at eventFilter(QObject *object, QEvent *event), can't get keyPress events when the MainWindow is hidden.

Miguel de Sousa

I Have created a MainWindow class that inherits from QMainWindow. Inside this window, I want to get keyboard events while this window is visibile or invisible. In my program, this window could be visible or invisible, depending on the context.

MainWindow.cpp:

MainWindow::MainWindow()  {
    //..
    QCoreApplication::instance()->installEventFilter(this);
   //..
}

    bool MainWindow::eventFilter(QObject *object, QEvent *event) {
        qDebug() << "print my event: " << event;
        if (event->type() == QEvent:KeyPress) {
                doSomething();
    }
        return false;
    }

This works perfectly fine while the MainWindow is visible. I can get all sort of QKeyEvents, printing them like this:

print my event: QKeyEvent(KeyPress, key=0x34, text="4")
print my event: QKeyEvent(keyRelease, key=0x34, text="4)

However, when I hide the MainWindow with this->hide(), problems start to arise.
When the window is hidden, I can't get KeyPress events, and the events are printed like this:

print my event: QEvent(SockAct, oxbe971a9c, type = 50)

That is, I expected to get KeyPress events, but all I can get are these Socket Activation events.

Does anyone know how can I get KeyPress events when my MainWindow is hidden?
I'm using Qt 4.8.7.

SGaist

Hi and welcome to devnet,

AFAIK you can't.

What are you trying to achieve exactly ?

Miguel de Sousa

HI, SGaist!

What I want to achieve is an application that, by pressing a key combination from the keyboard, I could make a window invisible. When pressing again this combination, I could make it visible again.

Notice that this window is frameless. In my project I only have a main.cpp, a mainwindow.cpp and another class with some inner logic for measuring the system memory usage.

The UI logic is all inside the main.cpp and on the mainwindow.cpp.

my main.cpp:

#include "mainwindow.h"
#include <QApplication>
#include <QtGui>
#include <stdlib.h>
#include <QWSServer>
#include <QDebug>

int main(int argc2, char *argv2[])
{
   //..
    QWSServer::setBackground(QBrush(Qt::transparent));

    QApplication a(argc, argv);
    MainWindow *window = new MainWindow();

    window->setWindowFlags(Qt::FramelessWindowHint);
    window->setFixedSize(QDesktopWidget().width()*0.83, QDesktopWidget().height()*0.33);
    window->setGeometry(QStyle::alignedRect(Qt::LeftToRight, Qt::AlignCenter,
                                           window->size(), a.desktop()->availableGeometry()));

        window->show();
    return a.exec();
}

my mainwindow.cpp:

#include<QtGui>
#include "mainwindow.h"
#include "ui_mainwindow.h"
#include "memoryhandler.h"
#include <QDebug>
#include <QKeyEvent>

MainWindow::MainWindow()  {
    memoryHandler = new MemoryHandler();
    setTimer();
    QCoreApplication::instance()->installEventFilter(this);
    initializeKeyboardState();
    initializeLayout();
    initializeLabels();
    updateLabels();
    addLabelsToLayout();
    boxLayout->setSizeConstraint(QLayout::SetMinimumSize);
    isApplicationVisible = true;
}

void MainWindow::setTimer()
{
    timer = new QTimer(this);
    QObject::connect(timer, SIGNAL(timeout()), this, SLOT(updateLabels()));
    timer->start(1000);
}

void MainWindow::initializeKeyboardState()
{
    keyboardState.isShortcutKeyPressed = false;
    keyboardState.is4KeyPressed = false;
    keyboardState.is2KeyPressed = false;
}

void MainWindow::initializeLayout()
{
 //...
}

void MainWindow::updateLabels() {
//...
}

void MainWindow::initializeLabels()
{
//...
}

void MainWindow::addLabelsToLayout()
{
//...
}

QString MainWindow::format(QString prefix, float value) {
    QString valueAsString = QString::number(value);
    return prefix + " = " + valueAsString + "Mb";
}

QString MainWindow::formatPercentage(QString prefix, float value) {
    QString valueAsString = QString::number(value);
    return prefix + " = " + valueAsString + "%";
}


    bool MainWindow::getApplicationVisibility() {
        return isApplicationVisible;
    }

    bool MainWindow::eventFilter(QObject *object, QEvent *event) {
        qDebug() << "print the event: " << event;
        if (event->type() == QEvent::KeyPress) {
                qDebug() << "gotcha";
    }
        return false;
    }

    void MainWindow::keyPressEvent(QKeyEvent *event) {
        qDebug() << "pressed, calling keyPressEvent";
        switch (event->key()) {
        case Qt::Key_Shift:
            keyboardState.isShortcutKeyPressed = true;
            break;
        case Qt::Key_4:
            keyboardState.is4KeyPressed = true;
            break;
        case Qt::Key_2:
            keyboardState.is2KeyPressed = true;
            break;
        }
        decideWindowVisibility();
    }

    void MainWindow::decideWindowVisibility()
    {
        if (isKeyboardStateTrue()) {
            if (isApplicationVisible) { this->hide(); }
            else { this->show(); }
            isApplicationVisible = !isApplicationVisible;
        }
    }

    bool MainWindow::isKeyboardStateTrue() {
        if (keyboardState.isShortcutKeyPressed &&
                keyboardState.is4KeyPressed &&
                keyboardState.is2KeyPressed)
            return true;
        return false;
    }

        void MainWindow::keyReleaseEvent(QKeyEvent *event) {
            qDebug() << "soltou, chamou keyReleaseEvent";
            switch (event->key()) {
            case Qt::Key_Escape:
                keyboardState.isShortcutKeyPressed = false;
                break;
            case Qt::Key_4:
                keyboardState.is4KeyPressed = false;
                break;
            case Qt::Key_2:
                keyboardState.is2KeyPressed = false;
                break;
            }
    }

MainWindow::~MainWindow()
{
    delete ui;
    delete memoryHandler;
}

SGaist

Are you running that application on an embedded device ?

Miguel de Sousa

Yes, I am :')

SGaist

Then is your application the only one running ?

What do you do with it when your MainWindow gets hidden ?

Miguel de Sousa

Actually, there's a application running behind.

In some moment, I intend to make the application behind start the foreground window, so the foreground window could display the memory usage for the user.

I expected that both applications could catch events, but I'm having this problem with KeyPress events on this memory window thing, coming like Socket Activation events.

SGaist

Is this other application sharing the QWS server ?