Free memory

[TomASS]

Hi,

I'm creating a form by:

FormPusty::FormPusty(QWidget *parent) : QMainWindow(parent)
{
 
    base = new QWidget();
    QGridLayout *layout = new QGridLayout(base);
    QTabWidget *TwNew = new QTabWidget();
    QWidget *page1 = new QWidget();
    TwNew->addTab(page1,QIcon::QIcon(":/new/prefix1/doc_stand.png"),"pierwsze");
 
    layout->addWidget(TwNew,0,0,1,1);
    base->show();
    this->setCentralWidget(base);
    this->move(((QApplication::desktop()->width()-this->width())/2),((QApplication::desktop()->height()-this->height())/2));
 
}

FormPusty::FormPusty(QWidget *parent) : QMainWindow(parent)
{

    base = new QWidget();
    QGridLayout *layout = new QGridLayout(base);
    QTabWidget *TwNew = new QTabWidget();
    QWidget *page1 = new QWidget();
    TwNew->addTab(page1,QIcon::QIcon(":/new/prefix1/doc_stand.png"),"pierwsze");
    
    layout->addWidget(TwNew,0,0,1,1);
    base->show();
    this->setCentralWidget(base);
    this->move(((QApplication::desktop()->width()-this->width())/2),((QApplication::desktop()->height()-this->height())/2));

}

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and in application:

OFormPusty = new FormPusty();
OFormPusty->show();

OFormPusty = new FormPusty();
OFormPusty->show();

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and I've discovered there is no free memory in my app :/ How to add a free memory, I've a several forms whith alocated almost 10Mb :/ when I'm closing a form memeory is still use :/
ofcourse I've :

FormPusty::~FormPusty(){
 qDebug()<<"ttt";
 delete base ;
}

FormPusty::~FormPusty(){
 qDebug()<<"ttt";
 delete base ;
}

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but is noting happend :/

[Archimedes]

This is working as intended. If you show() a dialog after you close it its destructor don't get called and it's there to be used again.
On the contrary if you exec() a dialog when you close the instant gets destructed. The difference between those 2 function is when you
show() the dialog is modeless and on exec() it's modal. See more on the documentation about this.

[TomASS]

Thanks - you have said that replace show() to exec() solve my problem, unfortunately there's no member function llike exec() in QMainWindow :/

[Lykurg]

well to possibilities:
Have you "OFormPusty = new FormPusty();" in a function which is called multiple times? then you have to use "delete OFormPusty;" or use QObject::deleteLater().
Or how do you measure the occupied space? Sometimes the memory is freed but still assigned to the app if it need it again. So there must not be a real memory leak.

[TomASS]

Yes, a I've exactly:

void MainWindow::slotFormPusty(){
OFormPusty = new FormPusty ();
connect(OFormPusty , SIGNAL(singalDone()), this, SLOT(slotDone()));      
 
      OFormPusty ->show();
}

void MainWindow::slotFormPusty(){
OFormPusty = new FormPusty ();
connect(OFormPusty , SIGNAL(singalDone()), this, SLOT(slotDone()));      
     
      OFormPusty ->show();
}

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OFormPusty is a member of MainWindow.

you said than I should write delete OFormPusty; a in slotDone() ?
I mesure the occupied space by Windows task manager

[Lykurg]

if there should be only one window use

void MainWindow::slotFormPusty(){
if(OFormPusty)
  OFormPusty->deleteLater();
OFormPusty = new FormPusty ();
connect(OFormPusty , SIGNAL(singalDone()), this, SLOT(slotDone()));      
 
      OFormPusty ->show();
}

void MainWindow::slotFormPusty(){
if(OFormPusty)
  OFormPusty->deleteLater();
OFormPusty = new FormPusty ();
connect(OFormPusty , SIGNAL(singalDone()), this, SLOT(slotDone()));      
     
      OFormPusty ->show();
}

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if you have more instances of that form set the widget attribute Qt::WA_DeleteOnClose to ensure that the memory gets freed after closing the window.


EDIT: If there is only one instance a time, don't create a new one, just reuse the old one:

void MainWindow::slotFormPusty(){
  if(!OFormPusty)
    OFormPusty = new FormPusty ();
 
  connect(OFormPusty , SIGNAL(singalDone()), this, SLOT(slotDone()));         
  OFormPusty ->show();
}

void MainWindow::slotFormPusty(){
  if(!OFormPusty)
    OFormPusty = new FormPusty ();

  connect(OFormPusty , SIGNAL(singalDone()), this, SLOT(slotDone()));         
  OFormPusty ->show();
}

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[TomASS]

Thank's Lykurg! You've a right.

[TomASS]

Unfortunately, I've somthing strange:

I put:

if(OFormPusty){
        OFormPusty->deleteLater();
        delete OFormPusty;
    }
OFormPusty= new OFormPusty();

if(OFormPusty){
        OFormPusty->deleteLater();
        delete OFormPusty;
    }
OFormPusty= new OFormPusty();

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Sometimes (50% cases) when I've compiled my app this code throw me an error (debug shows me QWaitCondition: Destroyed while threads are still waiting ) - when I compiled again, it should be good (but not sure) :/

[aamer4yu]

OFormPusty->deleteLater(); schedules the deletion in next event loop.
So you shouldnt use it. This should work fine -

if(OFormPusty){
        delete OFormPusty;
        OFormPusty = 0;    // To prevent improper use if any.
    }
OFormPusty= new OFormPusty();

if(OFormPusty){
        delete OFormPusty;
        OFormPusty = 0;    // To prevent improper use if any.
    }
OFormPusty= new OFormPusty();

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But why so you want to delete and create again ? As Lykurg said, you can do with single object

[TomASS]

Thank's

I'ld like to create a new window (new OFormPusty), when user push the button (it does not make sense create a form when application is starting). When user close a form and push the button again, I'ld like to show form with new contents so, delete and create a form is fine for me...i think so.

[Lykurg]

When user close a form and push the button again, I'ld like to show form with new contents so, delete and create a form is fine for me...i think so.

Well it works but it is not fine! use this and try to fully understand what the code is doing:

void MainWindow::slotFormPusty(){
  // next lines checks if the form exists, because on the initialisation of the class the form is not created!
  // so it is only created if the user request it.
  if(!OFormPusty)
  {
    OFormPusty = new FormPusty ();
    connect(OFormPusty , SIGNAL(singalDone()), this, SLOT(slotDone()));
    // do initial setup here
  }
  QFormPusty->setToDefault(); // this is a custom slot that should clear al temporary data. So that the form is "new"
  OFormPusty ->show();
}

void MainWindow::slotFormPusty(){
  // next lines checks if the form exists, because on the initialisation of the class the form is not created!
  // so it is only created if the user request it.
  if(!OFormPusty)
  {
    OFormPusty = new FormPusty ();
    connect(OFormPusty , SIGNAL(singalDone()), this, SLOT(slotDone()));
    // do initial setup here
  }
  QFormPusty->setToDefault(); // this is a custom slot that should clear al temporary data. So that the form is "new"
  OFormPusty ->show();
}

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This is - as far as I know - the best solution for you.

But as said your way works also.

Lykurg


P.s.: the difference is that the above version will require space permanently and your approach only need the space temporary but require always a new creation of the form which costs cpu power.