QToolButton在按下Alt键后显示菜单

以下是一个受Qt在 QMenuBar :

class AltButton : public QToolButton {
public:
    AltButton(QWidget *parent) : QToolButton(parent)
    {
        // To handle initial ALT-press in parent
        parent->installEventFilter(this);
        // If reparenting should be possible, override changeEvent
        // You can also make an app-wide event filter if the button should catch all alt presses
    }


protected:
    bool altPressed = false;
    bool eventFilter(QObject *watched, QEvent *event)
    {
        if (altPressed) {
            // Alt-press registered before, check alt-Release
            switch (event->type())
            {
            case QEvent::KeyPress:
            case QEvent::KeyRelease:
            {
                QKeyEvent *kev = static_cast<QKeyEvent*>(event);
                if (kev->key() == Qt::Key_Alt || kev->key() == Qt::Key_Meta) {
                    if (event->type() == QEvent::KeyPress)
                        break; // Alt-Press handled below by shortcut override
                    // Alt-Release. Toggle button
                    this->showMenu();
                }
            }
            // fallthrough
            case QEvent::MouseButtonPress:
            case QEvent::MouseButtonRelease:
            case QEvent::MouseMove:
            case QEvent::FocusIn:
            case QEvent::FocusOut:
            case QEvent::ActivationChange:
            case QEvent::Shortcut:
                // These events cancel a alt-trigger
                altPressed = false;
                // Stop listening for global alt-releas
                qApp->removeEventFilter(this);
                break;
            default:
                break;
            }
        } else if (isVisible()) {
            if (event->type() == QEvent::ShortcutOverride) {
                QKeyEvent *kev = static_cast<QKeyEvent*>(event);
                if ((kev->key() == Qt::Key_Alt || kev->key() == Qt::Key_Meta) && kev->modifiers() == Qt::AltModifier) {
                    // Alt-Press. Listen globally for alt-release
                    altPressed = true;
                    qApp->installEventFilter(this);
                }
            }
        }
        return false;
    }
};

int main(int argc, char**argv) {
    QApplication a(argc,argv);

        QMainWindow w;

        auto label = new QLabel();

        auto menu = new QMenu(&w);
        // intentionally added a shortcut which contains Alt as modifier to test it does not interfere with the menu
        menu->addAction("Action", [label]{ label->setText("Trigered!"); }, QKeySequence("Alt+Left"));

        auto btn = new AltButton(&w);
        btn->setMenu(menu);
        btn->setPopupMode(QToolButton::InstantPopup);

        // the following lines do not have any effect, the menu is not shown when Alt is pressed and released
        //auto shortcut = new QShortcut(QKeySequence(Qt::Key_Alt), &w);
        //QObject::connect(shortcut, &QShortcut::activated, btn, &QToolButton::showMenu);

        auto container = new QWidget();
        auto layout = new QVBoxLayout(container);
        layout->addWidget(btn);
        layout->addWidget(label);
        w.setCentralWidget(container);
        w.show();

        return a.exec();
}

尝试使用QObject::installEventFilter

例如

QtStackOverflow.h

#pragma once

#include <QtWidgets/QMainWindow>
#include <QToolButton>
#include "ui_QtStackOverflow.h"

class QtStackOverflow : public QMainWindow
{
    Q_OBJECT

public:
    QtStackOverflow(QWidget *parent = Q_NULLPTR);

private:
    Ui::QtStackOverflowClass ui;
};

class KeyPressEater : public QObject
{
   Q_OBJECT

public:
   KeyPressEater(QToolButton*btn) : keyOtherPush(false), keyAltPush(false) { _btn = btn; }

protected:
   bool eventFilter(QObject *obj, QEvent *event);

private:
   QToolButton * _btn;
   bool keyOtherPush;
   bool keyAltPush;
};

主.cpp

#include "QtStackOverflow.h"
#include <QtWidgets/QApplication>

#include <QObject>
#include <QEvent>
#include <QKeyEvent>
#include <QLabel>
#include <QMainWindow>
#include <QMenu>
#include <QShortcut>
#include <QToolButton>
#include <QVBoxLayout>

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

   QMainWindow w;

   auto label = new QLabel();

   auto menu = new QMenu(&w);
   // intentionally added a shortcut which contains Alt as modifier to test it does not interfere with the menu
   int number = 0;
   menu->addAction("Action", [label, &number] {
      label->setText(QString("%1 %2 ").arg("Trigered!").arg(number));
      number++;
   }, QKeySequence("Alt+Left"));

   auto btn = new QToolButton();
   btn->setMenu(menu);
   btn->setPopupMode(QToolButton::InstantPopup);

   // the following lines do not have any effect, the menu is not shown when Alt is pressed and released
   auto shortcut = new QShortcut(QKeySequence(Qt::Key_Alt), &w);
   QObject::connect(shortcut, &QShortcut::activated, btn, &QToolButton::showMenu);

   KeyPressEater *m_keyPressEater;
   m_keyPressEater = new KeyPressEater(btn);
   qApp->installEventFilter(m_keyPressEater);

   auto container = new QWidget();
   auto layout = new QVBoxLayout(container);
   layout->addWidget(btn);
   layout->addWidget(label);
   w.setCentralWidget(container);
   w.show();

   return a.exec();
}

bool KeyPressEater::eventFilter(QObject *obj, QEvent *event)
{
   if (event->type() == QEvent::KeyPress)
   {
      int key = static_cast<QKeyEvent *>(event)->key();

      if (key == Qt::Key_Alt)
      {
         keyAltPush = true;
      }
      else {
         keyOtherPush = true;
      }

      return QObject::eventFilter(obj, event);
   }
   else if (event->type() == QEvent::KeyRelease)
   {
      int key = static_cast<QKeyEvent *>(event)->key();

      if (key == Qt::Key_Alt) {
         if (keyAltPush == true && keyOtherPush == false) {
            _btn->showMenu();
         }
      }
      else {
         keyAltPush = false;
         keyOtherPush = false;
      }
      return true;
   }
   else {
      return QObject::eventFilter(obj, event);
   }
}

在这种情况下,你将得到所有的按键在任何时候。

然后需要检查QObject*senderObj=sender()