use delegate to draw a line under currently pointed row item while dragging

simple_treeWidget_delegate.py

#!/usr/bin/env python2
import os
import sys
import re

from PyQt4 import QtGui, QtCore
from PyQt4.QtCore import Qt, QString


class MyDelegate(QtGui.QStyledItemDelegate):

    def paint(self, painter, option, index):
        QtGui.QStyledItemDelegate.paint(self, painter, option, index)
        painter.save()
        data = index.model().data(index, Qt.UserRole).toInt()
        # if UserRole = 1 draw custom line
        if data[1] and data[0] == 1:
            line = QtCore.QLine(option.rect.topLeft(), option.rect.topRight())
            painter.drawLine(line)
        painter.restore()


class MyTreeWidget(QtGui.QTreeWidget):

    def paintEventx(self, event):
        painter = QtGui.QPainter(self.viewport())
        self.drawTree(painter, event.region())
        # in original implementation, it calls an inline function paintDropIndicator here

    def mouseMoveEvent(self, e):
        mimeData = self.model().mimeData(self.selectedIndexes())
        drag = QtGui.QDrag(self)
        drag.setMimeData(mimeData)
        # pixmap = QtGui.QPixmap('xxx.png')
        # drag.setPixmap(pixmap)
        drag.exec_(QtCore.Qt.MoveAction)

    def dragMoveEvent(self, event):
        pos = event.pos()
        item = self.itemAt(pos)

        # If hovered over an item during drag, set UserRole = 1
        if item:
            index = self.indexFromItem(item)
            self.model().setData(index, 1, Qt.UserRole)

        # reset UserRole to 0 for all other indices
        # This only reset topLevel item UserRole data
        # for i in range(self.model().rowCount()):
        #     _index = self.model().index(i, 0)
        #     if not item or index != _index:
        #         self.model().setData(_index, 0, Qt.UserRole)

        iterator = QtGui.QTreeWidgetItemIterator(self)
        while iterator.value():
            item_iter = iterator.value()
            if item_iter is not item:
                _index = self.indexFromItem(item_iter, 0)
                self.model().setData(_index, 0, Qt.UserRole)
            iterator += 1


class TheUI(QtGui.QDialog):

    def __init__(self, args=None, parent=None):
        super(TheUI, self).__init__(parent)
        self.layout1 = QtGui.QVBoxLayout(self)
        treeWidget = MyTreeWidget()

        # treeWidget.setSelectionMode( QtGui.QAbstractItemView.ExtendedSelection )

        button1 = QtGui.QPushButton('Add')
        button2 = QtGui.QPushButton('Add Child')

        self.layout1.addWidget(treeWidget)

        self.layout2 = QtGui.QHBoxLayout()
        self.layout2.addWidget(button1)
        self.layout2.addWidget(button2)

        self.layout1.addLayout(self.layout2)

        treeWidget.setHeaderHidden(True)

        treeWidget.setItemDelegate(MyDelegate())

        self.treeWidget = treeWidget
        self.button1 = button1
        self.button2 = button2
        self.button1.clicked.connect(lambda *x: self.addCmd())
        self.button2.clicked.connect(lambda *x: self.addChildCmd())

        HEADERS = ("script", "chunksize", "mem")
        self.treeWidget.setHeaderLabels(HEADERS)
        self.treeWidget.setColumnCount(len(HEADERS))

        self.treeWidget.setColumnWidth(0, 160)
        self.treeWidget.header().show()

        self.treeWidget.setDragDropMode(QtGui.QAbstractItemView.InternalMove)

        self.resize(500, 500)
        for i in xrange(6):
            item = self.addCmd(i)
            if i in (3, 4):
                self.addChildCmd()
                if i == 4:
                    self.addCmd('%s-2' % i, parent=item)

        self.treeWidget.expandAll()
        self.setStyleSheet("QTreeWidget::item{ height: 30px;  }")

    def addChildCmd(self):
        parent = self.treeWidget.currentItem()
        self.addCmd(parent=parent)
        self.treeWidget.setCurrentItem(parent)

    def addCmd(self, i=None, parent=None):
        'add a level to tree widget'

        root = self.treeWidget.invisibleRootItem()
        if not parent:
            parent = root

        if i is None:
            if parent == root:
                i = self.treeWidget.topLevelItemCount()
            else:
                i = str(parent.text(0))[7:]
                i = '%s-%s' % (i, parent.childCount() + 1)

        item = QtGui.QTreeWidgetItem(parent, ['script %s' % i, '1', '150'])

        self.treeWidget.setCurrentItem(item)
        self.treeWidget.expandAll()
        return item

if __name__ == '__main__':
    app = QtGui.QApplication(sys.argv)
    gui = TheUI()
    gui.show()
    app.exec_()