Document Viewer Example

A Widgets application to display and print JSON, text, and PDF files.

Document Viewer demonstrates how to use a QMainWindow with static and dynamic toolbars, menus, and actions.

Download this example

abstractviewer.py

AbstractViewer provides a generalized API to view, save, and print a document. Properties of both the document and the viewer can be queried:

• Does the document have content?

• Has it been modified?

• Is an overview (thumbnails or bookmarks) supported?

AbstractViewer provides protected methods for derived classes to create actions and menus on the main window. In order to display these assets on the main window, they are parented to it. AbstractViewer is responsible for removing and destroying the UI assets it creates. It inherits from QObject to implement signals and slots.

The uiInitialized() signal is emitted after a viewer receives all necessary information about UI assets on the main window.

The printingEnabledChanged() signal is emitted when document printing is either enabled or disabled. This happens after a new document was successfully loaded, or, for example, all content was removed.

The printStatusChanged signal notifies about changes in its progress after starting the printing process.

The documentLoaded() signal notifies the application that a document was successfully loaded.

# Copyright (C) 2023 The Qt Company Ltd.
# SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause

from PySide6.QtCore import QObject

from PySide6.QtWidgets import (QDialog, QMenu)
from PySide6.QtCore import Signal, Slot
from PySide6.QtPrintSupport import QPrinter, QPrintDialog


MENU_NAME = "qtFileMenu"


class AbstractViewer(QObject):

    uiInitialized = Signal()
    printingEnabledChanged = Signal(bool)
    showMessage = Signal(str, int)
    documentLoaded = Signal(str)

    def __init__(self):
        super().__init__()
        self._file = None
        self._widget = None
        self._menus = []
        self._toolBars = []
        self._printingEnabled = False
        self._actions = []
        self._fileMenu = None

    def __del__(self):
        self.cleanup()

    def viewerName(self):
        return ""

    def saveState(self):
        return False

    def restoreState(self, state):
        return False

    def supportedMimeTypes():
        return []

    def init(self, file, widget, mainWindow):
        self._file = file
        self._widget = widget
        self._uiAssets_mainWindow = mainWindow

    def isEmpty(self):
        return not self.hasContent()

    def isPrintingEnabled(self):
        return self._printingEnabled

    def hasContent(self):
        return False

    def supportsOverview(self):
        return False

    def isModified(self):
        return False

    def saveDocument(self):
        return False

    def saveDocumentAs(self):
        return False

    def actions(self):
        return self._actions

    def widget(self):
        return self._widget

    def menus(self):
        return self._menus

    def mainWindow(self):
        return self._uiAssets_mainWindow

    def statusBar(self):
        return self.mainWindow().statusBar()

    def menuBar(self):
        return self.mainWindow().menuBar()

    def maybeEnablePrinting(self):
        self.maybeSetPrintingEnabled(True)

    def disablePrinting(self):
        self.maybeSetPrintingEnabled(False)

    def isDefaultViewer(self):
        return False

    def viewer(self):
        return self

    def statusMessage(self, message, type="", timeout=8000):
        msg = self.viewerName()
        if type:
            msg += "/" + type
        msg += ": " + message
        self.showMessage.emit(msg, timeout)

    def addToolBar(self, title):
        bar = self.mainWindow().addToolBar(title)
        name = title.replace(' ', '')
        bar.setObjectName(name)
        self._toolBars.append(bar)
        return bar

    def addMenu(self, title):
        menu = QMenu(title, self.menuBar())
        menu.setObjectName(title)
        self.menuBar().insertMenu(self._uiAssets_help, menu)
        self._menus.append(menu)
        return menu

    def cleanup(self):
        # delete all objects created by the viewer which need to be displayed
        # and therefore parented on MainWindow
        if self._file:
            self._file = None
        self._menus.clear()
        self._toolBars.clear()

    def fileMenu(self):
        if self._fileMenu:
            return self._fileMenu

        menus = self.mainWindow().findChildren(QMenu)
        for menu in menus:
            if menu.objectName() == MENU_NAME:
                self._fileMenu = menu
                return self._fileMenu
        self._fileMenu = self.addMenu("File")
        self._fileMenu.setObjectName(MENU_NAME)
        return self._fileMenu

