About QScroll Area

[franco.amato]

Hi to all, I attached a widget to a QScrollArea. Such widget has a moving timeline. I would keep the timeline visible when moving,
This mean that when the timeline come to the end of the widget the whole scrollarea should be shifted to the left. I don't know how to do it.

I hope to get help.

Best Regards,
Franco

[wysota]

Set value of the horizontal scroll bar of the scroll area to 0.

[franco.amato]

Set value of the horizontal scroll bar of the scroll area to 0.

Hi it doesn't work...when the time line comes at the end of the viewport it disappear and nothing happens

[wysota]

Please provide a minimal compilable example reproducing the problem.

[franco.amato]

Please provide a minimal compilable example reproducing the problem.

WaveWidget::WaveWidget( QWidget* parent /* = 0 */ )
: QWidget( parent ),
  m_wave(0),
  m_ZoomFactor( 1.0 )
{
   /* scroll area */
   QScrollArea* sa = new QScrollArea;
 
   sa->setWidgetResizable(true);
   QScrollBar *scrollBar = sa->horizontalScrollBar();
   scrollBar->setSliderDown( true );
   scrollBar->setValue(0);
   sa->setVerticalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
   sa->setHorizontalScrollBarPolicy(Qt::ScrollBarAlwaysOn);
 
   m_WaveDisplay = new WaveDisplay(sa->viewport());
   m_WaveDisplay->setSizePolicy(QSizePolicy::Preferred, QSizePolicy::Ignored);
   sa->setWidget( m_WaveDisplay );
 
 
  QHBoxLayout* hl = new QHBoxLayout();
  hl->addWidget(m_panel);
  hl->setSpacing( 0 );
  hl->addWidget(sa);
 
  QVBoxLayout* layout = new QVBoxLayout();
  layout->addLayout(hl);
  layout->addLayout(lo);
  setLayout(layout);
  setFocusPolicy( Qt::TabFocus );
}

WaveWidget::WaveWidget( QWidget* parent /* = 0 */ )
: QWidget( parent ),
  m_wave(0),
  m_ZoomFactor( 1.0 )
{
   /* scroll area */
   QScrollArea* sa = new QScrollArea;

   sa->setWidgetResizable(true);
   QScrollBar *scrollBar = sa->horizontalScrollBar();
   scrollBar->setSliderDown( true );
   scrollBar->setValue(0);
   sa->setVerticalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
   sa->setHorizontalScrollBarPolicy(Qt::ScrollBarAlwaysOn);

   m_WaveDisplay = new WaveDisplay(sa->viewport());
   m_WaveDisplay->setSizePolicy(QSizePolicy::Preferred, QSizePolicy::Ignored);
   sa->setWidget( m_WaveDisplay );


  QHBoxLayout* hl = new QHBoxLayout();
  hl->addWidget(m_panel);
  hl->setSpacing( 0 );
  hl->addWidget(sa);
 	
  QVBoxLayout* layout = new QVBoxLayout();
  layout->addLayout(hl);
  layout->addLayout(lo);
  setLayout(layout);
  setFocusPolicy( Qt::TabFocus );
}

To copy to clipboard, switch view to plain text mode 

m_WaveDisplay is a waveform display and when I click "play" a time line moves over it. When the timeline reach the end of the visible part it disappear on the right. I would shift the viewport() to keep visible ihe timeline.

I hope it's clear

[wysota]

That's neither compilable nor reproducing the problem...

Anyway, this works for me (and this is what I mean by a minimal compilable example):

#include <QtGui>
 
class ScrollArea : public QScrollArea {
public:
  ScrollArea() : QScrollArea(){}
protected:
  void timerEvent(QTimerEvent *te){
    int v = horizontalScrollBar()->value();
    int m = horizontalScrollBar()->maximum();
    if(v==m)
        horizontalScrollBar()->setValue(0);
    else
      horizontalScrollBar()->setValue(v+1);
  }
};
 
int main(int argc, char **argv){
  QApplication app(argc, argv);
  QLabel *label = new QLabel;
  QPixmap px(2048, 60);
  QLinearGradient grad(0,0,2048,0);
  grad.setColorAt(0, Qt::red);
  grad.setColorAt(1, Qt::blue);
  QPainter p(&px);
  p.fillRect(px.rect(), QBrush(grad));
  p.end();
  label->setPixmap(px);
  ScrollArea area;
  area.setWidget(label);
  area.show();
  area.startTimer(10);
  return app.exec();
}

