PyQt5 TreeView with QAbstractItemModel

treeview_test.py

"""
Reworked code based on
http://trevorius.com/scrapbook/uncategorized/pyqt-custom-abstractitemmodel/

Adapted to Qt5 and fixed column/row bug.

TODO: handle changing data.
"""

import sys
from PyQt5 import QtCore, QtWidgets


class CustomNode(object):
    def __init__(self, data):
        self._data = data
        if type(data) == tuple:
            self._data = list(data)
        if type(data) is str or not hasattr(data, '__getitem__'):
            self._data = [data]

        self._columncount = len(self._data)
        self._children = []
        self._parent = None
        self._row = 0

    def data(self, column):
        if column >= 0 and column < len(self._data):
            return self._data[column]

    def columnCount(self):
        return self._columncount

    def childCount(self):
        return len(self._children)

    def child(self, row):
        if row >= 0 and row < self.childCount():
            return self._children[row]

    def parent(self):
        return self._parent

    def row(self):
        return self._row

    def addChild(self, child):
        child._parent = self
        child._row = len(self._children)
        self._children.append(child)
        self._columncount = max(child.columnCount(), self._columncount)


class CustomModel(QtCore.QAbstractItemModel):
    def __init__(self, nodes):
        QtCore.QAbstractItemModel.__init__(self)
        self._root = CustomNode(None)
        for node in nodes:
            self._root.addChild(node)

    def rowCount(self, index):
        if index.isValid():
            return index.internalPointer().childCount()
        return self._root.childCount()

    def addChild(self, node, _parent):
        if not _parent or not _parent.isValid():
            parent = self._root
        else:
            parent = _parent.internalPointer()
        parent.addChild(node)

    def index(self, row, column, _parent=None):
        if not _parent or not _parent.isValid():
            parent = self._root
        else:
            parent = _parent.internalPointer()

        if not QtCore.QAbstractItemModel.hasIndex(self, row, column, _parent):
            return QtCore.QModelIndex()

        child = parent.child(row)
        if child:
            return QtCore.QAbstractItemModel.createIndex(self, row, column, child)
        else:
            return QtCore.QModelIndex()

    def parent(self, index):
        if index.isValid():
            p = index.internalPointer().parent()
            if p:
                return QtCore.QAbstractItemModel.createIndex(self, p.row(), 0, p)
        return QtCore.QModelIndex()

    def columnCount(self, index):
        if index.isValid():
            return index.internalPointer().columnCount()
        return self._root.columnCount()

    def data(self, index, role):
        if not index.isValid():
            return None
        node = index.internalPointer()
        if role == QtCore.Qt.DisplayRole:
            return node.data(index.column())
        return None


class MyTree():
    """
    """
    def __init__(self):
        self.items = []

        # Set some random data:
        for i in 'abc':
            self.items.append(CustomNode(i))
            self.items[-1].addChild(CustomNode(['d', 'e', 'f']))
            self.items[-1].addChild(CustomNode(['g', 'h', 'i']))

        self.tw = QtWidgets.QTreeView()
        self.tw.setModel(CustomModel(self.items))

    def add_data(self, data):
        """
        TODO: how to insert data, and update tree.
        """
        # self.items[-1].addChild(CustomNode(['1', '2', '3']))
        # self.tw.setModel(CustomModel(self.items))


if __name__ == "__main__":
    app = QtWidgets.QApplication(sys.argv)
    mytree = MyTree()
    mytree.tw.show()
    sys.exit(app.exec_())

I had a go at implementing the insert data method but ran into a bit of trouble. I'm doing exactly what the docs say but the QTreeView does not update after the insert. See here is you are interested, https://gist.github.com/danieljfarrell/6e94aa6f8c3c437d901fd15b7b931afb

# Get the model backing the tree widget
model = self.tw.model()
# Ask the model to generate an index for us. This is the index of the root item
rootIdx = model.index(0, 0, QtCore.QModelIndex())
# Pick an insert location for a new node. This should be based on some input. For example
# the location of a mouse click or the last element if we are appending. In this example
# I have hard coded a value.
position = 3
# Create a new node called and give it a name
new = CustomNode("new")
# Add a child node to the node which contains the value we want to display.
new.addChild(CustomNode(rowItems))

So far the we have created this:
# new
# |-- 1
# |---2
# |---3

# Now we need to insert this node into the model's tree.
# Don't quite understand all this Qt boilerplate...
model.beginInsertRows(rootIdx, position, position)
model.addChild(new, None)
model.endInsertRows()

# Now we have:
# + a
# + b
# + c
# + new
#   |-- 1
#   |--2
#   |--3

# This tells the view to redraw
model.layoutChanged.emit()
``

Does this implementation handle drag and drop?

Hello,
I have spent the whole afternoon studying your code and I still understand this :
How does the QModelIndex keep a reference to the underlying data.

For example if I want the retrieve the row = 2, col = 3 index, I would go for :

cm = CustomModel()
theQModelIndex = cm.index(2,3)
myData = cm.data(theQModelIndex, QtCore.Qt.DisplayRole)

And what I don't understand is here at the index.internalPointer()

    def data(self, index, role):
        if not index.isValid():
            return None
        node = index.internalPointer() # How does index.internalPointer() reference my node, I don't see anylink created before ???
        if role == QtCore.Qt.DisplayRole:
            return node.data(index.column())
        return None

It just seems like magic to me !