    @Slot()
    def print_(self):
        type = "Printing"
        if not self.hasContent():
            self.statusMessage("No content to print.", type)
            return
        printer = QPrinter(QPrinter.HighResolution)
        dlg = QPrintDialog(printer, self.mainWindow())
        dlg.setWindowTitle("Print Document")
        if dlg.exec() == QDialog.Accepted:
            self.printDocument(printer)
        else:
            self.statusMessage("Printing canceled!", type)
            return
        state = printer.printerState()
        message = self.viewerName() + " :"
        if state == QPrinter.PrinterState.Aborted:
            message += "Printing aborted."
        elif state == QPrinter.PrinterState.Active:
            message += "Printing active."
        elif state == QPrinter.PrinterState.Idle:
            message += "Printing completed."
        elif state == QPrinter.PrinterState.Error:
            message += "Printing error."
        self.statusMessage(message, type)

    def maybeSetPrintingEnabled(self, enabled):
        if enabled == self._printingEnabled:
            return
        self._printingEnabled = enabled
        self.printingEnabledChanged.emit(enabled)

    def initViewer(self, back, forward, help, tabs):
        self._uiAssets_back = back
        self._uiAssets_forward = forward
        self._uiAssets_help = help
        self._uiAssets_tabs = tabs
        # Tabs can be populated individually by the viewer, if it
        # supports overview
        tabs.clear()
        tabs.setVisible(self.supportsOverview())
        self.uiInitialized.emit()

documentviewer.qrc

<!DOCTYPE RCC><RCC version="1.0">
<qresource prefix="demos/documentviewer">
    <file>images/copy@2x.png</file>
    <file>images/copy.png</file>
    <file>images/cut@2x.png</file>
    <file>images/cut.png</file>
    <file>images/go-next-view@2x.png</file>
    <file>images/go-next-view-page@2x.png</file>
    <file>images/go-next-view-page.png</file>
    <file>images/go-next-view.png</file>
    <file>images/go-previous-view@2x.png</file>
    <file>images/go-previous-view-page@2x.png</file>
    <file>images/go-previous-view-page.png</file>
    <file>images/go-previous-view.png</file>
    <file>images/magnifier@2x.png</file>
    <file>images/magnifier.png</file>
    <file>images/open@2x.png</file>
    <file>images/open.png</file>
    <file>images/paste@2x.png</file>
    <file>images/paste.png</file>
    <file>images/print2x.png</file>
    <file>images/print.png</file>
    <file>images/qt-logo@2x.png</file>
    <file>images/qt-logo.png</file>
    <file>images/zoom-fit-best@2x.png</file>
    <file>images/zoom-fit-best.png</file>
    <file>images/zoom-fit-width@2x.png</file>
    <file>images/zoom-fit-width.png</file>
    <file>images/zoom-in@2x.png</file>
    <file>images/zoom-in.png</file>
    <file>images/zoom-original@2x.png</file>
    <file>images/zoom-original.png</file>
    <file>images/zoom-out@2x.png</file>
    <file>images/zoom-out.png</file>
    <file>images/zoom-previous@2x.png</file>
    <file>images/zoom-previous.png</file>
    <file>images/document-open-recent.svgz</file>
    <file>images/go-next.svgz</file>
    <file>images/go-previous.svgz</file>
    <file>images/help-about.svgz</file>
</qresource>
</RCC>

main.py

# Copyright (C) 2023 The Qt Company Ltd.
# SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause

"""PySide6 port of the Qt Document Viewer demo from Qt v6.x"""

