How to get scrollbars in QTreeWidget

**jorma** · 3rd May 2006, 20:04

I'll answer myself now that I found out how to do it...

in order to get everything right, it is enough to say in MyTreeWidget's constructor also

setHorizontalScrollBarPolicy( Qt::ScrollBarAlwaysOn);
setVerticalScrollBarPolicy( Qt::ScrollBarAlwaysOn);

connect(this->horizontalScrollBar(), SIGNAL(actionTriggered(int)),
this, SLOT(updateColumnWidth()));
connect(this->verticalScrollBar(), SIGNAL(actionTriggered(int)),
this, SLOT(updateColumnWidth()));

**minorpan** · 5th May 2006, 06:15

Dear Jorma:

I have tried to reconstruct your problem by adding the following code to function main().

#include "MyTreeWidget.h"
int main(int argc, char* argv[])

QApplication app(argc, argv);
MyTreeWidget widget;
QTreeWidgetItem* pItem;
pItem = new QTreeWidgetItem(&widget, QStringList("aaaaaaaaaaaaaaaaaaaaaaa"));
pItem = new QTreeWidgetItem(pItem, QStringList("aaaaaaaaaaaaaaaaaaaaaaa"));
pItem = new QTreeWidgetItem(pItem, QStringList("aaaaaaaaaaaaaaaaaaaaaaa"));
pItem = new QTreeWidgetItem(pItem, QStringList("aaaaaaaaaaaaaaaaaaaaaaa"));
pItem = new QTreeWidgetItem(pItem, QStringList("aaaaaaaaaaaaaaaaaaaaaaa"));
pItem = new QTreeWidgetItem(pItem, QStringList("aaaaaaaaaaaaaaaaaaaaaaa"));
pItem = new QTreeWidgetItem(pItem, QStringList("aaaaaaaaaaaaaaaaaaaaaaa"));
pItem = new QTreeWidgetItem(&widget, QStringList("aaaaaaaaaaaaaaaaaaaaaaa"));
pItem = new QTreeWidgetItem(pItem, QStringList("aaaaaaaaaaaaaaaaaaaaaaa"));
pItem = new QTreeWidgetItem(pItem, QStringList("aaaaaaaaaaaaaaaaaaaaaaa"));
pItem = new QTreeWidgetItem(pItem, QStringList("aaaaaaaaaaaaaaaaaaaaaaa"));
pItem = new QTreeWidgetItem(pItem, QStringList("aaaaaaaaaaaaaaaaaaaaaaa"));
pItem = new QTreeWidgetItem(pItem, QStringList("aaaaaaaaaaaaaaaaaaaaaaa"));
pItem = new QTreeWidgetItem(pItem, QStringList("aaaaaaaaaaaaaaaaaaaaaaa"));
pItem = new QTreeWidgetItem(&widget, QStringList("aaaaaaaaaaaaaaaaaaaaaaa"));
pItem = new QTreeWidgetItem(pItem, QStringList("aaaaaaaaaaaaaaaaaaaaaaa"));
pItem = new QTreeWidgetItem(pItem, QStringList("aaaaaaaaaaaaaaaaaaaaaaa"));
pItem = new QTreeWidgetItem(pItem, QStringList("aaaaaaaaaaaaaaaaaaaaaaa"));
pItem = new QTreeWidgetItem(pItem, QStringList("aaaaaaaaaaaaaaaaaaaaaaa"));
pItem = new QTreeWidgetItem(pItem, QStringList("aaaaaaaaaaaaaaaaaaaaaaa"));
pItem = new QTreeWidgetItem(pItem, QStringList("aaaaaaaaaaaaaaaaaaaaaaa"));
widget.show();

}

With my original constructor of MyTreeWidget and your implementation of resizeEvent(), it works well, and the scroll bars do not flicker after the window is resized even if all items are expanded.
So could you please let me see the code of your application containing the problem? Thank you very much.

minorpan

**jorma** · 5th May 2006, 17:36

OK minorpan! Here we go - the files mytreewidget.hpp and cpp are below.

Launch the application, and then
- click all tree nodes open
- resize the window from the right-bottom corner so that the first leaf node
(containing the text "aa" just above the long line) is on the right-bottom corner.
The horizontal scroll bar "underlines" this line (so to speak).
- then start resizing the window to the right. You know the long line of aaa's
is just below the horizontal scrollbar.

Do this a couple of times. Experiment with very small changes in the height of the
window. I am sure you will get the flicker-effect and your CPU load rises up, right?

