How to disable ALT + F4

[elizabeth.h1]

Hello

I want to prevent the user to prematurely closes my dialog box. So I disabled the close button in the system menu using setWindowFlags. But still ALT + F4 is working , and the user can close the dialog with this key combination. So , how to disable the ALT+ F4 to prevent closing, if this is possible at all ?

Thank you all

[kwisp]

see
QWidget::closeEvent ;
QCloseEvent ;
QEvent ;

[elizabeth.h1]

Yes I can ignore the event to prevent closing. But how can I ignore the event only if ALT +F4 was pressed ? i.e I don't want to ignore the event if the user closes the dialog with the X ( Close ) button. Or this is to much to ask ?

[Ginsengelf]

Hi, you can try to catch the keyPressEvent for ALT + F4, but I'm not sure if there is a keyPressEvent for this combination or if it just creates the closeEvent.

Ginsengelf

[elizabeth.h1]

I was looking to find the same , but can't find it.
I am sure there is must some way to say if ALT +F4 was pressed

[elizabeth.h1]

I try the following , but not working :

bool MyDlg::event(QEvent *event)
{
    QKeyEvent* myKeyEvent=(QKeyEvent*)event;
    if(myKeyEvent->matches(QKeySequence::Close))
        return true;
    return QDialog::event(event);
}

bool MyDlg::event(QEvent *event)
{
    QKeyEvent* myKeyEvent=(QKeyEvent*)event;
    if(myKeyEvent->matches(QKeySequence::Close))
        return true;
    return QDialog::event(event);
}

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[kwisp]

see my "crutch" example you can simplify it

#include <QApplication>
#include <QUrl>
#include <QVariant>
#include <QString>
#include <QtGlobal>
#include <QDebug>
#include <QWidget>
#include <QKeyEvent>
#include <QCloseEvent>
#include <QMouseEvent>
#include <QEvent>
 
class CloseHandler:public QObject {
	private:
		bool flag;
	protected:
		bool eventFilter(QObject* obj, QEvent* event)
		{
			if(obj->isWidgetType()) {
				switch(event->type()) {
					case QEvent::Close: {
						qDebug()<<__func__<<"Close";
						if(flag){
							event->ignore();
							return true;
						}
						//flag = false;
						break;
					}
					case QEvent::KeyPress: {
						if(((QKeyEvent*)event)->key() == Qt::Key_F4 || (((QKeyEvent*)event)->modifiers() == Qt::AltModifier)) {
							flag = true;
						}
						break;
					}
					case QEvent::MouseButtonPress://??
					case QEvent::MouseButtonRelease://??
					case QEvent::MouseMove://??
					case QEvent::Leave://!!
						flag = false;
					default: break;
				}
			}
			return QObject::eventFilter(obj,event);
		}
};
 
int main(int a ,char** b )
{
	QApplication app(a,b);
	QWidget w;
	CloseHandler h;
	w.installEventFilter(&h);
	w.show();
	return app.exec();
}

#include <QApplication>
#include <QUrl>
#include <QVariant>
#include <QString>
#include <QtGlobal>
#include <QDebug>
#include <QWidget>
#include <QKeyEvent>
#include <QCloseEvent>
#include <QMouseEvent>
#include <QEvent>

class CloseHandler:public QObject {
	private:
		bool flag;
	protected:
		bool eventFilter(QObject* obj, QEvent* event)
		{
			if(obj->isWidgetType()) {
				switch(event->type()) {
					case QEvent::Close: {
						qDebug()<<__func__<<"Close";
						if(flag){
							event->ignore();
							return true;
						}
						//flag = false;
						break;
					}
					case QEvent::KeyPress: {
						if(((QKeyEvent*)event)->key() == Qt::Key_F4 || (((QKeyEvent*)event)->modifiers() == Qt::AltModifier)) {
							flag = true;
						}
						break;
					}
					case QEvent::MouseButtonPress://??
					case QEvent::MouseButtonRelease://??
					case QEvent::MouseMove://??
					case QEvent::Leave://!!
						flag = false;
					default: break;
				}
			}
			return QObject::eventFilter(obj,event);
		}
};

int main(int a ,char** b )
{
	QApplication app(a,b);
	QWidget w;
	CloseHandler h;
	w.installEventFilter(&h);
	w.show();
	return app.exec();
}

