Constructor arguments of QKeyEvent ?

[Andy314]

Hello,
I must implement a simple virtual keyboard. It is not all clear for me how to do it. Buttons/Layout etc. is simple but how to send the keys.
Here some code examples:

QWidget * w = QApplication::focusWidget();
   if(!w)
       return;
   QKeyEvent e(QEvent::KeyPress, Qt::Key_X,Qt::NoModifier, "ab");
   QApplication::sendEvent(w, &e);
   QKeyEvent e2(QEvent::KeyRelease, Qt::Key_A,Qt::NoModifier, "a");
   QApplication::sendEvent(w, &e2);

Unclear is the constructor of QKeyEvent. Why argument 2 AND argument 4.
Argument 2 should describe the key. For what is argument 4. I found that this string (multiple chars) will be send to the input widget and I must set here a string which is independent of argument 2. For what is argument 2 then ?
Second question is: Must I send a keyrelease for proper working of the virtual keyboard.
Any other tips for a developing a virtual keyboard are welcome, too.

[mrjj]

@Andy314

Hi
I would seek inspiration in existing implementations
like
https://www.linux-apps.com/p/1132203/

[SGaist]

Hi,

The QKeyEvent constructor documentation explains all the parameters.

[Andy314]

Hello @mrjj ,
as a inspiration it is good.
They use an other concept, in the close sense it is not really a virtual keyboard. It works only with a QLineEdit (and its subclasses) and sends keystrokes never but rather manipulates the QLineEdit::text directly.

In general I dont understand, why I must send a keystroke to a special widget with the following code (I in my code I look for the focused.)
QApplication::sendEvent(wiget, &event);
This works only for Qt-Apps. Why can I not send a key to the operating system and the system processes it relating to its rules ?

[mrjj]

@Andy314
Oh, sorry I thought it would be more clever made.
To send events to the OS, you need to use native API.

Qt has support for handling the virtual keyboard
http://doc.qt.io/qt-4.8/qt-tools-inputpanel-example.html
notice the QEvent::RequestSoftwareInputPanel
I have not tested these on Desktop but Docs seems not to limit use.

If you want to make a native virtual keyboard that work with ANY app, you need to dive into the native app for that.