Clearing and repopulating a QFormLayout - c++

Question

I'm trying to set up a QFormLayout so that some buttons show or hide the part below them, and using setHidden on the widgets I want to hide is resulting in a bad layout due to the form padding still showing.
So I tried this:
#include <QApplication>
#include <QCheckBox>
#include <QLabel>
#include <QFormLayout>
#include <QMainWindow>
class MainWindow : public QMainWindow
{
Q_OBJECT
QCheckBox checkA;
QFormLayout * m_formLayout;
QWidget * m_widget;
public:
explicit MainWindow(QWidget *parent = 0) :
QMainWindow(parent),
m_formLayout(0L),
m_widget(0L)
{
populate();
connect(&checkA, &QCheckBox::stateChanged, this, &MainWindow::populate);
}
virtual ~MainWindow() { clear(); }
bool doesOwnObject(void * it) const
{
return (uintptr_t)this <= (uintptr_t)it && (uintptr_t)it < (uintptr_t)(this+1);
}
void clear()
{
if(m_formLayout)
{
QLayoutItem *child;
while ((child = m_formLayout->takeAt(0)) != 0)
{
QLayout * layout = child->layout();
QSpacerItem * spacer = child->spacerItem();
QWidget * widget = child->widget();
if(layout && !doesOwnObject(layout)) delete layout;
if(spacer && !doesOwnObject(spacer)) delete spacer;
if(widget && !doesOwnObject(widget)) delete widget;
}
delete m_formLayout;
m_formLayout = 0L;
}
}
void populate()
{
if(m_widget) { clear(); return; }
m_widget = new QWidget(this);
setCentralWidget(m_widget);
m_formLayout = new QFormLayout(m_widget);
m_formLayout->addRow(tr("Show Check Box B:"), &checkA);
}
};
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
MainWindow w;
w.show();
return a.exec();
}
But that doesn't seem to work as clear() doesn't seem to be actually depopulating the form layout. The widgets remain where they were before the QFormLayout was deleted. And if m_widget is deleted then the program will crash as it tries to delete checkA, because checkA has not been removed from the now deleted form.
How do I fix this?

Answer 1

I have come to a solution that has the desirable (or what I understood) behavior. However, I've moved everything to pointers (since is what I am used to with Qt).
Header file:
#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <QCheckBox>
#include <QLayoutItem>
#include <QFormLayout>
#include <QMainWindow>
#include <QLabel>
class MainWindow : public QMainWindow
{
Q_OBJECT
QCheckBox *checkA, *checkB;
QLabel *labelA, *labelB, *labelC;
QFormLayout * m_formLayout;
public:
explicit MainWindow(QWidget *parent = 0);
virtual ~MainWindow();
void clear();
public slots:
void populate();
};
#endif // MAINWINDOW_H
cpp file:
#include "mainWindow.h"
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent)
{
QWidget * centralWidget = new QWidget(this);
setCentralWidget(centralWidget);
m_formLayout = new QFormLayout(centralWidget);
checkA = new QCheckBox;
labelA = new QLabel("Show Check Box B:");
connect(checkA, &QCheckBox::stateChanged, this, &MainWindow::populate);
int row = 0;
m_formLayout->insertRow(row++, labelA, checkA);
checkB = new QCheckBox;
labelB = new QLabel("Check Box B:");
m_formLayout->insertRow(row++, labelB, checkB);
labelC = new QLabel("Bottom label");
m_formLayout->insertRow(row++,labelC);
populate();
}
MainWindow::~MainWindow() {
}
void MainWindow::clear()
{
if (!checkA->isChecked())
{
checkB->hide();
labelB->hide();
}
}
void MainWindow::populate()
{
clear();
if(checkA->isChecked())
{
checkB->show();
labelB->show();
}
}

Answer 2

Solution:
void clear()
{
QLayoutItem *child;
while ((child = m_formLayout->takeAt(0)) != 0)
{
QLayout * layout = child->layout();
QSpacerItem * spacer = child->spacerItem();
QWidget * widget = child->widget();
if(layout && !doesOwnObject(layout)) delete layout;
if(spacer && !doesOwnObject(spacer)) delete spacer;
if(widget)
{
if(doesOwnObject(widget)) widget->setParent(0L);
else delete widget;
}
}
}
setParent had to be called.