custom signals and slots for
  

  • Complex highlighting logic based on application state
  • More decoupled architecture

• Use CSS stylesheets for
  

  • More granular control over appearance
  • Maintaining a clean separation between logic and presentation

• Use QMenuBar::setActiveAction() for
  

  • Simple highlighting needs
  • Easy implementation