- Jorma

Qt Code:

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// the file mytreewidget.hpp:
#include <QHeaderView>
#include <QTreeWidget>
#include <QApplication>
 
class MyTreeWidget: public QTreeWidget
{
   Q_OBJECT
 
    public:
    MyTreeWidget(QWidget* parent = 0);
    QIcon nodeIcon;  
    QIcon leafIcon;
 
    virtual void resizeEvent( QResizeEvent* event);
 
    protected slots:
    void updateColumnWidth();
 
};

// the file mytreewidget.hpp:
#include <QHeaderView>
#include <QTreeWidget>
#include <QApplication>

class MyTreeWidget: public QTreeWidget
{
   Q_OBJECT

    public:
    MyTreeWidget(QWidget* parent = 0);
    QIcon nodeIcon;  
    QIcon leafIcon;

    virtual void resizeEvent( QResizeEvent* event);

    protected slots:
    void updateColumnWidth();

};

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Qt Code:

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// the file mytreewidget.cpp:
#include "mytreewidget.hpp"
 
MyTreeWidget::MyTreeWidget(QWidget* parent): QTreeWidget(parent)
    {
    // setSelectionMode( QAbstractItemView::SingleSelection);
    setDragEnabled(true); // inherited from QAbstractItemView
    setAcceptDrops(true);
    setDropIndicatorShown(true);
 
 
        setObjectName(QString::fromUtf8("objectView"));
        //setGeometry(QRect(10, 20, 120, 150));
        setColumnCount(2);
        header()->resizeSection(0, 0);
        setItemHidden(headerItem(), true);
 
        QObject::connect(this, SIGNAL(itemChanged(QTreeWidgetItem*, int)), this, SLOT(updateColumnWidth()));
        QObject::connect(this, SIGNAL(itemExpanded(QTreeWidgetItem*)), this, SLOT(updateColumnWidth()));
        QObject::connect(this, SIGNAL(itemCollapsed(QTreeWidgetItem*)), this, SLOT(updateColumnWidth()));
   nodeIcon.addPixmap(style()->standardPixmap(QStyle::SP_DirClosedIcon),
                         QIcon::Normal, QIcon::Off);
    nodeIcon.addPixmap(style()->standardPixmap(QStyle::SP_DirOpenIcon),
                         QIcon::Normal, QIcon::On);
    leafIcon.addPixmap(style()->standardPixmap(QStyle::SP_FileIcon));
    }
 
 
void MyTreeWidget::updateColumnWidth()
{
 
    header()->resizeSection(0, 0);
    resizeColumnToContents(0);
 
}
 
void MyTreeWidget::resizeEvent( QResizeEvent* event)
{
    QTreeWidget::resizeEvent( event);
 
    // in addition to plain old resizing update the column widths:
    updateColumnWidth(); // minorpan's function
};

// the file mytreewidget.cpp:
#include "mytreewidget.hpp"

MyTreeWidget::MyTreeWidget(QWidget* parent): QTreeWidget(parent)
    {
    // setSelectionMode( QAbstractItemView::SingleSelection);
    setDragEnabled(true); // inherited from QAbstractItemView
    setAcceptDrops(true);
    setDropIndicatorShown(true);


        setObjectName(QString::fromUtf8("objectView"));
        //setGeometry(QRect(10, 20, 120, 150));
        setColumnCount(2);
        header()->resizeSection(0, 0);
        setItemHidden(headerItem(), true);

        QObject::connect(this, SIGNAL(itemChanged(QTreeWidgetItem*, int)), this, SLOT(updateColumnWidth()));
        QObject::connect(this, SIGNAL(itemExpanded(QTreeWidgetItem*)), this, SLOT(updateColumnWidth()));
        QObject::connect(this, SIGNAL(itemCollapsed(QTreeWidgetItem*)), this, SLOT(updateColumnWidth()));
   nodeIcon.addPixmap(style()->standardPixmap(QStyle::SP_DirClosedIcon),
                         QIcon::Normal, QIcon::Off);
    nodeIcon.addPixmap(style()->standardPixmap(QStyle::SP_DirOpenIcon),
                         QIcon::Normal, QIcon::On);
    leafIcon.addPixmap(style()->standardPixmap(QStyle::SP_FileIcon));
    }


void MyTreeWidget::updateColumnWidth()
{

    header()->resizeSection(0, 0);
    resizeColumnToContents(0);

}

void MyTreeWidget::resizeEvent( QResizeEvent* event)
{
    QTreeWidget::resizeEvent( event);

    // in addition to plain old resizing update the column widths:
    updateColumnWidth(); // minorpan's function
};

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Qt Code:

