Hyperlinks in QTreeView without QLabel

I'm trying to display clickable hyperlinks in my QTreeView.

I was able to do this using QLabels and QTreeView.setIndexWidget per the recommendations from this question.

Unfortunately, my QTreeView can be rather large (1000s of items), and creating 1000s of QLabels is slow.

The upside is that I can use a Delegate in my QTreeView to draw text that looks like hyperlinks. This is super fast.

The problem now is that I need them to respond like hyperlinks (i.e. mouseover hand cursor, respond to clicks, etc.), but I'm not sure what the best way to go about that is.

I've been able to sort of fake it by just connecting to the clicked() signal of the QTreeView, but it's not exactly the same, because it responds to the whole cell, and not just the text inside the cell.

Solution

The easiest way to do that seems to be by subclassing QItemDelegate, because the text is drawn by a separate virtual function, drawDisplay (with QStyledItemDelegate you would almost have to redraw the item from scratch and you would need an additional class deriving from QProxyStyle):

the HTML text is drawn with QTextDocument and QTextDocument.documentLayout().draw(),
when the mouse enters an item, that same item is repainted and drawDisplay is called, we save the position were we are drawing the text (so the saved position is always the position of the text for the item over which the mouse is),
that position is used in editorEvent to get the relative position of the mouse inside the document and to get the link at that position in the document with QAbstractTextDocumentLayout.anchorAt.

import sys
from PySide.QtCore import *
from PySide.QtGui import *

class LinkItemDelegate(QItemDelegate):
    linkActivated = Signal(str)
    linkHovered = Signal(str)  # to connect to a QStatusBar.showMessage slot

    def __init__(self, parentView):
        QItemDelegate.__init__(self, parentView)
        assert isinstance(parentView, QAbstractItemView), \
            "The first argument must be the view"

        # We need that to receive mouse move events in editorEvent
        parentView.setMouseTracking(True)

        # Revert the mouse cursor when the mouse isn't over 
        # an item but still on the view widget
        parentView.viewportEntered.connect(parentView.unsetCursor)

        # documents[0] will contain the document for the last hovered item
        # documents[1] will be used to draw ordinary (not hovered) items
        self.documents = []
        for i in range(2):
            self.documents.append(QTextDocument(self))
            self.documents[i].setDocumentMargin(0)
        self.lastTextPos = QPoint(0,0)

    def drawDisplay(self, painter, option, rect, text): 
        # Because the state tells only if the mouse is over the row
        # we have to check if it is over the item too
        mouseOver = option.state & QStyle.State_MouseOver \
            and rect.contains(self.parent().viewport() \
                .mapFromGlobal(QCursor.pos())) \
            and option.state & QStyle.State_Enabled

        if mouseOver:
            # Use documents[0] and save the text position for editorEvent
            doc = self.documents[0]                
            self.lastTextPos = rect.topLeft()
            doc.setDefaultStyleSheet("")
        else:
            doc = self.documents[1]
            # Links are decorated by default, so disable it
            # when the mouse is not over the item
            doc.setDefaultStyleSheet("a {text-decoration: none}")

        doc.setDefaultFont(option.font)
        doc.setHtml(text)

        painter.save()
        painter.translate(rect.topLeft())
        ctx = QAbstractTextDocumentLayout.PaintContext()
        ctx.palette = option.palette
        doc.documentLayout().draw(painter, ctx)
        painter.restore()

    def editorEvent(self, event, model, option, index):
        if event.type() not in [QEvent.MouseMove, QEvent.MouseButtonRelease] \
            or not (option.state & QStyle.State_Enabled):
            return False                        
        # Get the link at the mouse position
        # (the explicit QPointF conversion is only needed for PyQt)
        pos = QPointF(event.pos() - self.lastTextPos)
        anchor = self.documents[0].documentLayout().anchorAt(pos)
        if anchor == "":
            self.parent().unsetCursor()
        else:
            self.parent().setCursor(Qt.PointingHandCursor)               
            if event.type() == QEvent.MouseButtonRelease:
                self.linkActivated.emit(anchor)
                return True 
            else:
                self.linkHovered.emit(anchor)
        return False

    def sizeHint(self, option, index):
        # The original size is calculated from the string with the html tags
        # so we need to subtract from it the difference between the width
        # of the text with and without the html tags
        size = QItemDelegate.sizeHint(self, option, index)

        # Use a QTextDocument to strip the tags
        doc = self.documents[1]
        html = index.data() # must add .toString() for PyQt "API 1"
        doc.setHtml(html)        
        plainText = doc.toPlainText()

        fontMetrics = QFontMetrics(option.font)                
        diff = fontMetrics.width(html) - fontMetrics.width(plainText)

        return size - QSize(diff, 0)

As long as you don't enable the automatic column resizing to contents (which would call sizeHint for every items), it doesn't seem to be slower than without the delegate.
With a custom model, it might be possible to speed it up by caching directly some data inside the model (for example, by using and storing QStaticText for non hovered items instead of QTextDocument).