import sys
from argparse import ArgumentParser, RawTextHelpFormatter

from PySide6.QtWidgets import QApplication
from PySide6.QtCore import QCoreApplication

from mainwindow import MainWindow


DESCRIPTION = "A viewer for JSON, PDF and text files"


if __name__ == "__main__":

    app = QApplication([])
    QCoreApplication.setOrganizationName("QtExamples")
    QCoreApplication.setApplicationName("DocumentViewer")
    QCoreApplication.setApplicationVersion("1.0")

    arg_parser = ArgumentParser(description=DESCRIPTION,
                                formatter_class=RawTextHelpFormatter)
    arg_parser.add_argument("file", type=str, nargs="?",
                            help="JSON, PDF or text file to open")
    args = arg_parser.parse_args()
    fileName = args.file

    w = MainWindow()
    w.show()
    if args.file and not w.openFile(args.file):
        sys.exit(-1)

    sys.exit(app.exec())

mainwindow.py

The MainWindow class provides an application screen with menus, actions, and a toolbar. It can open a file, automatically detecting its content type. It also maintains a list of previously opened files, using QSettings to store and reload settings when launched. The MainWindow creates a suitable viewer for the opened file, based on its content type, and provides support for printing a document.

MainWindow's constructor initializes the user interface created in Qt Designer. The mainwindow.ui file provides a QTabWidget on the left, showing bookmarks and thumbnails. On the right, there is a QScrollArea for viewing file content.

# Copyright (C) 2023 The Qt Company Ltd.
# SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause

from PySide6.QtWidgets import (QDialog, QFileDialog, QMainWindow, QMessageBox)
from PySide6.QtCore import (QDir, QFile, QFileInfo, QSettings, Slot)

from ui_mainwindow import Ui_MainWindow
from viewerfactory import ViewerFactory
from recentfiles import RecentFiles
from recentfilemenu import RecentFileMenu


settingsDir = "WorkingDir"
settingsMainWindow = "MainWindow"
settingsViewers = "Viewers"
settingsFiles = "RecentFiles"


ABOUT_TEXT = """A Widgets application to display and print JSON,
text and PDF files. Demonstrates various features to use
in widget applications: Using QSettings, query and save
user preferences, manage file histories and control cursor
behavior when hovering over widgets.

"""


class MainWindow(QMainWindow):

    def __init__(self, parent=None):
        super().__init__(parent)
        self.ui = Ui_MainWindow()

        self._currentDir = QDir()
        self._viewer = None
        self._recentFiles = RecentFiles()

        self.ui.setupUi(self)
        self.ui.actionOpen.triggered.connect(self.onActionOpenTriggered)
        self.ui.actionAbout.triggered.connect(self.onActionAboutTriggered)
        self.ui.actionAboutQt.triggered.connect(self.onActionAboutQtTriggered)

        self._recentFiles = RecentFiles(self.ui.actionRecent)
        self._recentFiles.countChanged.connect(self._recentFilesCountChanged)

        self.readSettings()
        self._factory = ViewerFactory(self.ui.viewArea, self)
        viewers = ", ".join(self._factory.viewerNames())
        self.statusBar().showMessage(f'Available viewers: {viewers}')

        menu = RecentFileMenu(self, self._recentFiles)
        self.ui.actionRecent.setMenu(menu)
        menu.fileOpened.connect(self.openFile)
        button = self.ui.mainToolBar.widgetForAction(self.ui.actionRecent)
        if button:
            self.ui.actionRecent.triggered.connect(button.showMenu)

    @Slot(int)
    def _recentFilesCountChanged(self, count):
        self.ui.actionRecent.setText(f"{count} recent files")

    def closeEvent(self, event):
        self.saveSettings()

    @Slot(int)
    def onActionOpenTriggered(self):
        fileDialog = QFileDialog(self, "Open Document",
                                 self._currentDir.absolutePath())
        while (fileDialog.exec() == QDialog.Accepted
               and not self.openFile(fileDialog.selectedFiles()[0])):
            pass

