Customizing Tab Behavior with QTabBar::mouseDoubleClickEvent()

Purpose

• This function is triggered whenever the user double-clicks on a tab within the QTabBar widget.

How it works

• This function receives a QMouseEvent object as input, containing details about the double-click event, such as the position of the click and any modifier keys that were pressed (e.g., Ctrl, Shift).
• When a double-click occurs on a tab, Qt detects it and sends the mouseDoubleClickEvent() signal to the QTabBar object.
• Qt internally tracks mouse events like clicks and double-clicks.

What you can do in the function

• For example, you might:
  • Switch to the tab that was double-clicked (assuming you have a mechanism to identify the clicked tab).
  • Trigger some other action specific to your application based on the double-click.
• Inside the mouseDoubleClickEvent() function, you can write custom logic to handle the double-click event.

Important points to remember

• You can access information about the double-click event from the provided QMouseEvent object.
• Qt doesn't provide default behavior for mouseDoubleClickEvent(). It's entirely up to you to implement the desired functionality within this function.

---

#include <QApplication>
#include <QtWidgets>

class MyWindow : public QWidget {
  Q_OBJECT

public:
  MyWindow(QWidget *parent = nullptr) : QWidget(parent) {
    // Create a layout and add a QTabBar widget
    QVBoxLayout *layout = new QVBoxLayout(this);
    tabBar = new QTabBar(this);
    tabBar->addTab("Tab 1");
    tabBar->addTab("Tab 2");
    tabBar->addTab("Tab 3");
    layout->addWidget(tabBar);

    // Connect the mouseDoubleClickEvent signal to a custom slot
    connect(tabBar, SIGNAL(mouseDoubleClickEvent(QMouseEvent*)), this, SLOT(onTabDoubleClicked(QMouseEvent*)));
  }

private slots:
  void onTabDoubleClicked(QMouseEvent* event) {
    // Get the index of the double-clicked tab
    int tabIndex = tabBar->tabAt(event->pos());

    // Check if a valid tab was clicked
    if (tabIndex != -1) {
      tabBar->setCurrentIndex(tabIndex);  // Switch to the double-clicked tab
    }
  }

private:
  QTabBar *tabBar;
};

int main(int argc, char *argv[]) {
  QApplication app(argc, argv);
  MyWindow window;
  window.show();
  return app.exec();
}

1. We create a MyWindow class that inherits from QWidget.
2. Inside the constructor, we create a QTabBar widget and add three tabs to it.
3. We connect the mouseDoubleClickEvent signal emitted by tabBar to a custom slot named onTabDoubleClicked.
4. The onTabDoubleClicked slot receives a QMouseEvent object as input.
5. We use tabBar->tabAt(event->pos()) to get the index of the tab that was clicked based on the mouse position in the event.
6. If a valid tab was clicked (index != -1), we use tabBar->setCurrentIndex(tabIndex) to switch the currently selected tab to the double-clicked one.

---

1. Using QAbstractButton::clicked() signal
   

• Inside the connected slot, check the number of clicks using QAbstractButton::clickCount(). If it's 2, you can perform the double-click action.
• You can connect to this signal instead of mouseDoubleClickEvent().
• QTabBar inherits from QAbstractButton, so it inherits the clicked() signal.

1. Custom Event Handling
   

• Emit your custom signal when a double-click is detected.
• For example, connect to QTabBar::mousePressEvent() and check for double clicks based on stored click information.
• You can create a custom event signal within your class and emit it from within another event handler related to mouse clicks on the tab bar.

1. Using a Timer
   

• Remember to stop the timer on any other event (e.g., mouse release) to avoid unintended triggers.
• If another click occurs within a certain time window before the timer expires, consider it a double-click and perform your desired action.
• Start a timer on click.
• Connect to QTabBar::mousePressEvent().
• This approach is less efficient but might be suitable for specific scenarios.

Choosing the Right Approach

The best alternative depends on your specific needs:

• For more complex scenarios or custom logic, creating a custom event or using a timer with careful handling could be more suitable.
• If you only care about basic double-click functionality, using clicked() with a click count check might be sufficient.

• Consider using higher-level Qt components like QTabWidget which already handle tab selection and might offer built-in double-click functionality.
• Qt provides a QApplication::doubleClickInterval property to control the system-wide double-click detection time. This might affect your implementation's behavior.