Qt::WA_DeleteOnClose

Question

I am learning Qt and trying some examples in the book "Foundations of Qt Development". In the book, there is a section teaching Single Document Interface with an example creating a simple app like a notepad.

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    setAttribute(Qt::WA_DeleteOnClose);
    setWindowTitle(QString("%1[*] - %2").arg("unnamed").arg("SDI"));

    connect(ui->docWidget->document(), SIGNAL(modificationChanged(bool)), this, SLOT(setWindowModified(bool)));

    createActions();
    createMenu();
    createToolbars();

    statusBar()->showMessage("Done");    
}

The book said that "Setting the windows attribute to Qt::WA_DeleteOnClose so that Qt takes care of deleting the window from memory as soon as it is closed.

How it works?

Because if i use setAttribute(Qt::WA_DeleteOnClose);, when I end the program, there is a Debug Assertion Failed warning:_BLOCK_TYPEIS_VALID(pHead->nBlockUse). There is no problem if the setAttribute is removed.

Answer 1

Qt takes care of the deletion by itself if you set all the parenting right (if you create a new QObject/QWidget set the parent in the constructor). If the parent will be destructed, then the children will be too. In your main file, you can create the mainwindow on the stack, such that it will be destructed at the end of scope.

To call addToolbar you don't need this->, since it is a method of the class anyway.

The toolbar ptr should be a member to access it easily later on. But initialize it with nullptr (or NULL if you don't have c++11) in the initialization list of the constructor to know whether it is initialized or not.

The addToolBar call should work. A workaround would be to create a QToolBar on your own and add the pointer to the MainWindow using another addToolBar overload.