QStyledItemDelegate subclass implementation of paint()

Question

I have a QStandardItemModel being displayed in two QTreeViews. The first TreeView uses the standard QStyledItemDelegate without any alterations and shows the items with a checkbox, an icon and their display text. The second view is supposed to show the same tree, although a custom implementation of QStyledItemDelegate is supposed to do the following:

• Show some items' display text in italics
• Show some items' display text in red
• Remove the checkbox for every item
• Make only those items selectable that are not italics

Whether items are in italics/not clickable or not and whether they're displayed in red or not is saved in a custom DataRole and accessed using index.data(custom_role).

My problem is: I can't get text to be shown in red and I have no idea how to remove the checkbox, or how to make items selectable or not.

Here's what I have:

class PostProcessedDelegate(QtWidgets.QStyledItemDelegate):

    def __init__(self):
        super().__init__()

    def paint(self, painter, option, index): 
        custom_option = QtWidgets.QStyleOptionViewItem(option)
        custom_painter = painter

        if not index.data(Item.IS_PROCESSED):
            custom_option.font.setItalic(True)
            #ALSO MAKE ITEM NON-SELECTABLE HERE 
    
        if index.data(Item.HAS_PROCESSING_ERROR):
            custom_painter.setPen(QtGui.QColor(255,0,0)) #THIS DOESNT HAVE ANY EFFECT
            
        #REMOVE CHECKBOX BEFORE PAINTING
        super().paint(custom_painter, custom_option, index) 

This screenshot shows the first TreeView to the left (the one without any alterations) and the second to the right, with only some of the required changes in effect.

Answer 1

It is not necessary to override the paint method but to modify the QStyleOptionViewItem in initStyleOption, for selection you must override the selectionCommand method of the QTreeView:

from enum import IntEnum, auto
import random
import sys

from PyQt5 import QtCore, QtGui, QtWidgets


class Item(IntEnum):
    IS_PROCESSED = QtCore.Qt.UserRole
    HAS_PROCESSING_ERROR = auto()


def create_icon():
    color = QtGui.QColor(*random.sample(range(255), 3))
    pixmap = QtGui.QPixmap(128, 128)
    pixmap.fill(color)
    return QtGui.QIcon(pixmap)


class StyledItemDelegate(QtWidgets.QStyledItemDelegate):
    def initStyleOption(self, option, index):
        super().initStyleOption(option, index)
        if not index.data(Item.IS_PROCESSED):
            option.font.setItalic(True)

        if index.data(Item.HAS_PROCESSING_ERROR):
            option.palette.setBrush(QtGui.QPalette.Text, QtGui.QColor(255, 0, 0))

        option.features &= ~QtWidgets.QStyleOptionViewItem.HasCheckIndicator


class TreeView(QtWidgets.QTreeView):
    def __init__(self, parent=None):
        super().__init__(parent)
        delegate = StyledItemDelegate(self)
        self.setItemDelegate(delegate)

    def selectionCommand(self, index, event):
        if not index.data(Item.IS_PROCESSED):
            return QtCore.QItemSelectionModel.NoUpdate
        return super().selectionCommand(index, event)


class Widget(QtWidgets.QWidget):
    def __init__(self, parent=None):
        super().__init__(parent)

        model = QtGui.QStandardItemModel(self)

        left_view = QtWidgets.QTreeView()
        right_view = TreeView()

        lay = QtWidgets.QHBoxLayout(self)
        lay.addWidget(left_view)
        lay.addWidget(right_view)

        left_view.setModel(model)
        right_view.setModel(model)

        root_item = QtGui.QStandardItem("Root")
        model.appendRow(root_item)

        self.populate(root_item, 3)
        left_view.expandAll()
        right_view.expandAll()

    def populate(self, root_item, level):
        for i in range(random.randint(2, 4)):
            it = QtGui.QStandardItem("item {}".format(i))
            it.setIcon(create_icon())
            it.setCheckable(True)
            it.setData(random.choice([True, False]), Item.IS_PROCESSED)
            it.setData(random.choice([True, False]), Item.HAS_PROCESSING_ERROR)
            root_item.appendRow(it)
            next_level = level - 1
            if next_level > 0:
                self.populate(it, next_level)


if __name__ == "__main__":
    app = QtWidgets.QApplication(sys.argv)

    w = Widget()
    w.show()

    sys.exit(app.exec_())