QScrollArea as central widget problem

Perdrix

As was suggested on another thread https://forum.qt.io/topic/159300/qdockwidget-oddness, I tried to add a QScrollArea to my application:

Old code:

	ZTRACE_RUNTIME("Creating stackedWidget");
	stackedWidget = new QStackedWidget(this);
	stackedWidget->setObjectName("stackedWidget");
	setCentralWidget(stackedWidget);

	ZTRACE_RUNTIME("Creating Stacking Panel");
	stackingDlg = new DSS::StackingDlg(this, pictureList);
	stackingDlg->setObjectName("stackingDlg");

	ZTRACE_RUNTIME("Adding Stacking Panel to stackedWidget");
	stackedWidget->addWidget(stackingDlg);
	
	ZTRACE_RUNTIME("Creating Processing Panel");
	processingDlg = new DSS::ProcessingDlg(this);
	processingDlg->setObjectName("processingDlg");

	ZTRACE_RUNTIME("Adding Processing Panel to stackedWidget");
	stackedWidget->addWidget(processingDlg);

	stackedWidget->setSizePolicy(QSizePolicy::Expanding, QSizePolicy::Expanding);

new code:

	ZTRACE_RUNTIME("Creating scrollarea");
	scrollArea = new QScrollArea(this);
	scrollArea->setObjectName("scrollArea");
	scrollArea->setHorizontalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
	setCentralWidget(scrollArea);

	ZTRACE_RUNTIME("Creating stackedWidget");
	stackedWidget = new QStackedWidget(this);
	stackedWidget->setObjectName("stackedWidget");
	scrollArea->setWidget(stackedWidget);
	scrollArea->ensureWidgetVisible(stackedWidget);

	ZTRACE_RUNTIME("Creating Stacking Panel");
	stackingDlg = new DSS::StackingDlg(this, pictureList);
	stackingDlg->setObjectName("stackingDlg");

	ZTRACE_RUNTIME("Adding Stacking Panel to stackedWidget");
	stackedWidget->addWidget(stackingDlg);
	
	ZTRACE_RUNTIME("Creating Processing Panel");
	processingDlg = new DSS::ProcessingDlg(this);
	processingDlg->setObjectName("processingDlg");

	ZTRACE_RUNTIME("Adding Processing Panel to stackedWidget");
	stackedWidget->addWidget(processingDlg);

	stackedWidget->setSizePolicy(QSizePolicy::Expanding, QSizePolicy::Expanding);

The problem is that nothing is visible in the central widget area? I expected the stacked widget with its owned widgets to be there.

What have I missed or misunderstood?

Perdrix

The following works as I want which was to use a scroll bar when the widgets contained within the stacked widget hit their minimum size, and the user wants to resize the frame window smaller then would otherwise work.

ZTRACE_RUNTIME("Creating stackedWidget");
stackedWidget = new QStackedWidget(this);
stackedWidget->setObjectName("stackedWidget");
scrollArea->setWidget(stackedWidget);
scrollArea->ensureWidgetVisible(stackedWidget);
scrollArea->setWidgetResizable(true);
scrollArea->setGeometry(0, 0, 500, 500);
scrollArea->setMinimumHeight(300);

David

Pl45m4

@Perdrix said in QScrollArea as central widget problem:

I tried to add a QScrollArea to my application:

There's nothing wrong with adding a QScrollArea as central widget.
Works for me for any standard widget.

I suspect your widget(s) is/are there, but you just don't see them because they are too small.

Try

stackedWidget->setGeometry(0, 0, 1000, 1000);

Do you see something now?

And how about this code?

#include <QApplication>
#include <QMainWindow>
#include <QPushButton>
#include <QHBoxLayout>
#include <QScrollArea>
#include <QStackedWidget>
#include <QDebug>

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
    QMainWindow w;

    QWidget widget(&w);
    QPushButton pb("CLICK");
    widget.setObjectName("widget");
    widget.setStyleSheet("QWidget#widget { background-color: blue; }");
    QHBoxLayout layout(&widget);
    widget.setLayout(&layout);
    layout.addWidget(&pb);
    QScrollArea *area = new QScrollArea(&w);
    QStackedWidget *stack = new QStackedWidget(area);
//    stack->setGeometry(0, 0, 500, 500);
    stack->addWidget(&widget);
    stack->setSizePolicy(QSizePolicy::Expanding, QSizePolicy::Expanding);

    area->ensureWidgetVisible(stack);
    area->setWidget(stack);

    w.setCentralWidget(area);

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

If this works, there's something wrong with your DSS:: classes.

Perdrix

The setGeometry call worked to get it to display but the dimensions of the widgets within the stacked widget then didn't resize as the main window was re-sized. I need to think again how to handle the problem of one of the widgets in the stacked widget set being a bit larger than desired (so that it creates sizing anomalies on small screens).

D.

Pl45m4

@Perdrix said in QScrollArea as central widget problem:

but the dimensions of the widgets within the stacked widget then didn't resize as the main window was re-sized

Then you are using QScrollArea wrong... or expect something different from it.
What's the point of scrollbars or a scrollable area in first place, if the widget would resize with the window?!

QScrollArea is for displaying large (static) content like huge images through a small(er) viewport.
Whenever you resize the window around it, the viewport (visible area) changes... not the scroll area's content widget.

Perdrix

The following works as I want which was to use a scroll bar when the widgets contained within the stacked widget hit their minimum size, and the user wants to resize the frame window smaller then would otherwise work.

ZTRACE_RUNTIME("Creating stackedWidget");
stackedWidget = new QStackedWidget(this);
stackedWidget->setObjectName("stackedWidget");
scrollArea->setWidget(stackedWidget);
scrollArea->ensureWidgetVisible(stackedWidget);
scrollArea->setWidgetResizable(true);
scrollArea->setGeometry(0, 0, 500, 500);
scrollArea->setMinimumHeight(300);

David