How to make item view render rich (html) text in Qt

Qt Rendering Richtext Qtreeview Qlistview

Qt Problem Overview

Suppose my model has items with the following string for Qt::DisplayRole

<span>blah-blah <b>some text</b> other blah</span>

I want QTreeView (actually, any item view) to render it like a rich text. Instead, item views render it like a pure text by default. How to achieve the desired rendering?

Actually, this is a search results model. User enters a text, some document is searched against that text and the user is presented with search results, where the words being searched should be bolder than surrounding text.

Qt Solutions

Solution 1 - Qt

I guess you can use setItemDelegate method of the treeview to setup custom painter for your treeview items. In the delegate's paint method you can use QTextDocument to load item's text as html and render it. Please check if an example below would work for you:

treeview initialization:

...
    // create simple model for a tree view
    QStandardItemModel *model = new QStandardItemModel();
    QModelIndex parentItem;
    for (int i = 0; i < 4; ++i)
    {
        parentItem = model->index(0, 0, parentItem);
        model->insertRows(0, 1, parentItem);
        model->insertColumns(0, 1, parentItem);
        QModelIndex index = model->index(0, 0, parentItem);
        model->setData(index, "<span>blah-blah <b>some text</b> other blah</span>");
    }
    // create custom delegate
    HTMLDelegate* delegate = new HTMLDelegate();
    // set model and delegate to the treeview object
    ui->treeView->setModel(model);
    ui->treeView->setItemDelegate(delegate);
...

custom delegate implementation

class HTMLDelegate : public QStyledItemDelegate
{
protected:
    void paint ( QPainter * painter, const QStyleOptionViewItem & option, const QModelIndex & index ) const;
    QSize sizeHint ( const QStyleOptionViewItem & option, const QModelIndex & index ) const;
};

void HTMLDelegate::paint(QPainter* painter, const QStyleOptionViewItem & option, const QModelIndex &index) const
{
    QStyleOptionViewItemV4 options = option;
    initStyleOption(&options, index);

    painter->save();

    QTextDocument doc;
    doc.setHtml(options.text);

    options.text = "";
    options.widget->style()->drawControl(QStyle::CE_ItemViewItem, &options, painter);

    painter->translate(options.rect.left(), options.rect.top());
    QRect clip(0, 0, options.rect.width(), options.rect.height());
    doc.drawContents(painter, clip);

    painter->restore();
}

QSize HTMLDelegate::sizeHint ( const QStyleOptionViewItem & option, const QModelIndex & index ) const
{
    QStyleOptionViewItemV4 options = option;
    initStyleOption(&options, index);

    QTextDocument doc;
    doc.setHtml(options.text);
    doc.setTextWidth(options.rect.width());
    return QSize(doc.idealWidth(), doc.size().height());
}

hope this helps, regards

update0: changes to HTMLDelegate to make icons visible and different pen color for selected items

void HTMLDelegate::paint(QPainter* painter, const QStyleOptionViewItem & option, const QModelIndex &index) const
{
    QStyleOptionViewItemV4 options = option;
    initStyleOption(&options, index);

    painter->save();

    QTextDocument doc;
    doc.setHtml(options.text);

    options.text = "";
    options.widget->style()->drawControl(QStyle::CE_ItemViewItem, &options, painter);

    // shift text right to make icon visible
    QSize iconSize = options.icon.actualSize(options.rect.size());
    painter->translate(options.rect.left()+iconSize.width(), options.rect.top());
    QRect clip(0, 0, options.rect.width()+iconSize.width(), options.rect.height());

    //doc.drawContents(painter, clip);

    painter->setClipRect(clip);
    QAbstractTextDocumentLayout::PaintContext ctx;
    // set text color to red for selected item
    if (option.state & QStyle::State_Selected)
        ctx.palette.setColor(QPalette::Text, QColor("red"));
    ctx.clip = clip;
    doc.documentLayout()->draw(painter, ctx);

    painter->restore();
}

Solution 2 - Qt

My answer is mostly inspired by @serge_gubenko's one. However, there were made several improvements so that the code is finally useful in my application.

class HtmlDelegate : public QStyledItemDelegate
{
protected:
    void paint ( QPainter * painter, const QStyleOptionViewItem & option, const QModelIndex & index ) const;
    QSize sizeHint ( const QStyleOptionViewItem & option, const QModelIndex & index ) const;
};

void HtmlDelegate::paint(QPainter *painter, const QStyleOptionViewItem &option, const QModelIndex &index) const
{
    QStyleOptionViewItemV4 optionV4 = option;
    initStyleOption(&optionV4, index);

    QStyle *style = optionV4.widget? optionV4.widget->style() : QApplication::style();

    QTextDocument doc;
    doc.setHtml(optionV4.text);