    @Slot(str)
    def openFile(self, fileName):
        file = QFile(fileName)
        if not file.exists():
            nf = QDir.toNativeSeparators(fileName)
            self.statusBar().showMessage(f"File {nf} could not be opened")
            return False

        fileInfo = QFileInfo(file)
        self._currentDir = fileInfo.dir()
        self._recentFiles.addFile(fileInfo.absoluteFilePath())

        # If a viewer is already open, clean it up and save its settings
        self.resetViewer()
        self._viewer = self._factory.viewer(file)
        if not self._viewer:
            nf = QDir.toNativeSeparators(fileName)
            self.statusBar().showMessage(f"File {nf} can't be opened.")
            return False

        self.ui.actionPrint.setEnabled(self._viewer.hasContent())
        self._viewer.printingEnabledChanged.connect(self.ui.actionPrint.setEnabled)
        self.ui.actionPrint.triggered.connect(self._viewer.print_)
        self._viewer.showMessage.connect(self.statusBar().showMessage)

        self._viewer.initViewer(self.ui.actionBack, self.ui.actionForward,
                                self.ui.menuHelp.menuAction(),
                                self.ui.tabWidget)
        self.restoreViewerSettings()
        self.ui.scrollArea.setWidget(self._viewer.widget())
        return True

    @Slot()
    def onActionAboutTriggered(self):
        viewerNames = ", ".join(self._factory.viewerNames())
        mimeTypes = '\n'.join(self._factory.supportedMimeTypes())
        text = ABOUT_TEXT
        text += f"\nThis version has loaded the following plugins:\n{viewerNames}\n"
        text += f"\n\nIt supports the following mime types:\n{mimeTypes}"

        defaultViewer = self._factory.defaultViewer()
        if defaultViewer:
            n = defaultViewer.viewerName()
            text += f"\n\nOther mime types will be displayed with {n}."

        QMessageBox.about(self, "About Document Viewer Demo", text)

    @Slot()
    def onActionAboutQtTriggered(self):
        QMessageBox.aboutQt(self)

    def readSettings(self):
        settings = QSettings()

        # Restore working directory
        if settings.contains(settingsDir):
            self._currentDir = QDir(settings.value(settingsDir))
        else:
            self._currentDir = QDir.current()

        # Restore QMainWindow state
        if settings.contains(settingsMainWindow):
            mainWindowState = settings.value(settingsMainWindow)
            self.restoreState(mainWindowState)

        # Restore recent files
        self._recentFiles.restoreFromSettings(settings, settingsFiles)

    def saveSettings(self):
        settings = QSettings()

        # Save working directory
        settings.setValue(settingsDir, self._currentDir.absolutePath())

        # Save QMainWindow state
        settings.setValue(settingsMainWindow, self.saveState())

        # Save recent files
        self._recentFiles.saveSettings(settings, settingsFiles)

        settings.sync()

    def saveViewerSettings(self):
        if not self._viewer:
            return
        settings = QSettings()
        settings.beginGroup(settingsViewers)
        settings.setValue(self._viewer.viewerName(), self._viewer.saveState())
        settings.endGroup()
        settings.sync()

    def resetViewer(self):
        if not self._viewer:
            return
        self.saveViewerSettings()
        self._viewer.cleanup()

    def restoreViewerSettings(self):
        if not self._viewer:
            return
        settings = QSettings()
        settings.beginGroup(settingsViewers)
        viewerSettings = settings.value(self._viewer.viewerName())
        settings.endGroup()
        if viewerSettings:
            self._viewer.restoreState(viewerSettings)

