QGroupBox, QScrollArea, QFormLayout

SPlatten

//Create container for errors panel
        mpobjErrors = new QWidget(this);
        mpvbloErrors = new QVBoxLayout;
        mpobjErrors->setLayout(mpvbloErrors);
        mpsaErrors = new QScrollArea;
        int intFixedHeight(fontMetrics().height() * MainWindow::mscuintErrorRows);
        mpsaErrors->setFixedHeight(intFixedHeight);
    //Create a widget that contains the scrollable errors form
        QWidget* pobjFormErrorsContr(new QWidget);
        mpsaErrors->setWidget(pobjFormErrorsContr);
        mpfrmloErrors = new QFormLayout;
        pobjFormErrorsContr->setLayout(mpfrmloErrors);
        mpvbloErrors->addWidget(pobjFormErrorsContr, 1, Qt::AlignHCenter);
    //Create a push button for acknowledging and clearing errors panel
        QPushButton* pbtnAck(new QPushButton(tr("&Clear Errors")));
        mpvbloErrors->addWidget(pbtnAck, 1, Qt::AlignHCenter);
        QObject::connect(pbtnAck, &QPushButton::clicked,
            [this, pbtnAck]
            {
                mpobjErrors->setVisible(false);
            }
        );
    //Default to hidden until errors are available to display
        mpobjErrors->setVisible(false);

From the above the structure should be:

QWidget
-- QVBoxLayout
----- QScrollArea, with fixed height to show 3 rows
------- QWidget
---------- QFormLayout
------ QPushButton

The image of this output:

The form layout needs to be the full width of the QVBoxLayout and should be just 3 rows as the image shows it isn't.

JonB

@SPlatten
Your "diagram" now looks like @SGaist's, so I am happy.

I have played with scroll areas all morning for you, and I have had enough! Play with this:

#include "widget.h"

#include <QApplication>
#include <QScrollArea>
#include <QBoxLayout>
#include <QPushButton>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    Widget w;

    QVBoxLayout layout0;
    w.setLayout(&layout0);

    QScrollArea scrollArea(&w);
    layout0.addWidget(&scrollArea);
    QWidget container(&scrollArea);
    scrollArea.setWidget(&container);
    QVBoxLayout layout;
    container.setLayout(&layout);
    for (int i = 0; i < 10; i++)
        layout.addWidget(new QPushButton);

    scrollArea.setVerticalScrollBarPolicy(Qt::ScrollBarPolicy::ScrollBarAsNeeded);
    scrollArea.setFixedHeight(100);
    scrollArea.setWidgetResizable(true);

    w.show();
    return a.exec();
}

Note the scrollArea.setWidgetResizable(true);. Without that I don't actually see any buttons. Is that what you are missing?

Don't ask me about Qt layouts/size policies etc., I have always found them about as intuitive as a duck-billed platypus, I play till I get what I want.

SPlatten

@JonB , thank you, however its missing the QFormLayout which is required, see my post before you post.

Edited code, still doesn't work.

    //Create container for errors panel
        mpobjErrors = new QWidget(this);
        mpvbloErrors = new QVBoxLayout;
        mpobjErrors->setLayout(mpvbloErrors);
    //Create scroll area
        mpsaErrors = new QScrollArea(mpobjErrors);
    //Create a widget that contains the scrollable errors form
        QWidget* pobjFormErrorsContr(new QWidget(mpsaErrors));
    //Set-up scroll area
        mpsaErrors->setVerticalScrollBarPolicy(Qt::ScrollBarAsNeeded);
        int intFixedHeight(fontMetrics().height() * MainWindow::mscuintErrorRows);
        mpsaErrors->setWidget(pobjFormErrorsContr);
        mpsaErrors->setFixedHeight(intFixedHeight);
        mpsaErrors->setWidgetResizable(true);
        mpfrmloErrors = new QFormLayout(pobjFormErrorsContr);
        mpvbloErrors->addWidget(pobjFormErrorsContr, 1, Qt::AlignHCenter);//addLayout(mpfrmloErrors, 1);//
    //Create a push button for acknowledging and clearing errors panel
        QPushButton* pbtnAck(new QPushButton(tr("&Clear Errors")));
        mpvbloErrors->addWidget(pbtnAck, 1, Qt::AlignHCenter);
        QObject::connect(pbtnAck, &QPushButton::clicked,
            [this, pbtnAck]
            {
                mpobjErrors->setVisible(false);
            }
        );

JonB

@SPlatten
I found I had to put in scrollArea.setWidgetResizable(true); to make it respect the height. You are saying it still does not. I assume you have verified the value for fontMetrics().height() * MainWindow::mscuintErrorRows. You can put a QFormLayout into my sample code in place of QVBoxLayout layout;, I can't see why that would behave any differently vertically.

SPlatten

@JonB , just to verify:

int intFontHeight(fontMetrics().height()),
    intFixedHeight(intFontHeight * MainWindow::mscuintErrorRows);

intFontHeight is 13
MainWindow::mscuintErrorRows is 3
intFixedHeight is 39

Clearly setFixedHeight on mpsaErrors is not having the desired effect.

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);