How to get a if a KeySequence is pressed in main(); (While Application Launch)

ademmler

Hi there,

what is the way to get a KeySequence() within main() - aka while Applikation launch ?
When the MainWindow is active, this should have not influence any longer.

Use case: Some Application do a Maintenance task, if ALT is pressed while the start phase.

thx in Advance

Pl45m4

@ademmler

You could add a splash screen widget to your app which handles the key press events and triggers your maintenance action before your window shows up.
Or check within your window constructor if the ALT key is down and then do want you want to do.

Maybe even a custom QEventLoop which runs for like 1-2 seconds... in that time it checks if your keyevent was sent and then handles it before it exists again?!
(don't know if that works for you)

You could also make use of

https://doc.qt.io/qt-6/qguiapplication.html#keyboardModifiers

it's static so you can call it before your window shows up

ademmler

@Pl45m4

Hi, thx for all those nice hints. I ll check what is working for me and let you know.

ademmler

@Pl45m4

ok, I tried the solution using a Splash screen. - bracuase it exists anyway in my aplication.
Here is a stripped down code for testing. I get the splash screen, but not any Key-Event ...
Any ideas whats wrong?

main.cpp

#include "mainwindow.h"
#include "mysplashscreen.h"
#include <QApplication>
#include <QPixmap>
#include <QTimer>

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

    QPixmap pixmap(":logo");
    QSplashScreen splash(pixmap);
    splash.show();
    splash.raise();
    splash.activateWindow();

    qDebug() << "Splash screen is displayed.";

    // Delay splash screen
    QTimer::singleShot(3000, [&splash]() {
        splash.finish(nullptr);
    });

    // Proceed to the main window initialization here
    MainWindow mainWindow;
    mainWindow.show();

    return app.exec();
}

mysplashscreen.cpp

#include "mysplashscreen.h"

MySplashScreen::MySplashScreen(const QPixmap &pixmap) : QSplashScreen(pixmap) {
}

void MySplashScreen::keyPressEvent(QKeyEvent *event) {
    qDebug() << "Key Pressed:" << event->key(); /
    if (event->key() == Qt::Key_Escape) {
        qDebug() << "Escape key pressed during splash screen.";
        this->close();
    }
    QSplashScreen::keyPressEvent(event); // Ensure base class handling as well
}

mysplashscreen.h

#ifndef MY_SPLASH_SCREEN_H
#define MY_SPLASH_SCREEN_H

#include <QSplashScreen>
#include <QKeyEvent>
#include <QPixmap>
#include <QDebug>

class MySplashScreen : public QSplashScreen {
    Q_OBJECT 
public:
    explicit MySplashScreen(const QPixmap &pixmap);

protected:
    void keyPressEvent(QKeyEvent *event) override;
};

#endif // MY_SPLASH_SCREEN_H

Pl45m4

@ademmler said in How to get a if a KeySequence is pressed in main(); (While Application Launch):

// Delay splash screen
QTimer::singleShot(3000, [&splash]() {
    splash.finish(nullptr);
});

Try this instead:

MainWindow mainWindow;
splash.showMessage("Will close in 3s... Press [YourKey] for [YourAction");
splash.finish(&mainWindow);
QTimer::singleShot(3000, [&app, &mainWindow]() {
    app.processEvents();
    mainWindow.show();
});
return app.exec();

ademmler

@Pl45m4 HI -thanks for your response.

I have followed your advice - hopefully correct. But I do not see any "Message" and the key event does not get hit.
I am on MacOS - maybe it is OS related ...

