Add additional information to items in a QTreeView/QFileSystemModel

Question

I would like to render each item in a QTreeView differently based on a number of attributes stored in a database and based on whether the item is a folder or a file. However, I don't understand how the QTreeView or QFileSystemModel communicate with the delegate. Whenever an item must be drawn, including during initialization, I'd expect to provide the delegate with all the parameters it requires and then use a series of if statements within the delegate to set how the particular item is drawn. I've only found the .setItemDelegate method and don't know when or how the delegate is actually called or how it loops through all the items in the model. Below is an example based on material online. There are two problems:

1. I placed code in comments that I was unable to get working. Once I understand how the delegate can receive information from the QTreeView (or calling class), I believe I can do the rest.

2. I was unable to get this subclass of the QTreeView to display the folder and file icons.

Code:

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

class fileSystemDelegate(QItemDelegate):
    def __init__(self, parent=None):
        QItemDelegate.__init__(self, parent)        #shouldn't this insure the icons are drawn?

    def paint(self, painter, option, index):
        painter.save()

        # set background
        painter.setPen(QPen(Qt.NoPen))
        if option.state & QStyle.State_Selected:   #DURING DRAW LOOP: idx = self.currentIndex(); if self.fileSystemModel.isDir(idx): PAINT RED
            painter.setBrush(QBrush(Qt.red))
        else:
            painter.setBrush(QBrush(Qt.white))     #ELSE PAINT WHITE
        painter.drawRect(option.rect)

        # draw item
        painter.setPen(QPen(Qt.black))
        text = index.data(Qt.DisplayRole)
        painter.drawText(option.rect, Qt.AlignLeft, text)   #there is no painter.drawIcon?

        painter.restore()

class fileSystemBrowser(QTreeView):
    def __init__(self, parent=None):
        super().__init__(parent)

        delegate = fileSystemDelegate()
        self.setItemDelegate(delegate)                  # how to provide delegate with additional info about the item to be drawn ?

        self.fileSystemModel = QFileSystemModel()
        self.fileSystemModel.setRootPath(QDir.currentPath())
        self.setModel(self.fileSystemModel)

if __name__ == '__main__':

    app = QApplication(sys.argv)
    window = fileSystemBrowser()
    window.show()
    sys.exit(app.exec_())

EDIT 1:

I've added an example "database" in the form of a dictionary and changed the approach to rely on the data method rather than the delegate. I would expect this code to perform the dictionary lookup whenever information is displayed in the tree and therefore print to the terminal when the user enters C:\Program Files\Internet Explorer\ on a Microsoft Windows computer. However, it just displays the directory without printing anything to the terminal. I'd like to know:

1. How do I get if statements in the data method to trigger for every item in the display as they are being drawn?

2. How can I display an icon after the default icon is displayed, on the same row?

Code:

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

database = {'C:\Program Files\Internet Explorer\ExtExport.exe':(1,3), 'C:\Program Files\Internet Explorer\iexplore.exe':(0,0)}

class fileSystemBrowser(QTreeView):
    def __init__(self, parent=None):
        super().__init__(parent)

        self.fileSystemModel = QFileSystemModel()
        self.fileSystemModel.setRootPath(QDir.currentPath())
        self.setModel(self.fileSystemModel)

    def data(self, index, role=Qt.DisplayRole):
        if index.isValid():
            path = self.fileSystemModel.filePath(index)
            if  self.fileSystemModel.isDir(index):
                if database.get(path) != None:
                    if database[path][0] > 0:
                        print("Acting on custom data 0.") # add another icon after the regular folder icon

                    if database[path][1] > 0:
                        print("Acting on custom data 1.") # add another (different) icon after the regular folder or previous icon

if __name__ == '__main__':

    app = QApplication(sys.argv)
    window = fileSystemBrowser()
    window.show()
    sys.exit(app.exec_())

EDIT 2:

Subclassing the model definitely did make a difference. Now the script appears to be calling my new data method on every item. Unfortunately, the data method doesn't work yet so the result is a treeview without icons or text. Sometimes I receive the error: "QFileSystemWatcher: failed to add paths: C:/PerfLogs". Based on examples online, I've commented where I think my errors may be, but I cannot yet get this to work. What am I doing wrong?