    /// Painting item without text
    optionV4.text = QString();
    style->drawControl(QStyle::CE_ItemViewItem, &optionV4, painter);

    QAbstractTextDocumentLayout::PaintContext ctx;

    // Highlighting text if item is selected
    if (optionV4.state & QStyle::State_Selected)
        ctx.palette.setColor(QPalette::Text, optionV4.palette.color(QPalette::Active, QPalette::HighlightedText));

    QRect textRect = style->subElementRect(QStyle::SE_ItemViewItemText, &optionV4);
    painter->save();
    painter->translate(textRect.topLeft());
    painter->setClipRect(textRect.translated(-textRect.topLeft()));
    doc.documentLayout()->draw(painter, ctx);
    painter->restore();
}

QSize HtmlDelegate::sizeHint(const QStyleOptionViewItem &option, const QModelIndex &index) const
{
    QStyleOptionViewItemV4 optionV4 = option;
    initStyleOption(&optionV4, index);

    QTextDocument doc;
    doc.setHtml(optionV4.text);
    doc.setTextWidth(optionV4.rect.width());
    return QSize(doc.idealWidth(), doc.size().height());
}

Solution 3 - Qt

Here's the PyQt conversion of the combination of the above answers that worked for me. I would expect this to work virtually identically for PySide as well.

from PyQt4 import QtCore, QtGui

class HTMLDelegate(QtGui.QStyledItemDelegate):
    def paint(self, painter, option, index):
        options = QtGui.QStyleOptionViewItemV4(option)
        self.initStyleOption(options,index)
        
        style = QtGui.QApplication.style() if options.widget is None else options.widget.style()

        doc = QtGui.QTextDocument()
        doc.setHtml(options.text)

        options.text = ""
        style.drawControl(QtGui.QStyle.CE_ItemViewItem, options, painter);

        ctx = QtGui.QAbstractTextDocumentLayout.PaintContext()

        # Highlighting text if item is selected
        #if (optionV4.state & QStyle::State_Selected)
            #ctx.palette.setColor(QPalette::Text, optionV4.palette.color(QPalette::Active, QPalette::HighlightedText));

        textRect = style.subElementRect(QtGui.QStyle.SE_ItemViewItemText, options)
        painter.save()
        painter.translate(textRect.topLeft())
        painter.setClipRect(textRect.translated(-textRect.topLeft()))
        doc.documentLayout().draw(painter, ctx)

        painter.restore()

    def sizeHint(self, option, index):
        options = QtGui.QStyleOptionViewItemV4(option)
        self.initStyleOption(options,index)
        
        doc = QtGui.QTextDocument()
        doc.setHtml(options.text)
        doc.setTextWidth(options.rect.width())
        return QtCore.QSize(doc.idealWidth(), doc.size().height())

Solution 4 - Qt

This one is in PySide. Rather than doing a lot of custom drawing, I pass the QPainter to the QLabel and make it draw itself. Highlighting code borrowed from other answers.

from PySide import QtGui

class TaskDelegate(QtGui.QItemDelegate):
    #https://doc.qt.io/archives/qt-4.7/qitemdelegate.html#drawDisplay
    #https://doc.qt.io/archives/qt-4.7/qwidget.html#render
    def drawDisplay(self, painter, option, rect, text):
        label = QtGui.QLabel(text)

        if option.state & QtGui.QStyle.State_Selected:
            p = option.palette
            p.setColor(QtGui.QPalette.WindowText, p.color(QtGui.QPalette.Active, QtGui.QPalette.HighlightedText))
            
            label.setPalette(p)

        label.render(painter, rect.topLeft(), renderFlags=QtGui.QWidget.DrawChildren)

Solution 5 - Qt

Writing up yet another answer for how this can be done in C++. The difference to the answers provided so far is that this is for Qt5 and not Qt4. Most importantly however the previous answers neglected that the item delegate should be able to align the text as specified (e.g. in a QTreeWidget). Additionally I also implemented a way to elide rich text in order to get a consistent feeling with plaintext delegates (in ItemViews).

So without further ado, here is my code for a RichTextDelegate:

void RichTextItemDelegate::paint(QPainter *painter, const QStyleOptionViewItem &inOption,
								 const QModelIndex &index) const {
	QStyleOptionViewItem option = inOption;
	initStyleOption(&option, index);

	if (option.text.isEmpty()) {
		// This is nothing this function is supposed to handle
		QStyledItemDelegate::paint(painter, inOption, index);

		return;
	}

	QStyle *style = option.widget ? option.widget->style() : QApplication::style();

	QTextOption textOption;
	textOption.setWrapMode(option.features & QStyleOptionViewItem::WrapText ? QTextOption::WordWrap
																			: QTextOption::ManualWrap);
	textOption.setTextDirection(option.direction);