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int main(int argc, char* argv[])
{
    QApplication app(argc, argv);
    MyTreeWidget widget;
    QTreeWidgetItem* pItem;
 
    pItem = new QTreeWidgetItem(&widget, QStringList("a"));
    Qt::ItemFlags flags = pItem->flags() & (~ Qt::ItemIsEditable)| Qt::ItemIsSelectable
        | Qt::ItemIsDropEnabled | Qt::ItemIsDragEnabled | Qt::ItemIsEnabled | Qt::ItemIsUserCheckable;
    pItem->setFlags(flags);   
    pItem->setIcon(0, widget.nodeIcon);    
    pItem = new QTreeWidgetItem(pItem, QStringList("aa"));
    pItem->setFlags(flags);pItem->setIcon(0, widget.nodeIcon);    
 
    pItem = new QTreeWidgetItem(pItem, QStringList("aa"));
    pItem->setFlags(flags);pItem->setIcon(0, widget.nodeIcon);    
 
    pItem = new QTreeWidgetItem(pItem, QStringList("aa"));
    pItem->setFlags(flags);pItem->setIcon(0, widget.nodeIcon);    
 
    pItem = new QTreeWidgetItem(pItem, QStringList("aa"));
    pItem->setFlags(flags);pItem->setIcon(0, widget.nodeIcon);    
 
    pItem = new QTreeWidgetItem(pItem, QStringList("aa"));
    pItem->setFlags(flags);pItem->setIcon(0, widget.nodeIcon);    
 
    pItem = new QTreeWidgetItem(pItem, QStringList("aa"));
    pItem->setFlags(flags);pItem->setIcon(0, widget.leafIcon);    
 
    pItem = new QTreeWidgetItem(&widget, QStringList("aaaaaaaaaaaaaaaaaaaaaaaaaaaaa"));
    pItem->setFlags(flags);pItem->setIcon(0, widget.nodeIcon);    
 
    pItem = new QTreeWidgetItem(pItem, QStringList("aa"));
    pItem->setFlags(flags);pItem->setIcon(0, widget.nodeIcon);    
 
    pItem = new QTreeWidgetItem(pItem, QStringList("aa"));
    pItem->setFlags(flags);pItem->setIcon(0, widget.nodeIcon);    
 
 
    widget.show();
    return app.exec();
}

int main(int argc, char* argv[])
{
    QApplication app(argc, argv);
    MyTreeWidget widget;
    QTreeWidgetItem* pItem;

    pItem = new QTreeWidgetItem(&widget, QStringList("a"));
    Qt::ItemFlags flags = pItem->flags() & (~ Qt::ItemIsEditable)| Qt::ItemIsSelectable
        | Qt::ItemIsDropEnabled | Qt::ItemIsDragEnabled | Qt::ItemIsEnabled | Qt::ItemIsUserCheckable;
    pItem->setFlags(flags);   
    pItem->setIcon(0, widget.nodeIcon);    
    pItem = new QTreeWidgetItem(pItem, QStringList("aa"));
    pItem->setFlags(flags);pItem->setIcon(0, widget.nodeIcon);    

    pItem = new QTreeWidgetItem(pItem, QStringList("aa"));
    pItem->setFlags(flags);pItem->setIcon(0, widget.nodeIcon);    

    pItem = new QTreeWidgetItem(pItem, QStringList("aa"));
    pItem->setFlags(flags);pItem->setIcon(0, widget.nodeIcon);    

    pItem = new QTreeWidgetItem(pItem, QStringList("aa"));
    pItem->setFlags(flags);pItem->setIcon(0, widget.nodeIcon);    

    pItem = new QTreeWidgetItem(pItem, QStringList("aa"));
    pItem->setFlags(flags);pItem->setIcon(0, widget.nodeIcon);    

    pItem = new QTreeWidgetItem(pItem, QStringList("aa"));
    pItem->setFlags(flags);pItem->setIcon(0, widget.leafIcon);    

    pItem = new QTreeWidgetItem(&widget, QStringList("aaaaaaaaaaaaaaaaaaaaaaaaaaaaa"));
    pItem->setFlags(flags);pItem->setIcon(0, widget.nodeIcon);    

    pItem = new QTreeWidgetItem(pItem, QStringList("aa"));
    pItem->setFlags(flags);pItem->setIcon(0, widget.nodeIcon);    

    pItem = new QTreeWidgetItem(pItem, QStringList("aa"));
    pItem->setFlags(flags);pItem->setIcon(0, widget.nodeIcon);    


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

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**minorpan** · 5th May 2006, 21:51

Thank you.
I have got the flicker-effect when running your demo application.
I think it's important to resize the viewport when the contents displaying are resized, such as font sizes, right? Therefore the minorpan's function

may still be called within these event handlers. I will try to make it better, thanks for your advice which is really excellent ^_^

minorpan

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