custom painting in QListWidget

[Andrew]

Hello,

I am using a QListWidget in ListMode and I want the items to be displayed a little offset'ed (10 pixels in the right and down)

How can I override the default items paint ?

Do I need to create my own model ? Can i override paint event and change the input rectangle ?

thank you.

[jacek]

Do I need to create my own model ?

You can't use a custom model with QListWidget. To do that you will have to switch to QListView.

Can i override paint event and change the input rectangle ?

A custom delegate should be enough. See QItemDelegate.

[Andrew]

I did create my own delegate (a class derived from QItemDelegate and set using setItemDelegate )
and overriden
void paint ( QPainter * painter, const QStyleOptionViewItem & option, const QModelIndex & index ) const

but i dont know how to modify the items position.
can you please be specific ?

[Andrew]

You can modify its copy.

what's the purpose of modifying an object copy if you don;t modify the object itself ?

i begin to lose any confident to find a solution to my problem.
i see some people here reply just for the pleasure of doing that.

[jacek]

what's the purpose of modifying an object copy if you don;t modify the object itself ?

Too pass further the changed object:

void MyDelegate::paint(QPainter *painter, const QStyleOptionViewItem &option, const QModelIndex &index) const
{
   QStyleOptionViewItem newOption( option );
   // change newOption
   QItemDelegate::paint(painter, newOption, index);
}

void MyDelegate::paint(QPainter *painter, const QStyleOptionViewItem &option, const QModelIndex &index) const
{
   QStyleOptionViewItem newOption( option );
   // change newOption
   QItemDelegate::paint(painter, newOption, index);
}

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[Andrew]

thanks.
i simply could not see that.
but now i seem to have another problem.

void MyDelegate::paint ( ..)
{
        QStyleOptionViewItem newOption( option );
        newOption.rect.translate(QPoint(40,40));
 
         QItemDelegate::paint(painter, newOption, index);
}

void MyDelegate::paint ( ..)
{
        QStyleOptionViewItem newOption( option );
        newOption.rect.translate(QPoint(40,40));

         QItemDelegate::paint(painter, newOption, index);
}

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when i select items the widget doesnt display the items correctly.
for example, if i select the 2nd item, the horizontal lower half of the first item is erased but the selected item is displayed ok.
but after i play around with selection the whole thing becomes a bigger mess.

what do you think ?
is delegate an option for modifying ListWidget items position ?
is this possible ?

thanks

[jacek]

when i select items the widget doesnt display the items correctly.

Actually it's almost the same solution as using QPainter::translate(). What you can try to do is to change the decorationSize --- this should move items to the right.

[wysota]

Maybe you could just center the item using regular methods (by setting the alignment role)? Depends how much you want your items shifted...

[jacek]

If you could post a screenshot, we would be able to fully understand why and where do you want to move those items.

[Andrew]

the default item painting in QListWidget is with icon painted very close to the widget left margin.
i want to have an offset.
in the same way, i want a vertical offset from the top.

i am using icon and text in items.

at this moment I see that the solution is to custom paint in a delegate the item (paint the icon and text and my desired locations).

what do you think ?

I have a question. how do I find out the QListWidget client rectangle minus the area occupied by the horizontal scrollbar widget ?
after i add items, I need to determine the width of this area.
i guess QListWidget::contentsRect( ) is the widget client rect but how do I find the scrollbar width ?
i tried with
ui.listWidget->verticalScrollBar()->rect()
after i inserted the items but it doesnt give the real size.
is there any way to find a 'metric' of a scrollbar (like how in win32 api is GetSystemMetrics if i remember right)

[wysota]

You don't have to do any custom painting. Just subclass QItemDelegate and reimplement its drawDisplay and drawDecoration methods calling the base class implementation with a reduced rectangle.

void MyItemDelegate::drawDecoration ( QPainter * painter, const QStyleOptionViewItem & option, const QRect & rect, const QPixmap & pixmap ) const {
  QItemDelegate::drawDecoration(painter, option, rect.adjusted(2,2,0, -2), pixmap);
}

void MyItemDelegate::drawDecoration ( QPainter * painter, const QStyleOptionViewItem & option, const QRect & rect, const QPixmap & pixmap ) const {
  QItemDelegate::drawDecoration(painter, option, rect.adjusted(2,2,0, -2), pixmap);
}

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You can also reimplement sizeHint to make sure the item is bigger than is needed to fit the text and icon.

[Andrew]

I didnt look at QItemDelegate to see what can be overriden.
Thanks alot !

I still need to know the width of the vertical scrollbar.
I'll try to explain why.
I want QListWidget to display only 4 items at once (icons with text underneath)
(so the client rect is splitted in 4 equal parts).

For this i set IconMode view mode.
In order to display only 4 items I need to compute an item size and call QListWidgetItem::setHintSize( )
The item width cannot be just QListWidget::contentsRect().Width( ) / 2 because I need to take into account the left vertical scrollbar width also. Otherwise a horizontal scrollbar will appear.

that's why I need the width of the vertical scrollbar.

After I inserted items I tried to call
QRect rc = ui.listWidget->verticalScrollBar()->rect();
but it does not give consistent results.
I observed that the right size is computed after the first display.
is there a way to get scrollbar metrics \ force internal computation before actual painting ?

[wysota]

int width = style()->pixelMetric(QStyle::PM_ScrollBarExtent);

int width = style()->pixelMetric(QStyle::PM_ScrollBarExtent);

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