[SOLVED] QScrollArea: Vertical scroll only.

ultim8

Hello,

I'm trying to use a QScrollArea where only the vertical scrollbar is in use.

I've set setHorizontalScrollBarPolicy(Qt::ScrollBarAlwaysOff);

But that simply makes the internal widgets clip on the right side of the screen.

What I've done so far is ovride the resizeEvent and set:
widget()->setMinimumWidth(event->size().width())

This does the trick a lot of the time... but if the internal widgets needs a size greater then what the resize event is giving then the internal widgets start drawing on top of each other.

Does anyone have any ideas of how to resolve this?

leon.anavi

Try to disable the horizontal scroll and enable the vertical scroll if needed usi the following methods of "QAbstractScrollArea":http://doc.qt.nokia.com/4.8-snapshot/qabstractscrollarea.html#verticalScrollBarPolicy-prop

@
QAbstractScrollArea::setHorizontalScrollBarPolicy( Qt::ScrollBarAlwaysOff )
QAbstractScrollArea::setVerticalScrollBarPolicy( Qt::ScrollBarAsNeeded)
@

ultim8

Sigh...

In my original message I have already mentioned that I did exactly that already... but that is not enough.

What I want:

The QScrollArea should scroll vertically (as it does normally).

Horizontally it should behave exactly like a QWidget

-meaning internal widgets resize to fit it's available space
-also it is not allowed to resize smaller then the internal widgets permit.

ultim8

Found a solution! simply look for resize events for the scrollAreaWithContents widgets and set the scrollArea's minimum width to the scrollAreaWithContents minimumSizeHint().with():

@VerticalScrollArea::VerticalScrollArea(QWidget *parent)
: QScrollArea(parent)
{
setWidgetResizable(true);
setFrameStyle(QFrame::NoFrame);
setHorizontalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
setVerticalScrollBarPolicy(Qt::ScrollBarAsNeeded);
m_scrollAreaWidgetContents = new QWidget(this);
m_scrollAreaWidgetContents->setSizePolicy(QSizePolicy::Preferred, QSizePolicy::Preferred);
QVBoxLayout *baseLayout = new QVBoxLayout(m_scrollAreaWidgetContents);
setWidget(m_scrollAreaWidgetContents);
m_scrollAreaWidgetContents->installEventFilter(this);
}

bool VerticalScrollArea::eventFilter(QObject *o, QEvent *e)
{
if(o == m_scrollAreaWidgetContents && e->type() == QEvent::Resize)
setMinimumWidth(m_scrollAreaWidgetContents->minimumSizeHint().width() + verticalScrollBar()->width());

return false;
}@

ostlerc

Thanks for solving this problem! However, unless your minimum size changes on resize events you will only need to set this once after a show event.

galinette

Thanks for the solution!

By the way, this is close to be a bug. A QScrollArea with horizontal bars switched off should set its minimum width by considering the minimum width of the contents widget, no?

mstone1959

Hello,

I'm fairly new to Qt and I would like to know how I implement the VerticalScrollArea class to correct the problem?

ultim8

[quote author="mstone1959" date="1389726822"]Hello,

I'm fairly new to Qt and I would like to know how I implement the VerticalScrollArea class to correct the problem?[/quote]

You will want to create a new class "VerticalScrollArea" derived off of QScrollArea.

header:
@#ifndef VERTICALSCROLLAREA_H
#define VERTICALSCROLLAREA_H

#include <QScrollArea>

class VerticalScrollArea : public QScrollArea
{
Q_OBJECT
public:
explicit VerticalScrollArea(QWidget *parent = 0);

virtual bool eventFilter(QObject *o, QEvent *e);

};

#endif // VERTICALSCROLLAREA_H@

Implementation:
@#include <QEvent>
#include <QScrollBar>

#include "verticalscrollarea.h"

VerticalScrollArea::VerticalScrollArea(QWidget *parent) :
QScrollArea(parent)
{
setWidgetResizable(true);
setHorizontalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
setVerticalScrollBarPolicy(Qt::ScrollBarAsNeeded);
}

bool VerticalScrollArea::eventFilter(QObject *o, QEvent *e)
{
// This works because QScrollArea::setWidget installs an eventFilter on the widget
if(o && o == widget() && e->type() == QEvent::Resize)
setMinimumWidth(widget()->minimumSizeHint().width() + verticalScrollBar()->width());

return QScrollArea::eventFilter(o, e);
}
@

trusktr

[quote author="galinette" date="1360135272"]Thanks for the solution!

By the way, this is close to be a bug. A QScrollArea with horizontal bars switched off should set its minimum width by considering the minimum width of the contents widget, no?[/quote]

I don't think so. I think setting the horizontal scroll bar to off should simply not show a horizontal scroll bar (but that doesn't mean the area can't be scrolled, e.g. with touch and drag). Changing the width of the scroll area should be a separate step if the developer so desires.

Jacques L.

Although old, this topic saved me time. So here are my two cents here. I change the constructor to this to support one-finger scrolling on Android (didn't try for iOS yet):

CVScrollArea::CVScrollArea(QWidget *parent)
   : QScrollArea(parent)
{
   setWidgetResizable(true);
   setHorizontalScrollBarPolicy(Qt::ScrollBarAlwaysOff);

// One-finger swipe/scroll while default in Qt is 3-fingers!
   QScroller::grabGesture(this->viewport(), QScroller::LeftMouseButtonGesture);

// No scroll bar for Android (and probably iOS)
#ifndef Q_OS_ANDROID
      this->setVerticalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
#else
      this->setVerticalScrollBarPolicy(Qt::ScrollBarAsNeeded);
#endif
}

viteo

Hello from 2022.
Used all my google-fu to find this answer. Thank you!
I confirm that there is still no standard QVerticalScroll, you have to implement it yourself with overriding eventFilter.

p.s.
...but the eventFilter() get a lot of calls from everythin (mouse, activation, resize etc)
I suggest to override resizeEvent(). Here is my approach:

HEADER:

protected:
    void resizeEvent(QResizeEvent *);

SOURCE:

void ClassName::resizeEvent(QResizeEvent* event)
{
    setMinimumWidth(widget()->minimumSizeHint().width() + verticalScrollBar()->width());
    QScrollArea::resizeEvent(event);
}

Vaquita Tim

Every couple of years this comes up...

Certainly setMinimumWidth() is key - it needs to fit the size of the scrolled widget().

In my derived class I actually connected a slot to the horizontal scroll bar, which changes if the widget() changes width

connect( horizontalScrollBar(), &QAbstractSlider::rangeChanged, this, &CVerticalScrollArea::ResetMinWidth );

then I calculate the minumum width bearing in mind the frame width. I do the same for the minimumSizeHint too (although maybe this is not required).

QSize CVerticalScrollArea::minimumSizeHint() const
{
	QSize MinSize( QScrollArea::minimumSizeHint() );
	const QWidget * pWidget( widget() );
	if( pWidget )
	{
		const int FrameWidth( 2 * frameWidth() );
		const int TotalWidth( pWidget->minimumSizeHint().rwidth() + FrameWidth );
		if( TotalWidth > MinSize.width() )
			MinSize.setWidth( TotalWidth );
	}
	return MinSize;
}