#include <QtGui>

class ScrollArea : public QScrollArea {
public:
  ScrollArea() : QScrollArea(){}
protected:
  void timerEvent(QTimerEvent *te){
    int v = horizontalScrollBar()->value();
    int m = horizontalScrollBar()->maximum();
    if(v==m)
        horizontalScrollBar()->setValue(0);
    else
      horizontalScrollBar()->setValue(v+1);
  }
};

int main(int argc, char **argv){
  QApplication app(argc, argv);
  QLabel *label = new QLabel;
  QPixmap px(2048, 60);
  QLinearGradient grad(0,0,2048,0);
  grad.setColorAt(0, Qt::red);
  grad.setColorAt(1, Qt::blue);
  QPainter p(&px);
  p.fillRect(px.rect(), QBrush(grad));
  p.end();
  label->setPixmap(px);
  ScrollArea area;
  area.setWidget(label);
  area.show();
  area.startTimer(10);
  return app.exec();
}

To copy to clipboard, switch view to plain text mode 

[franco.amato]

That's neither compilable nor reproducing the problem...

Anyway, this works for me (and this is what I mean by a minimal compilable example):

#include <QtGui>
 
class ScrollArea : public QScrollArea {
public:
  ScrollArea() : QScrollArea(){}
protected:
  void timerEvent(QTimerEvent *te){
    int v = horizontalScrollBar()->value();
    int m = horizontalScrollBar()->maximum();
    if(v==m)
        horizontalScrollBar()->setValue(0);
    else
      horizontalScrollBar()->setValue(v+1);
  }
};
 
int main(int argc, char **argv){
  QApplication app(argc, argv);
  QLabel *label = new QLabel;
  QPixmap px(2048, 60);
  QLinearGradient grad(0,0,2048,0);
  grad.setColorAt(0, Qt::red);
  grad.setColorAt(1, Qt::blue);
  QPainter p(&px);
  p.fillRect(px.rect(), QBrush(grad));
  p.end();
  label->setPixmap(px);
  ScrollArea area;
  area.setWidget(label);
  area.show();
  area.startTimer(10);
  return app.exec();
}

#include <QtGui>

class ScrollArea : public QScrollArea {
public:
  ScrollArea() : QScrollArea(){}
protected:
  void timerEvent(QTimerEvent *te){
    int v = horizontalScrollBar()->value();
    int m = horizontalScrollBar()->maximum();
    if(v==m)
        horizontalScrollBar()->setValue(0);
    else
      horizontalScrollBar()->setValue(v+1);
  }
};

int main(int argc, char **argv){
  QApplication app(argc, argv);
  QLabel *label = new QLabel;
  QPixmap px(2048, 60);
  QLinearGradient grad(0,0,2048,0);
  grad.setColorAt(0, Qt::red);
  grad.setColorAt(1, Qt::blue);
  QPainter p(&px);
  p.fillRect(px.rect(), QBrush(grad));
  p.end();
  label->setPixmap(px);
  ScrollArea area;
  area.setWidget(label);
  area.show();
  area.startTimer(10);
  return app.exec();
}

To copy to clipboard, switch view to plain text mode 

Dear Wysota I solved my problem using ensureVisible routine of the QScrollArea http://doc.trolltech.com/4.6/qscroll...#ensureVisible givind periodically the position of the timeline and it works perfectly.
This routine is fantastic!!

Best Regards

[wysota]

That's the second time you "solved" your problem the wrong way. Keep doing that and at some point everything will fall apart.

[franco.amato]

That's the second time you "solved" your problem the wrong way. Keep doing that and at some point everything will fall apart.

Why wrong way? Seems work well. I don't have to set to zero the scroll bar, I would keep visible the timeline

[wysota]

Why wrong way? Seems work well.

Many things seem well but you shouldn't use them as at some point the combination of things that seem to work fell will blow up into your face.

I don't have to set to zero the scroll bar,

Honestly, you don't have to do anything...

I would keep visible the timeline

Did you run my example? Did you see the gradient vanishing after reaching the end? Maybe things are already exploding in your face...

[franco.amato]

Sorry but nothing is exploding in my face and yes I run your example.
I think you should speak in a different way as administrator without ridicole the work of other developers.
Maybe I'm not a Qt expert, my field is another and if I ask for help here is to learn and improve my Qt.

Best Regards