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Thread: QTableWidget NW corner header item?

  1. #1
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    Question QTableWidget NW corner header item?

    Embarassing to ask, but how would I access the top left corner header item in a QTableWidget that has both a horizontal and a vertical header? This is the header item they have in common. I can use

    Qt Code:
    1. QTableWidget::setHorizontalHeaderLabels ( const QStringList & labels )
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    and
    Qt Code:
    1. QTableWidget::setVerticalHeaderLabels ( const QStringList & labels )
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    but they don't seem to provide access to the item at the corner. Nor do

    Qt Code:
    1. QTableWidgetItem * QTableWidget::horizontalHeaderItem ( int column ) const
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    and
    Qt Code:
    1. QTableWidgetItem * QTableWidget::verticalHeaderItem ( int row) const
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    Perhaps accessing a header itself via

    Qt Code:
    1. QHeaderView * QTableView::horizontalHeader () const
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    or
    Qt Code:
    1. QHeaderView * QTableView::verticalHeader () const
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    but then what to do with it?

    thanks!

  2. #2
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    Default Re: QTableWidget NW corner header item?

    What would you like to do with it? It's not a header item actually but a button (for more information, see QTableCornerButton at the beginning of src/gui/itemviews/qtableview.cpp).
    J-P Nurmi

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    Default Re: QTableWidget NW corner header item?

    I'd like to set its text; that's all.

    I see the code you pointed me to -- thanks. QTableView's private cornerWidget member is the QTableCornerButton, and it oddly hides another member of the same name down the inheritance chain, namely QAbstractScrollArea::cornerWidget. Only the latter is exposed via the method cornerWidget(). Doh. QTableWidget::cornerWidget() returns not the QTableCornerButton instance, but QAbstractScrollArea::cornerWidget, which is understandably NULL. Wish there was a QTableView::cornerButton() method.

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    Default Re: QTableWidget NW corner header item?

    It's still possible with some rather ugly "hacking". One would need to use for example QObject::findChild() to get access to the private corner button. An event filter is required for "overriding" the button's paintEvent() (QTableCornerButton::paintEvent() doesn't paint the text even if the button had text set). I have attached an example.

    This is, of course, not recommended way for doing it. It is a private button and may be a subject to change in the future. I suggest sending a suggestion about the issue to the Task-Tracker.
    Attached Files Attached Files
    J-P Nurmi

  5. The following 2 users say thank you to jpn for this useful post:

    McKee (30th March 2007), ykozlov (12th November 2012)

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    Default Re: QTableWidget NW corner header item?

    Wow! Nice work. Thanks for the example code.

    Another way to solve the problem is to just create a new leftmost column, for which I can set the text of the top header item. I was hoping to avoid that because my table works better with my leftmost data in the vertical header items. But it's do-able.

    I'll look into the TaskTracker suggestion.

    McKee

  7. #6
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    Default Re: QTableWidget NW corner header item?

    Does anyone know if there is there any way to format the NW corner button using a stylesheet? Setting the following style sheet on the NW corner button in my CTableWidget constructor doesn't seem to do anything:

    Qt Code:
    1. CTableWidget::CTableWidget( QWidget* parent ):
    2. QTableWidget( parent )
    3. {
    4. QList< QAbstractButton* > buttons = qFindChildren< QAbstractButton* >( this );
    5. for ( int i=0; i<buttons.size(); ++i )
    6. {
    7. buttons[i]->setStyleSheet( "QWidget{ background-color:red; }" );
    8. }
    9. }
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    I can paint the button myself using an event filter, but it doesn't seem like an end user can modify the appearance.

    TIA,

    jt

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    Default Re: QTableWidget NW corner header item?

    Hi,

    post code from jtaylor108 seems to work for set backgroud color. Anyway I try to change a text of top left corner but it's not changed.
    I use same code but instead setStyleSheet I used setText() but text was not set. I s there any other option how to do this? Thanks

  9. #8
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    Default Re: QTableWidget NW corner header item?

    This thread has been *very* useful, so I will add some points.

    First, you can indeed use a setStyleSheet call in your table widget class to change the corner button border and background as follows:

    Qt Code:
    1. setStyleSheet("QTableCornerButton::section {border: 2px outset red; background: green;}");
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    I did not need this functionality for what I wanted to do, but it is still a useful trick to know.

    What I wanted to do was place an icon in the corner button to indicate that there is indeed a functional button at that location (many of my users did not know that clicking the corner will select all of the table cells). The 29th March 2007 posted by jpn was *extremely* helpful with a slight change. In jpn's example, he sets the button text in the TableWidget constructor like this:

    Qt Code:
    1. btn->setText("Text");
    2. opt.text = btn->text();
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    I set the button icon instead of the text:

    Qt Code:
    1. QIcon myIcon = getMyIcon(); // this function returns a QIcon
    2. btn->setIcon(myIcon);
    3. opt.icon = btn->icon();
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    The "opt.text = btn->text();" line in the eventFilter function also has to be changed to "opt.icon = btn->icon();"

    I also changed the functionality of the corner button. Instead of simply selecting all of the cells, I altered the corner button to toggle between selecting all the cells and clearing the selection.

