lazy loading child items Qtreeview

Question

I am trying to load child items in a treeview

+top
  parent1
  parent2
  parent3

To start off I populate the model with parent node information only and attach it to a treeview, the tree looks like above.

self.mytreeview=QtGui.Qtreeview()
self.model=QtGui.QStandardItemModel(self.mytreeview)

def initialise_model(self):
    '''Populate the model with parent nodes only'''
    #open file and process each line, each file line has the parent node info
    ....

    for file_name_entry in fileobject:
        parent_item=QtGui.QStandardItem(str(file_name_entry).strip())
        parent_item.setData("this is a parent",QtCore.Qt.TooltipRole)
        self.model.appendRow(parent_item)
    self.mytreeview.setModel(self.model)

At this point none of the parents have any child information. What I want to do next is to update a parent node, when the user clicks on the parent node(just in time or lazy loading of a parents child information).

So when a parent node is clicked, and the signal is emitted

QtCore.QObject.connect(self.ui.treeView, QtCore.SIGNAL('clicked(QModelIndex)'), self.update_model)

update_model code should go fetch the children of that parent, update the model, refresh the tree and expand the parent node.

    def update_model(self,index):
        '''Update the model by adding children to selected/clicked parent node only'''
        parent_node=QtGui.QStandardItem(self.model.itemFromIndex(index))
        parent_item_index=index.row()
        #open the file called parent_node.txt and get all the child entries from the file...
        child_index=0
        for child_name_entry in parent_text_fileobject:
            child_item=QtGui.QStandardItem(str(child_name_entry).strip())
            child_item.setData("this is a child",QtCore.Qt.TooltipRole)
            parent_item.setChild(child_index,child_item)
            child_index=child_index+1
#Once all the children have been added update the model, by inserting a new row where the parent was
        self.model.removeRow(parent_item_index)#remove old parent
        self.model.insertRow(parent_item_index,parent_item)#insert new parent with its children

When I try to remove the selected parent node (the one with no children) and try inserting a new parent item (with children) it ends up addding the new parent(with children) above the parent node with no children so I end up with duplicated parent nodes

+top
  parent1
  parent2
  +parent2
    child_a
    child_b
    child_c  
  parent3

So just to recap, removing and inserting i.e.

#Once all the children have been added update the model, by inserting a new row where the parent was
        self.model.removeRow(parent_item_index)#remove old parent
        self.model.insertRow(parent_item_index,parent_item)#insert new parent with its children

is a bad idea. Looking at the comments its been suggested that AppendRow() might be the answer, but I am not so certain I believe that

self.model.appendRow(parent_item)#new parent with its children

Would simply add the parent to the bottom of my model and therefore the tree would still have duplicate parent nodes i.e

+top
  parent1
  **parent2**
  parent3
  **+parent2**
    child_a
    child_b
    child_c  

I think what I am looking for is a way to update an existing node in the model, so that the selected (parent node) can be updated with its children. e.g.

...
    self.model.UpdateExisitingNode(node_index)
...

Any suggestions on how to update an node in model? Note I am using Windows and PyQt

Regards

Answer 1

You are duplicating items because you are creating another parent item, you should only create new child items. For example:

from PyQt4 import QtGui


class Widget(QtGui.QWidget):
    def __init__(self, parent=None):
        QtGui.QWidget.__init__(self, parent)
        self.mytreeview = QtGui.QTreeView(self)
        self.setLayout(QtGui.QVBoxLayout())
        self.layout().addWidget(self.mytreeview)
        self.model = QtGui.QStandardItemModel(self.mytreeview)
        self.mytreeview.setModel(self.model)
        self.mytreeview.clicked.connect(self.update_model)
        self.initialise_model()

    def initialise_model(self):
        for text in ["parent1", "parent2", "parent3"]:
            item = QtGui.QStandardItem(text)
            self.model.appendRow(item)

    def update_model(self, index):
        parent = self.model.itemFromIndex(index)
        for text in ["children1", "children2", "children3"]:
            children = QtGui.QStandardItem("{}_{}".format(parent.text(), text))
            parent.appendRow(children)
        self.mytreeview.expand(index)


if __name__ == '__main__':
    import sys
    app = QtGui.QApplication(sys.argv)
    w = Widget()
    w.show()
    sys.exit(app.exec_())