#include "mainwindow.h"
#include "mysplashscreen.h"

#include <QApplication>
#include <QPixmap>
#include <QTimer>
#include <QEvent>

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

    // Create a pixmap to show on the splash screen
    QPixmap pixmap(":logo");
    QSplashScreen splash(pixmap);
    splash.show();
    splash.raise();
    splash.activateWindow();

    MainWindow mainWindow;
    splash.showMessage("Will close in 3s... Press [YourKey] for [YourAction");
    splash.finish(&mainWindow);
    QTimer::singleShot(3000, [&app, &mainWindow]() {
        app.processEvents();
        mainWindow.show();
    });

    return app.exec();
}

ademmler

Ok, I changed the Splash creation to this and now I can read the message:

QPixmap pixmap(100,100);
pixmap.fill(Qt::white);
QSplashScreen splash(pixmap);

But still the KeyEvent does not get hit. Didi I forgot to include something important.

jsulm

@ademmler Where do you use MySplashScreen?

ademmler

In main - because I want to get the KeyEvent before the MainWindow appears - see top to this thread.

Pl45m4

@ademmler

Urrgh... @jsulm is right...

Your splash variable has the type QSplashScreen...
You never create any instance of your custom MySplashScreen class, which handles the key event ;-)

I totally missed that... My code should work now

jsulm

@ademmler said in How to get a if a KeySequence is pressed in main(); (While Application Launch):

In main

no, you don't...

ademmler

Ok guys - you have been right - but still it does not work. I changed within main() to:

// Create a pixmap to show on the splash screen
QPixmap pixmap(500,100);
pixmap.fill(Qt::white);
MySplashScreen splash(pixmap);
splash.show();
splash.raise();
... and so on

jsulm

@ademmler Maybe your splash screen does not have focus? Try to klick on it and then press a key.

Pl45m4

@ademmler

This works for me:

    QPixmap pixmap(500,100);
    pixmap.fill(Qt::white);
    MySplashScreen splash(pixmap);
    splash.show();
    QTimer::singleShot(3000, &app, [&]() {
        // even with finish() outside the lamda,
        // but then you have to be fast with pressing the key
        splash.finish(&w);
        app.processEvents(); // needed?!
        w.show();
    });

@jsulm clicking will make the Splash screen disappear.
The above code works for me on Windows without doing anything... Splash shows up, I spam ESC-key, I get dozens of Key pressed messages from my qDebug in SplashScreen's keyEvent handler.

Edit:

Weird that I don't even need the processEvents call... commented that line, still works.

ademmler

@jsulm Hi, when I do so the Splash window vanishes imdiatly. I tried also to use splash.setFocus ();

ademmler

@Pl45m4 Hi - thx again. I copied your code 1:1 and added "MainWindow w;" above.
when I am not mistaken I should get - as you do "Any key printed" as Debug message, because I have
a genial log message for any Key also.

But still - being on Mac OS - I do not get a Debug() message and also, when I run in Debugger mode, the routine gets never hit.

I ll try on windows - for cross test now ...

jsulm

@ademmler Try to play with some flags like: Qt::WindowTransparentForInput and Qt::WindowDoesNotAcceptFocus. Maybe on Mac splash screen does not accept key events by default.

ademmler

Hi, to both of you - I can approve on Windows 11 it is working as expected.
Hence the question is whats needed for MacOS to get it work or is it a Bug ...

@jsulm Yep I will test the flags and let you know.

Pl45m4

@ademmler said in How to get a if a KeySequence is pressed in main(); (While Application Launch):

Hence the question is whats needed for MacOS to get it work or is it a Bug ...

Either bug or just how it works on Mac...

See:
(also includes a workaround... )

https://stackoverflow.com/questions/23728058/get-keypresses-in-qsplashscreen-on-osx

maybe worth a try if you are fine with creating an empty widget/window before the splashscreen is created

ademmler

@Pl45m4 Hi, thx for pointing me to the stack overflow thread. I have tried two things:

I just added this splash.grabKeyboard();:
In this case the key event gets hit, when MainWindow is active.
The solution from stack overflow is adding a "hidden" window before the Splashscreen is called.
But also in this case the key event gets hit, when MainWindow is active. This would have a negative effect on the Main Application for sure.

Maybe the simplest way is to create my Own "Dialog" or Framless Widget as a Splashscreen replacement ...
The Event filter should be no longer active, when the dialog has been closed - right?