QGroupBox, QScrollArea, QFormLayout

[mpergand]

Assuming margins at set to zero:

pFormLayout=new QFormLayout;
pFormLayout->setContentsMargins(0,0,0,0);
pFormLayout->setSpacing(0);
pFormLayout->setHorizontalSpacing(10);

In the show event you can calculate 3 rows height like that:

void Widget::showEvent(QShowEvent* event)
{
    QWidget::showEvent(event);
    QLayoutItem * item=pFormLayout-> itemAt(0);
    int h=item->geometry().height();

    pScrollArea->setFixedHeight(h*3+2);

}

[SPlatten]

@mpergand , thank you

[mpergand]

@SPlatten
I assumed that the formLayout is not empty, unless the app will crash.

If you create one row in the constructor and want an empty form on show up, you can do:

QWidget::showEvent(event);
QLayoutItem* item=pFormLayout-> itemAt(0);
int h=item->geometry().height();
pScrollArea->setFixedHeight(h3+3);
pFormLayout->removeRow(0);

[WARNING]
Multi showEvent can occur, you need to add some flag to prevent that:

void Widget::showEvent(QShowEvent* event)
{
    static bool firstShow=true;

    QWidget::showEvent(event);
     
    if(firstShow)
        {
        QLayoutItem * item=pFormLayout-> itemAt(0);
        int h=item->geometry().height();
        pScrollArea->setFixedHeight(h*3+3);
        pFormLayout->removeRow(0);
        firstShow=false;
        }
}

[SPlatten]

@mpergand , this layout will only be displayed if there is content to display.

[JoeCFD]

@SPlatten Q
When you use font size to set item height, it is better to use some reference chars. That is what I do:
Rect bounding_rect = QFontMetrics( font ).tightBoundingRect( QString( "MWLPGHXYZmwlpghxyz" ) );
use bounding_rect.height();
And item height has to be a bit bigger than this height.

[SPlatten]

@mpergand , how is the showEvent connected and to which widget? I assume this is the MainWindow instance that this code is relevant to?

[mpergand]

@SPlatten
Here Widget is the top level object, but it does not have to be.

how is the showEvent connected

It's connected to nothing, it's a virtual method of QWidget.

[SPlatten]

@mpergand, can you post your full example source, showing the relationship between pScrollArea and pFormLayout ?

Thank you,

[mpergand]

Widget.h

#include <QWidget>

class QScrollArea;
class QFormLayout;

class Widget : public QWidget
    {
        Q_OBJECT
        
    public:
        
                explicit Widget(QWidget *parent = nullptr);
                
    private:
                      void  showEvent(QShowEvent* event);
               QScrollArea* pScrollArea;
               QFormLayout* pFormLayout;
};

Widget.cpp

Widget::Widget(QWidget *parent) : QWidget(parent)
{
    auto vLayout=new QVBoxLayout;
    setLayout(vLayout);
    
    pScrollArea=new QScrollArea;
    vLayout->addWidget(pScrollArea);
    
    auto sWidget=new QWidget;
    pScrollArea->setWidget(sWidget);
    pScrollArea->setWidgetResizable(true);
   
    pFormLayout=new QFormLayout;
    pFormLayout->setContentsMargins(0,0,0,1);
    pFormLayout->setSpacing(0);
    pFormLayout->setHorizontalSpacing(10);
    sWidget->setLayout(pFormLayout);

    // add one row for calculation in showEvent
    pFormLayout->addRow("", new QLabel());  

    vLayout->addWidget(new QPushButton("Clear"));
}

[SPlatten]

@mpergand , thank you, I'm creating a simple sample application, if I get it working in that then I can see what I need to do in my other application.

[SPlatten]

@mpergand , Thank you, works a treat...now to port to my main application:

    ui->setupUi(this);

    QVBoxLayout* pvbxLayout(new QVBoxLayout);
    mpsa = new QScrollArea;
    pvbxLayout->addWidget(mpsa);

    QWidget* pContainer(new QWidget);
    mpsa->setWidget(pContainer);
    int intFixedHeight(fontMetrics().height() * 3);
    mpsa->setFixedHeight(intFixedHeight);
    mpsa->setWidgetResizable(true);

    mpFormLayout = new QFormLayout;
    mpFormLayout->setContentsMargins(0,0,0,0);
    mpFormLayout->setSpacing(0);
    mpFormLayout->setHorizontalSpacing(10);
    pContainer->setLayout(mpFormLayout);

    for( int i=1; i<=10; i++ ) {
        mpFormLayout->addRow(QString::number(i),
                             new QLabel(QString("Hello World: %1").arg(i)));
    }
    pvbxLayout->addWidget(new QPushButton("HELLO"));
    ui->centralwidget->setLayout(pvbxLayout);