    Here is the relevant code from my QTableWidget constructor:

    Qt Code:
    1. // Take the click signal off of the corner widget and replace it with our own
    2. // This enables toggling the selection when the corner button is clicked.
    3. // This is more ergonomic than the default behavior of only selecting all of the cells.
    4. m_toggleCornerSelection = false;
    5. QAbstractButton *btn = findChild<QAbstractButton *>();
    6. if (btn != NULL) {
    7. btn->disconnect(SIGNAL(clicked()));
    8. connect(btn, SIGNAL(clicked()), this, SLOT(handleCornerButtonClicked()));
    9. MyIcons *iconList = MyIcons::getIcons(); // our class that handles all of our icons
    10. QIcon selectIcon = iconList->getIconSet(MyIcons::SELECT_ALL);
    11. btn->setIcon(selectIcon);
    12. // btn->setText("text");
    13. btn->setToolTip("Toggle selecting all table cells");
    14. btn->installEventFilter(this);
    15.  
    16. // adjust the width of the vertical header to match the preferred corner button width
    17. // (unfortunately QAbstractButton doesn't implement any size hinting functionality)
    18. // opt.text = btn->text();
    19. opt.icon = btn->icon();
    20. QSize s = (btn->style()->sizeFromContents(QStyle::CT_HeaderSection, &opt, QSize(), btn).
    21. expandedTo(QApplication::globalStrut()));
    22. if (s.isValid()) {
    23. verticalHeader()->setMinimumWidth(s.width());
    24. }
    25. }
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    I then implemented the following code:

    Qt Code:
    1. //-----------------------------------------------------------------------------
    2. // Event filter used to draw an icon in the top-left corner of the table widget
    3. //-----------------------------------------------------------------------------
    4.  
    5. bool MySpreadsheet::eventFilter(QObject* o, QEvent* e)
    6. {
    7. if (e->type() == QEvent::Paint) {
    8. QAbstractButton* btn = qobject_cast<QAbstractButton*>(o);
    9. if (btn) {
    10. // paint by hand (borrowed from QTableCornerButton)
    11. opt.init(btn);
    12. QStyle::State styleState = QStyle::State_None;
    13. if (btn->isEnabled())
    14. styleState |= QStyle::State_Enabled;
    15. if (btn->isActiveWindow())
    16. styleState |= QStyle::State_Active;
    17. if (btn->isDown())
    18. styleState |= QStyle::State_Sunken;
    19. opt.state = styleState;
    20. opt.rect = btn->rect();
    21. // opt.text = btn->text(); // this line is the only difference to QTableCornerButton
    22. opt.icon = btn->icon(); // this line is the only difference to QTableCornerButton
    23. opt.position = QStyleOptionHeader::OnlyOneSection;
    24. QStylePainter painter(btn);
    25. painter.drawControl(QStyle::CE_Header, opt);
    26. return true; // eat event
    27. }
    28. }
    29. return false;
    30. }
    31.  
    32. ...
    33. //-----------------------------------------------------------------------------
    34. // Handle clicking the upper-left corner button. This action toggles the selection of all of the cells
    35. // off and on.
    36. //-----------------------------------------------------------------------------
    37.  
    38. void MySpreadsheet::handleCornerButtonClicked()
    39. {
    40. if (m_toggleCornerSelection) {
    41. clearSelection();
    42. } else {
    43. selectAll();
    44. }
    45. m_toggleCornerSelection = !m_toggleCornerSelection;
    46. }
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    I hope that is helpful to those who want similar functionality.

  10. #9
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    Default Re: QTableWidget NW corner header item?

    I am using PyQt and none of the above solutions worked for me. However I was able to successfully hide the button by sub-classing QTableView and overriding the updateGeometries function.

    Qt Code:
    1. class MyTableView(QTableView):
    2.  
    3. def updateGeometries(self):
    4. # Call the updateGeometries function defined by QTableView first
    5. super(MyTableView, self).updateGeometries()
    6. # Find the corner widget and hide it!
    7. self.findChild(QAbstractButton).setHidden(True)
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  11. #10
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    Default Re: QTableWidget NW corner header item?

    I am trying to do something similar by changing the button icon. But I am using an icon the is not square. It is twice as wide as it is high. The icon is displayed but is not taking up the whole area of the button (I have set the header width to be twice as wide as it is high). To overcome this I am using:

    Qt Code:
    1. btn->setIconSize(m_iconSize);
    2. QPixmap pixmap = btn->icon().pixmap(m_iconSize, QIcon::Normal, QIcon::On);
    3. QStylePainter painter(btn);
    4. painter.drawItemPixmap(btn->rect(), Qt::AlignCenter, pixmap);
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    Instead of

    Qt Code:
    1. btn->setIconSize(m_iconSize);
    2. QStylePainter painter(btn);
    3. painter.drawControl(QStyle::CE_Header, opt);
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    So that the icon pixmap is being directly drawn to the area where the control is. This works but not as well as I would like. Is there any way to force painter.drawControl() to draw the icon full size?

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