Button Press vs Key Press

admkrk

I am working on a synthesizer application that can use a button press or a key press to emit a signal. There was no problem with just the buttons, but when I added the key events, that does not work unless a button is pressed first.

void KeyPad::on_key_A_pressed()
{
    emit noteOn(A);
}

void KeyPad::keyPressEvent(QKeyEvent *event)
{
    switch(event->key())
    {
    case Qt::Key_Z:
        ui->key_A->setDown(true);
        emit noteOn(A);
        break;
	// ...
    }
}

If I change the wave shape, the keyboard goes back to not working until I press a button again. Can someone explain to me why a button needs to be pressed before the key event is triggered?

JonB

@admkrk
I'm not sure I understand, but if you call QAbstractButton::setDown(true) explicitly, aren't you responsible for also calling QAbstractButton::setDown(false)? Else Qt will see that button as down but not up, and be in a messed state?

admkrk

Yes, I also handle the release.

void KeyPad::keyReleaseEvent(QKeyEvent *event)
{
    switch(event->key())
    {
    case Qt::Key_Z:
        ui->key_A->setDown(false);
        break;
	// ...
    }

    emit noteOff();
}

That is just so you can see something happening in the GUI. I had the same behavior before adding that bit, so I do not see it as being related.

I tried calling on_key_A_pressed() instead of emitting the signal directly, but that made no difference. This leads me to believe that the press event is not registering until a button is pressed first. Further, any change to the GUI, other than pressing a button, resets it to not registering until a button is pressed again. I do not understand why this is happening.

Christian Ehrlicher

Can you please explain what you're doing and what exactly is wrong? I read it twice but still don't understand the problem.

admkrk

Sorry for the bad explanation, I will try to do better. I think the confusion is because the buttons are representing keys on a keyboard(the GUI element) while I am referring to key presses on the computer keyboard. Maybe an image will help?

When I press one of the assigned keys (on the computer keyboard), nothing happens until I first press one of the buttons. Then it all works fine. If I interact with anything else in the GUI, it no longer responds to the keyboard, until I press a button again.

OK, I narrowed it down a bit. It seems the problem is that the key presses are only registered when my KeyPad has focus. I never considered that would make a difference. The sliders and dials all respond to the mouse regardless of what has focus. Is there a way to have the key presses work the same way?

I hope that is clearer.

hskoglund

The key presses go to the window that has focus, so if your KeyPad is only a small window (a small part of your app) then it's better to check for the key presses in your main app window.

SGaist

Hi,

Aren't you re-implementing QShortcut ?

admkrk

@SGaist said in Button Press vs Key Press:

Hi,

Aren't you re-implementing QShortcut ?

I thought about that at first, but that seems to only trigger clicked() and holding the key just repeatedly triggers it.

@hskoglund said in Button Press vs Key Press:

The key presses go to the window that has focus, so if your KeyPad is only a small window (a small part of your app) then it's better to check for the key presses in your main app window.

It is actually a custom widget. I am already getting a bit of latency and that will probably make it worse, but I guess that might be my best option. I will give that a try and see how it works.

admkrk

Handling the key presses in the main window did solve my problem, thanks.

I am unsure about how it effected the latency, I can work on that later.

Thanks again!