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[wirasto]

How to disable escape key too ? I modified your code, but not work

case QEvent::KeyPress:
{
     if (((QKeyEvent*)event)->key() == Qt::Key_F4 || (((QKeyEvent*)event)->modifiers() == Qt::AltModifier))
     {
        flag = true;
     }
 
	//this is my code
     if (((QKeyEvent*)event)->key() == Qt::Key_Escape) {
         flag =true;
     }
 
     break;
}

case QEvent::KeyPress:
{
     if (((QKeyEvent*)event)->key() == Qt::Key_F4 || (((QKeyEvent*)event)->modifiers() == Qt::AltModifier))
     {
        flag = true;
     }

	//this is my code
     if (((QKeyEvent*)event)->key() == Qt::Key_Escape) {
         flag =true;
     }

     break;
}

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[wysota]

What is the point of disallowing the user to close the window using a keyboard shortcut and at the same time allow him to do it using the mouse? Both actions come from the user, why differentiate them?

[kwisp]

wirasto,
in what widget are you whant to ate escape?

[wirasto]

If me press Escape button then dialog will close. How to prevent it ? I must installEventFilter to every widget ?

[kwisp]

you mast read abut QDialog first of all.

after that i can suggest you to reimplement void QDialog::reject() [protected]
like this

...
void reject()
{
//nothing :)
}
...

...
void reject()
{
//nothing :)
}
...

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[elizabeth.h1]

"If me press Escape button then dialog will close. How to prevent it ? I must installEventFilter to every widget ?"

You can make new class , say MyQtDialog then reimplement keyPressEvent there like
this :

class MyQtDialog:public QDialog
{
  Q_OBJECT;
.....
 
void keyPressEvent(QKeyEvent* e)
{
   if(e->key() ==  Qt::Key_Escape)
       return;
 
}
}

class MyQtDialog:public QDialog
{
  Q_OBJECT;
.....

void keyPressEvent(QKeyEvent* e)
{
   if(e->key() ==  Qt::Key_Escape)
       return;
      
}
}

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Then use this class as base class for all dialog classes.

[wirasto]

I'm not create new class for QDialog, but I reimplement keyPressEvent in protected. And works now


kwisp,
Without installEventFilter and reimplement reject(), all close function can't work anymore This is amazing

[kwisp]

wirasto,
i do not understand you

[squidge]

I think he means keyPressEvent is virtual protected, and he has overrode its function. It's a standard thing to do in Qt land.

[kwisp]

i use eventFilter and installEventFilter becouse at begining this topick had very special question -- how to disable ALT+F4(Close window by X-button in top right coner and do not close by ALT+F4) i dont know realy why author whant this... he asked - i answer.

How to disable Key_Escape in QDialog? -- It is another question. Key_Escape is special key for QDialog. It is meaning -- QDialog::reject(). And i intend that if we whant not close dialog by reject we must write subclass(class MDialog: public QDialog) and reimplement virtual slot: void reject().
But this disable button "Cancel" and X-button.

If we whant to close dialog by "Cancel"-button and X-button, and do not close by Escape(i realy do not know what for) -- It is necessary to brain scatter.

[netmat]

hi,

is this piece of code worked for any of you guys?

//

.....
case QEvent::KeyPress: {

if(((QKeyEvent*)event)->key() == Qt::Key_F4 || (((QKeyEvent*)event)->modifiers() == Qt::AltModifier)) {

...........

//



I think "||" should be "&&".
Any way thats not important, what important is is this key sequence creating the close event that can be caught?
What i feel, its not taking the control to the code put with in such condition and the widget is being closed directly?

Could any one give a clear picture of catching the event created by Alt + F4?

Edit: Its creates a closeEvent(). but can we catch the key press like above?

[squidge]

Alt+F4 is a special key sequence (like Ctrl-Alt-Del), I don't think you can trap it without writing a driver. You can however (as stated above) trap the resulting close event.

[franz]

It is a good idea in general to keep standard key combinations working in your program. It helps making your program easier to use by decreasing the learning curve.