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

database = {'C:\Program Files\Internet Explorer\ExtExport.exe':(1,3), 'C:\Program Files\Internet Explorer\iexplore.exe':(0,0)}

class newFileModel(QFileSystemModel):

    def __init__(self, parent=None):
        QFileSystemModel.__init__(self, parent)
        #self.elements = [[Do I need this? What should go here?]]

    def data(self, index, role=Qt.DisplayRole):
        if index.isValid():
            path = self.filePath(index)
            if  self.isDir(index):
                if database.get(path) != None:
                    if database[path][0] > 0:
                        print("Acting on custom data 0.") # I can add code here for different color text, etc.

                    if database[path][1] > 0:
                        print("Acting on custom data 1.") # I'll add code later
        #return self.data(index, role) # Do I need this about here?


class fileSystemBrowser(QTreeView):
    def __init__(self, parent=None):
        super().__init__(parent)

        self.fileSystemModel = newFileModel()
        self.fileSystemModel.setRootPath(QDir.currentPath())
        self.setModel(self.fileSystemModel)


if __name__ == '__main__':

    app = QApplication(sys.argv)
    window = fileSystemBrowser()
    window.show()
    sys.exit(app.exec_())

Answer 1

Here is a basic demo that shows how to add an extra column with icons and other formatting. Note that an attempt is made to normalise the file-paths so that comparisons and dictionary look-ups should be more reliable:

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

database = {
    QFileInfo('C:\Program Files\Internet Explorer\ExtExport.exe').absoluteFilePath(): (1, 3),
    QFileInfo('C:\Program Files\Internet Explorer\iexplore.exe').absoluteFilePath(): (0, 0),
    }

class FileSystemModel(QFileSystemModel):
    def __init__(self, parent=None):
        super().__init__(parent)
        style = qApp.style()
        self.icons = [
            style.standardIcon(QStyle.SP_MessageBoxInformation),
            style.standardIcon(QStyle.SP_MessageBoxWarning),
            ]

    def columnCount(self, parent=QModelIndex()):
        return super().columnCount(parent) + 1

    def data(self, index, role=Qt.DisplayRole):
        extra = False
        if index.isValid():
            extra = index.column() == self.columnCount(index.parent()) - 1
            info = self.fileInfo(index)
            path = info.absoluteFilePath()
            if path in database:
                major, minor = database[path]
                print('found:', (major, minor), path)
                if extra:
                    if role == Qt.DecorationRole:
                        if major > 0:
                            return self.icons[0]
                        else:
                            return self.icons[1]
                    elif role == Qt.DisplayRole:
                        return '%s/%s' % (major, minor)
                    elif role == Qt.ForegroundRole:
                        if minor > 2:
                            return QColor('red')
        if not extra:
            return super().data(index, role)

    def headerData(self, section, orientation, role=Qt.DisplayRole):
        if (orientation == Qt.Horizontal and
            role == Qt.DisplayRole and
            section == self.columnCount() - 1):
            return 'Extra'
        return super().headerData(section, orientation, role)

class FileSystemBrowser(QTreeView):
    def __init__(self, parent=None):
        super().__init__(parent)
        self.fileSystemModel = FileSystemModel()
        self.fileSystemModel.setRootPath(QDir.currentPath())
        self.setModel(self.fileSystemModel)
        self.header().moveSection(self.fileSystemModel.columnCount() - 1, 1)

if __name__ == '__main__':

    app = QApplication(sys.argv)
    window = FileSystemBrowser()
    window.show()
    sys.exit(app.exec_())

EDIT:

The roles used in the data method are all documented under the ItemDataRole enum, and are introduced as follows:

Each item in the model has a set of data elements associated with it, each with its own role. The roles are used by the view to indicate to the model which type of data it needs. Custom models should return data in these types.

For the extra column that has been added, it is necessary to supply everything, because it is a virtual column that is not part of the underlying model. But for the other columns, we can just call the base-class implementation to get the default values (of course, if desired, we could also return custom values for these columns to modify the existing behaviour).