Auto scroll down in QScrollArea

[EricF]

Hi, I've made a search and found lots of answer but I still can't get it to work. I'm toying with the scroll area in which I want to add widget to it dynamically and I want the scroll area to ensure the las widget is always visible.

I use a widget in which I use a QVBoxLayout and then set this widget in the scroll area. I can see my stuff but it always scrolls to the next to last one when I use ensureWidgetVisible. I traced this method and the size hint returned seems ok. Here's my test code:

#include <QApplication>
#include <QtGui>
 
#include "MainWidget.h"
 
int main( int argc, char* argv[] )
{
	QApplication app( argc, argv );
 
	// Put your own widget here.
	MainWidget* w = new MainWidget();
	w->show();
 
	return app.exec();
}

#include <QApplication>
#include <QtGui>

#include "MainWidget.h"

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

	// Put your own widget here.
	MainWidget* w = new MainWidget();
	w->show();

	return app.exec();
}

To copy to clipboard, switch view to plain text mode 

#pragma once
 
#include <QtGui>
 
class MainWidget : public QWidget
{
	Q_OBJECT
 
public:
	MainWidget( QWidget* parent = 0 );
 
 
public slots:
	void OnNewElement();
 
protected slots:
	void ScrollToEnd();
 
protected:
	QScrollArea* mScrollArea;
	QWidget* mInternalWidget;
	QVBoxLayout* mInternalLayout;
	QWidget* mLastChild;
};

#pragma once

#include <QtGui>

class MainWidget : public QWidget
{
	Q_OBJECT

public:
	MainWidget( QWidget* parent = 0 );

	
public slots:
	void OnNewElement();

protected slots:
	void ScrollToEnd();

protected:
	QScrollArea* mScrollArea;
	QWidget* mInternalWidget;
	QVBoxLayout* mInternalLayout;
	QWidget* mLastChild;
};

To copy to clipboard, switch view to plain text mode 

#include "MainWidget.h"
 
MainWidget::MainWidget( QWidget* parent ) : QWidget(parent)
{
	QHBoxLayout* layout = new QHBoxLayout(this);
	setLayout( layout );
 
	mScrollArea = new QScrollArea(this);
	layout->addWidget( mScrollArea );
 
	mInternalWidget = new QWidget(mScrollArea);
	mInternalLayout = new QVBoxLayout(mInternalWidget);
	mInternalWidget->setLayout(mInternalLayout);
 
	QWidget* element = NULL;
	for (int i=0; i<20; ++i)
	{
		QString name = QString("Base Element %0").arg(i);
		element = new QWidget( mInternalWidget );
		element->setFixedSize( 200,20 );
 
		element->setAutoFillBackground( true );
		QPalette p = element->palette();
		p.setColor( QPalette::Window, QColor(255,0,255) );
		element->setPalette(p);
 
		mInternalLayout->addWidget( element );
	}
 
	mScrollArea->setWidget( mInternalWidget );
	mScrollArea->setWidgetResizable(true);
	mScrollArea->verticalScrollBar()->setSingleStep( 20 );
 
	QPushButton* b = new QPushButton( "Add new element" );
	connect( b, SIGNAL(clicked()), this, SLOT(OnNewElement()) );
 
	layout->addWidget( b );
}
 
void MainWidget::OnNewElement()
{
	static int count = 0;
	QString name = QString("New Element %0").arg(count++);
	QLabel* element = new QLabel( name );
	element->setFixedSize( 100, 20 );
 
	element->setAutoFillBackground( true );
	QPalette p = element->palette();
	p.setColor( QPalette::Window, QColor(255,0,0) );
	element->setPalette(p);
 
	mInternalLayout->addWidget( element );
	mLastChild = element;
	QTimer::singleShot( 5, this, SLOT(ScrollToEnd()) );
}
 
void MainWidget::ScrollToEnd()
{
	//mScrollArea->verticalScrollBar()->setValue( mScrollArea->verticalScrollBar()->maximum() );
	mScrollArea->ensureWidgetVisible( mLastChild );
}

#include "MainWidget.h"

MainWidget::MainWidget( QWidget* parent ) : QWidget(parent)
{
	QHBoxLayout* layout = new QHBoxLayout(this);
	setLayout( layout );

	mScrollArea = new QScrollArea(this);
	layout->addWidget( mScrollArea );

	mInternalWidget = new QWidget(mScrollArea);
	mInternalLayout = new QVBoxLayout(mInternalWidget);
	mInternalWidget->setLayout(mInternalLayout);

	QWidget* element = NULL;
	for (int i=0; i<20; ++i)
	{
		QString name = QString("Base Element %0").arg(i);
		element = new QWidget( mInternalWidget );
		element->setFixedSize( 200,20 );

		element->setAutoFillBackground( true );
		QPalette p = element->palette();
		p.setColor( QPalette::Window, QColor(255,0,255) );
		element->setPalette(p);
		
		mInternalLayout->addWidget( element );
	}

	mScrollArea->setWidget( mInternalWidget );
	mScrollArea->setWidgetResizable(true);
	mScrollArea->verticalScrollBar()->setSingleStep( 20 );

	QPushButton* b = new QPushButton( "Add new element" );
	connect( b, SIGNAL(clicked()), this, SLOT(OnNewElement()) );

	layout->addWidget( b );
}

void MainWidget::OnNewElement()
{
	static int count = 0;
	QString name = QString("New Element %0").arg(count++);
	QLabel* element = new QLabel( name );
	element->setFixedSize( 100, 20 );
	
	element->setAutoFillBackground( true );
	QPalette p = element->palette();
	p.setColor( QPalette::Window, QColor(255,0,0) );
	element->setPalette(p);

	mInternalLayout->addWidget( element );
	mLastChild = element;
	QTimer::singleShot( 5, this, SLOT(ScrollToEnd()) );
}

void MainWidget::ScrollToEnd()
{
	//mScrollArea->verticalScrollBar()->setValue( mScrollArea->verticalScrollBar()->maximum() );
	mScrollArea->ensureWidgetVisible( mLastChild );
}

To copy to clipboard, switch view to plain text mode 

Calling ensureWidgetVisible from the OnNewElement slot does not work and I suspected that is was because the layout had not been calculated yet so I tried a singleShot timer to do the scroll. It works for the first 100 or so elements but after that, it scrolls to the next to last element again.

I know we're on the 24th but you know the drill, coders almost always work

[ntp]

Did you try setting the margins = 0?

mScrollArea->ensureWidgetVisible( mLastChild , 0, 0);

mScrollArea->ensureWidgetVisible( mLastChild , 0, 0);

To copy to clipboard, switch view to plain text mode 

[EricF]

Yeah tried it too but it doesn't work either.