如何排除一组事件不被 QT 的事件循环处理？

Question

I need to be able to exclude a set of events from being processed by the event loop; I am aware there are flags that can be passed onto processEvents method (eg QEventLoop::ExcludeUserInputEvents, which processes only events that are not user inputs, but leaves the user input events there for later processing), but is there a way to process only a specific subset (or, equivalently, exclude a specific subset) of events? I've been able to accomplish something similar using an event filter, but the events are discarded instead of simply not processing, which is not what I want. I was not able to find a way to do that, hence this question; would one have to rewrite QT's internals to do that or is there some functionality for that purpose? Thanks in advance!

Answer 1

At global level you can try to override QCoreApplication::notify() event handler. There you can create a set of event types which you ignore.

In the following example I override QApplication and ignore all mouse click related events. When clicking on the widget, there should be NO messages displayed. If you comment-out the notify() override, debug messages will be displayed.

#include <QApplication>
#include <QDebug>
#include <QWidget>

class Widget : public QWidget
{
public:
    void mousePressEvent(QMouseEvent *) override
    {
        qDebug() << "mouse button pressed";
    }
};

class Application : public QApplication
{
public:
    Application(int argc, char *argv[]) : QApplication(argc, argv)
    {
    }

    bool notify(QObject *object, QEvent *event) override
    {
        // e.g. sink for all mouse click events
        static QSet<int> ignoredEvents = { QEvent::MouseButtonPress, QEvent::MouseButtonRelease, QEvent::MouseButtonDblClick };
        if (ignoredEvents.contains(event->type()))
        {
            return true;
        }

        return QApplication::notify(object, event);
    }
};

int main(int argc, char *argv[])
{
    Application a(argc, argv);
    Widget w;
    w.show();
    return a.exec();
}