QGroupBox, QScrollArea, QFormLayout

[SGaist]

Hi,

As @JonB already wrote, QScrollArea is a container widget so 99% of the time you do not set a layout on it. You are in these 99%.

As already suggested, use a QWidget on which you apply the QFormLayout and set that widget on the QScrollArea.

You will then have the result you expect.

[SPlatten]

@SGaist , latest code:

        mpobjErrors = new QWidget(this);      //Wrapper/container for everything
        mpvbloErrors = new QVBoxLayout;       //Vertical layout for error messages
        mpsaErrors = new QScrollArea;         //Vertical layout to be scrollable
        mpsaErrors->setWidget(mpobjErrors);   //Add scroll area to container
        mpobjErrors->setLayout(mpvbloErrors); //Add vertical layout to container
        int intFixedHeight(fontMetrics().height() * MainWindow::mscuintErrorRows);
        mpsaErrors->setFixedHeight(intFixedHeight);  //Large enough for 3 rows of errors
        mpvbloErrors->addStretch(1);          
        QPushButton* pbtnAck(new QPushButton(tr("&Clear Errors")));
        QObject::connect(pbtnAck, &QPushButton::clicked,
            [this, pbtnAck]
            {
                mpobjErrors->setVisible(false);
            }
        );
        mpfrmloErrors = new QFormLayout;       //Layout for errors, time and cause
        mpvbloErrors->addLayout(mpfrmloErrors, 1); //Add form to vertical layout
        mpvbloErrors->addWidget(pbtnAck, 1, Qt::AlignHCenter); //Add button to container

The result from is:

I only want 3 lines to be displayed and the rest to be accessed using the scroll bar, but there is no scroll bar.

Its the QFormLayout that is used to display the error lines, the QVBoxLayout is used to contain the QFormLayout and the Clear Errors button at the bottom. I want the QFormLayout to be scrollable.

[edit]...:

    //Create container for errors panel
        mpobjErrors = new QWidget(this);
        mpvbloErrors = new QVBoxLayout;
        mpobjErrors->setLayout(mpvbloErrors);
    //Create a widget that contains the scrollable errors form
        QWidget* pobjFormErrorsContr(new QWidget(mpobjErrors));
        mpfrmloErrors = new QFormLayout;
        pobjFormErrorsContr->setLayout(mpfrmloErrors);
        int intFixedHeight(fontMetrics().height() * MainWindow::mscuintErrorRows);
        mpsaErrors = new QScrollArea;
        mpsaErrors->setWidget(pobjFormErrorsContr);
        mpsaErrors->setFixedHeight(intFixedHeight);
        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);

I thought perhaps an additional widget container would be required for the QFormLayout, didn't help.

[SGaist]

Why do you have a QVBoxLayou and a QFormLayout in mpobjErrors on the widget in your QScrollArea ?

The logic would rather be

-- QWidget ("this" in your sample code)
--- QVBoxLayout
---- QScrollArea (fixed height)
----- QWidget
------ QFormLayout
------- Dynamic number of widgets
---- QPushButton -> clear button

So you don't have to hunt for the clear button if you have lots of errors.

Note that depending on how many errors there might be limiting to three lines may not be the best user experience.

[SPlatten]

@SGaist , its supposed to be like this:

QWidget( mpobjErrors )
-- QVBoxLayout( mpvbloErrors )
----- QWidget( pobjFormErrorsContr )
-------- QScrollArea( fixed height )
-------- QFormLayout( mpfrmloErrors  )
----- QPushButton( pbtnAck )

Where only the QFormLayout is scrollable, but it isn't.

[JonB]

@SPlatten

----- QWidget( pobjFormErrorsContr )
-------- QScrollArea( fixed height )
-------- QFormLayout( mpfrmloErrors  )

But I/we already said that QScrollArea takes a setWidget(someWidget) for the thing it wants to scroll, which has to be a QWidget not a QLayout.

Also your QFormLayout is not anywhere descended from QScrollArea, it's a sibling, so it's not inside it, so it won't be subject to scrollability.

[SPlatten]

@JonB , see code above:

mpsaErrors = new QScrollArea;
mpsaErrors->setWidget(pobjFormErrorsContr);

[JonB]

@SPlatten
I see your code, my two comments apply to your "diagram", and comparing it to @SGaist's "diagram".

[SPlatten]

@JonB , what diagram are you referring to? the fixed height is just a setting, the parent of the QScrollArea is the widget its under.

[JonB]

@SPlatten said in QGroupBox, QScrollArea, QFormLayout:

what diagram are you referring to?

The 3 lines I quoted verbatim from your previous post. Whatever.

[SPlatten]

@JonB , yes and...haven't I explained what it means ?

[JonB]

@SPlatten
In @SGaist's "diagram" QFormLayout is descended (via a QWidget) from QScrollArea. In yours they are siblings, and then you say "Where only the QFormLayout is scrollable, but it isn't." If you think your diagram is clear and what you mean that's up to you.

[SPlatten]

@JonB

//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.