问题描述

我有一个可用的应用程序.我向带有一些菜单的主窗口添加了一个 menuBar().然后，我将其隐藏以释放屏幕空间.我写了下面的代码，这样当用户按下 ALT 键时，菜单栏如果隐藏就会出现，如果显示则隐藏.

void MainWindow::keyPressEvent( QKeyEvent *k ) {if(k->modifiers() & Qt::AltModifier) {menuBar()->setHidden(!menuBar()->isHidden());if(menuBar()->hasFocus()) {QMessageBox::information(this, "Info", "Focus !");}}}

如你所见，我还添加了一个 QMessageBox 来查看 menuBar 何时获得焦点.而这个框只出现一半的时间.它是这样的:

1. 应用启动，菜单栏隐藏
2. 我按下 ALT，显示菜单栏，没有消息框，没有焦点
3. 我按下 ALT，隐藏菜单栏
4. 我按下 ALT，显示菜单栏，消息框，焦点
5. 我按下 ALT，隐藏菜单栏
6. 我按下 ALT，显示菜单栏，没有消息框，没有焦点
7. 我按下 ALT，隐藏菜单栏
8. 我按下 ALT，显示菜单栏，消息框，焦点
9. 等

如何确保menuBar在显示时始终有焦点?

我想做同样的事情.我的解决方案，完整示例，作为要点:

https://gist.github.com/xim/ee56564f425151ea2fa70f7830d

针对 Qt 5.9.4 进行测试.

因为它包含很多其他垃圾，一个最小的例子:

class AutoHidingMenuBar : public QMenuBar {Q_OBJECT上市:AutoHidingMenuBar() : QMenuBar() {设置最大高度(0)；连接(qApp, &QApplication::focusChanged, this, &AutoHidingMenuBar::focusChanged);}私人插槽:void focusChanged(QWidget *from, QWidget *to) {bool inFocus = hasFocus() ||isAncestorOf(focus) ||hasFocusedChild();if (inFocus &&maximumHeight() == 0) {自动动作 = activeAction();设置最大高度(100)；如果(动作){//XXX 这是一个小技巧.我们可以做//QCoreApplication::processEvents();//setActiveAction(action);//效果几乎相同，但随后我们*打开*了单次按下 alt 时的第一个菜单...auto evt = new QMouseEvent(QEvent::MouseMove, actionGeometry(action).center(), Qt::NoButton, Qt::NoButton, Qt::NoModifier);QCoreApplication::postEvent(this, evt);}} else if (!inFocus &&maximumHeight() != 0)) {设置最大高度(0)；}}私人的:bool hasFocusedChild() {QObjectList 队列{children()};而 (!queue.empty()) {auto child = queue.takeFirst();自动小部件 = dynamic_cast<QWidget *>(child);if (widget && widget->hasFocus())返回真；queue.append(child->children());}返回假；}};

I have a working application. I added a menuBar() to the main window with some menus. Then, I hid it to free screen space. I wrote the code below so that when user presses ALT key, the menu bar appears if it's hidden, and it hides if it's displayed.

void MainWindow::keyPressEvent( QKeyEvent *k ) {
    if(k->modifiers() & Qt::AltModifier) {
        menuBar()->setHidden(!menuBar()->isHidden());
        if(menuBar()->hasFocus()) {
            QMessageBox::information(this, "Info", "Focus !");
        }
    }
}

As you can see, I also added a QMessageBox to see when the menuBar has the focus. And this box appears only half of the time. It goes like this :

1. Application launched, menubar hidden
2. I press ALT, menubar displayed, no message box, no focus
3. I press ALT, menubar hidden
4. I press ALT, menubar displayed, message box, focus
5. I press ALT, menubar hidden
6. I press ALT, menubar displayed, no message box, no focus
7. I press ALT, menubar hidden
8. I press ALT, menubar displayed, message box, focus
9. etc.

How to make sure when the menuBar is displayed, it always has focus ?

I wanted to do the same thing. My solution, complete example, as a gist:

https://gist.github.com/xim/ee56564f425151ea2fa70f730d644873

Tested against Qt 5.9.4.

As it contains a lot of other junk, a minimal example:

class AutoHidingMenuBar : public QMenuBar {
    Q_OBJECT

public:
    AutoHidingMenuBar() : QMenuBar() {
        setMaximumHeight(0);
        connect(qApp, &QApplication::focusChanged, this, &AutoHidingMenuBar::focusChanged);
    }

private slots:
    void focusChanged(QWidget *from, QWidget *to) {
        bool inFocus = hasFocus() || isAncestorOf(focus) || hasFocusedChild();
        if (inFocus && maximumHeight() == 0) {
            auto action = activeAction();
            setMaximumHeight(100);
            if (action) {
                // XXX This is a bit of a hack. We could do
                //   QCoreApplication::processEvents();
                //   setActiveAction(action);
                // with almost the same effect, but then we *open* the first menu on single alt press...
                auto evt = new QMouseEvent(QEvent::MouseMove, actionGeometry(action).center(), Qt::NoButton, Qt::NoButton, Qt::NoModifier);
                QCoreApplication::postEvent(this, evt);
            }
        } else if (!inFocus && maximumHeight() != 0)) {
            setMaximumHeight(0);
        }
    }

private:
    bool hasFocusedChild() {
        QObjectList queue{children()};
        while (!queue.empty()) {
            auto child = queue.takeFirst();
            auto widget = dynamic_cast<QWidget *>(child);
            if (widget && widget->hasFocus())
                return true;

            queue.append(child->children());
        }
        return false;
    }
};

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