	QTextDocument doc;
	doc.setDefaultTextOption(textOption);
	doc.setHtml(option.text);
	doc.setDefaultFont(option.font);
	doc.setDocumentMargin(0);
	doc.setTextWidth(option.rect.width());
	doc.adjustSize();

	if (doc.size().width() > option.rect.width()) {
		// Elide text
		QTextCursor cursor(&doc);
		cursor.movePosition(QTextCursor::End);

		const QString elidedPostfix = "...";
		QFontMetrics metric(option.font);
#if QT_VERSION >= QT_VERSION_CHECK(5, 11, 0)
		int postfixWidth = metric.horizontalAdvance(elidedPostfix);
#else
		int postfixWidth = metric.width(elidedPostfix);
#endif
		while (doc.size().width() > option.rect.width() - postfixWidth) {
			cursor.deletePreviousChar();
			doc.adjustSize();
		}

		cursor.insertText(elidedPostfix);
	}

	// Painting item without text (this takes care of painting e.g. the highlighted for selected
	// or hovered over items in an ItemView)
	option.text = QString();
	style->drawControl(QStyle::CE_ItemViewItem, &option, painter, inOption.widget);

	// Figure out where to render the text in order to follow the requested alignment
	QRect textRect = style->subElementRect(QStyle::SE_ItemViewItemText, &option);
	QSize documentSize(doc.size().width(), doc.size().height()); // Convert QSizeF to QSize
	QRect layoutRect = QStyle::alignedRect(Qt::LayoutDirectionAuto, option.displayAlignment, documentSize, textRect);

	painter->save();

	// Translate the painter to the origin of the layout rectangle in order for the text to be
	// rendered at the correct position
	painter->translate(layoutRect.topLeft());
	doc.drawContents(painter, textRect.translated(-textRect.topLeft()));

	painter->restore();
}

QSize RichTextItemDelegate::sizeHint(const QStyleOptionViewItem &inOption, const QModelIndex &index) const {
	QStyleOptionViewItem option = inOption;
	initStyleOption(&option, index);

	if (option.text.isEmpty()) {
		// This is nothing this function is supposed to handle
		return QStyledItemDelegate::sizeHint(inOption, index);
	}

	QTextDocument doc;
	doc.setHtml(option.text);
	doc.setTextWidth(option.rect.width());
	doc.setDefaultFont(option.font);
	doc.setDocumentMargin(0);

	return QSize(doc.idealWidth(), doc.size().height());
}

Solution 6 - Qt

Just a slight update from jbmohler's answer, for PyQt5: some classes have apparently been shifted to QtWidgets.

This is way beyond my paygrade (i.e. knowledge of the nuts and bolts behind PyQt5).

I echo the sentiment expressed in Cecil Curry's comment to the question. It is now 2021, and we appear still to have to struggle with this sort of hack. Ridiculous. I've been impressed by Qt5 to date, as compared to JavaFX for example. This deficiency is a let-down.

    class HTMLDelegate( QtWidgets.QStyledItemDelegate ):
        def __init__( self ):
            super().__init__()
            # probably better not to create new QTextDocuments every ms
            self.doc = QtGui.QTextDocument()
    
        def paint(self, painter, option, index):
            options = QtWidgets.QStyleOptionViewItem(option)
            self.initStyleOption(options, index)
            painter.save()
            self.doc.setTextWidth(options.rect.width())                
            self.doc.setHtml(options.text)
            self.doc.setDefaultFont(options.font)
            options.text = ''
            options.widget.style().drawControl(QtWidgets.QStyle.CE_ItemViewItem, options, painter)
            painter.translate(options.rect.left(), options.rect.top())
            clip = QtCore.QRectF(0, 0, options.rect.width(), options.rect.height())
            painter.setClipRect(clip)
            ctx = QtGui.QAbstractTextDocumentLayout.PaintContext()
            ctx.clip = clip
            self.doc.documentLayout().draw(painter, ctx)
            painter.restore()
    
        def sizeHint( self, option, index ):
            options = QtWidgets.QStyleOptionViewItem(option)
            self.initStyleOption(option, index)
            self.doc.setHtml(option.text)
            self.doc.setTextWidth(option.rect.width())
            return QtCore.QSize(self.doc.idealWidth(), self.doc.size().height())

Content Type	Original Author	Original Content on Stackoverflow
Question	Anthony Serdyukov	View Question on Stackoverflow
Solution 1 - Qt	serge_gubenko	View Answer on Stackoverflow
Solution 2 - Qt	Anthony Serdyukov	View Answer on Stackoverflow
Solution 3 - Qt	jbmohler	View Answer on Stackoverflow
Solution 4 - Qt	Pepijn	View Answer on Stackoverflow
Solution 5 - Qt	Raven	View Answer on Stackoverflow
Solution 6 - Qt	mike rodent	View Answer on Stackoverflow