c++ - QToolButton 在按下 Alt 后显示菜单

Question

我有一个带有关联菜单的工具按钮。

m_mainMenuButton = new ToolButton("menu.png", tr("Open menu"));
m_mainMenuButton->setMenu(m_mainMenu);
m_mainMenuButton->setPopupMode(QToolButton::InstantPopup);

我希望在用户按下并释放 Alt 时显示此菜单。这样正常的 QMenuBar 在 Windows 上被激活(我想要这个工具按钮而不是 QMenuBar)。我试过这个:

m_mainMenuButton->setShortcut(QKeySequence(Qt::Key_Alt));

但是当按下并释放 Alt 时它不显示菜单。或者这样:

auto shortcut = new QShortcut(QKeySequence(Qt::Key_Alt), this);
connect(shortcut, &QShortcut::activated, m_mainMenuButton, &QToolButton::showMenu);

这也没有做任何事情。我试图覆盖按键和释放事件，但后来我发现它会干扰其他使用 Alt 键作为修饰符的快捷键，例如“Alt+Left”。

有什么办法吗？

更新一个显示 Alt 不能用作快捷方式的最小示例。

#include <QAction>
#include <QApplication>
#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
    menu->addAction("Action", [label]{ label->setText("Trigered!"); }, 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);

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

    return a.exec();
}

Answer 1

这是一个受 Qt 在 QMenuBar 中的实现启发的版本:

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();
}

Alt-Left 快捷键按预期工作，按钮菜单由 Alt-Pres-Release 切换。