Question

I would like to force an expanding space in my QFormLayout, but no matter what QFormLayout only uses the QSpaceItem::sizeHint(). Does anyone know a way around this, or the proper way to handle this?

---

MyWidget::MyWidget(QWidget *parent) : QWidget(parent)
{
   SetupLayout();
}

void MyWidget::SetupLayout()
{
   QFormLayout * layout = new QFormLayout();

   layout->addRow("Something1", new QComboBox());
   layout->addRow("Something2", new QSpinBox());

   //Spacer
   layout->addItem(new QSpacerItem(0,10, QSizePolicy::Expanding, QSizePolicy::Expanding));

   layout->addRow(QPushButton("Something3"));

   setLayout(layout);
}

Answer 1

So there were a few different issues:

1. QFormLayout do not expand like other layouts. My widgets (a few of them) were being placed into a QFormLayout. This prevented them from expanding. I switched my main parent layout from QFormLayout to QVBoxLayout. This made me have to use QLayout::setAlignment(Qt::AlignTop)
2. This fixed a few problems with a few of my other widgets not expanding. However these widgets used QVBoxLayout. The widget above uses a QFormLayout. To get this expand, I had to use the following line in my QSpacerItem:

QSpacerItem * my_spacer = new QSpacerItem(0,1000, QSizePolicy::Expanding, QSizePolicy::Expanding);

---

I am supplying some example code. The goal is to show the hierarchy, and where QFormLayout would cause trouble.

Example code:

//A main Widget class
void SetupLayout()
{
   QHBoxLayout * main_layout = new QHBoxLayout();

   main_layout->addWidget(Some_Widget);

   //Create a control widget
   control_widget = new QWidget();  // IMPORTANT control_widget is a member
   QVBoxLayout * layout = new QVBoxLayout(); //IMPORTANT!!!! - Here it was QFormLayout

   layout->setAlignment(Qt::AlignTop); //IMPORTANT - Needed this after switching to QVBoxLayout

   layout->addWidget(new QComboBox("stuff")); //Some combo box
   control_widget->setLayout(layout);

   main_layout->addWidget(control_widget);
}

//Later on, we have a "Put a new widget in the control area" task
void NewControlArea()
{
   if(current_control)
      control_widget->removeWidget(current_control);  //current_control is a member variable

   current_control = new MyWidget();  //FROM ABOVE
   control_widget->addWidget(current_control);
}

If MyWidget uses a QFormLayout, things are not expanded unless I add spacers with size hints. However, if MyWidget uses a QVBoxLayout, any QWidgets inside it are expanded correctly.