mainwindow.ui

<?xml version="1.0" encoding="UTF-8"?>
<ui version="4.0">
 <class>MainWindow</class>
 <widget class="QMainWindow" name="MainWindow">
  <property name="geometry">
   <rect>
    <x>0</x>
    <y>0</y>
    <width>983</width>
    <height>602</height>
   </rect>
  </property>
  <property name="windowTitle">
   <string>Document Viewer Demo</string>
  </property>
  <property name="windowIcon">
   <iconset resource="documentviewer.qrc">
    <normaloff>:/demos/documentviewer/images/qt-logo.png</normaloff>:/demos/documentviewer/images/qt-logo.png</iconset>
  </property>
  <widget class="QWidget" name="centralwidget">
   <property name="enabled">
    <bool>true</bool>
   </property>
   <layout class="QVBoxLayout" name="verticalLayout">
    <item>
     <widget class="QWidget" name="viewArea" native="true">
      <layout class="QVBoxLayout" name="verticalLayout_2">
       <item>
        <widget class="QSplitter" name="splitter">
         <property name="orientation">
          <enum>Qt::Horizontal</enum>
         </property>
         <widget class="QTabWidget" name="tabWidget">
          <property name="tabPosition">
           <enum>QTabWidget::West</enum>
          </property>
          <property name="currentIndex">
           <number>0</number>
          </property>
          <widget class="QWidget" name="bookmarkTab">
           <attribute name="title">
            <string>Pages</string>
           </attribute>
          </widget>
          <widget class="QWidget" name="pagesTab">
           <attribute name="title">
            <string>Bookmarks</string>
           </attribute>
          </widget>
         </widget>
         <widget class="QScrollArea" name="scrollArea">
          <property name="sizePolicy">
           <sizepolicy hsizetype="Expanding" vsizetype="Expanding">
            <horstretch>0</horstretch>
            <verstretch>0</verstretch>
           </sizepolicy>
          </property>
          <property name="minimumSize">
           <size>
            <width>800</width>
            <height>0</height>
           </size>
          </property>
          <property name="widgetResizable">
           <bool>true</bool>
          </property>
          <widget class="QWidget" name="scrollAreaWidgetContents">
           <property name="geometry">
            <rect>
             <x>0</x>
             <y>0</y>
             <width>798</width>
             <height>479</height>
            </rect>
           </property>
          </widget>
         </widget>
        </widget>
       </item>
      </layout>
     </widget>
    </item>
   </layout>
  </widget>
  <widget class="QMenuBar" name="menubar">
   <property name="geometry">
    <rect>
     <x>0</x>
     <y>0</y>
     <width>983</width>
     <height>23</height>
    </rect>
   </property>
   <widget class="QMenu" name="qtFileMenu">
    <property name="title">
     <string>File</string>
    </property>
    <addaction name="actionOpen"/>
    <addaction name="actionRecent"/>
    <addaction name="actionPrint"/>
    <addaction name="actionQuit"/>
   </widget>
   <widget class="QMenu" name="menuHelp">
    <property name="title">
     <string>Help</string>
    </property>
    <addaction name="actionAbout"/>
    <addaction name="actionAboutQt"/>
   </widget>
   <addaction name="qtFileMenu"/>
   <addaction name="menuHelp"/>
  </widget>
  <widget class="QStatusBar" name="statusbar"/>
  <widget class="QToolBar" name="mainToolBar">
   <property name="windowTitle">
    <string>toolBar</string>
   </property>
   <attribute name="toolBarArea">
    <enum>TopToolBarArea</enum>
   </attribute>
   <attribute name="toolBarBreak">
    <bool>false</bool>
   </attribute>
   <addaction name="actionOpen"/>
   <addaction name="actionRecent"/>
   <addaction name="actionPrint"/>
   <addaction name="separator"/>
   <addaction name="actionBack"/>
   <addaction name="actionForward"/>
   <addaction name="separator"/>
  </widget>
  <action name="actionOpen">
   <property name="icon">
    <iconset resource="documentviewer.qrc">
     <normaloff>:/demos/documentviewer/images/open.png</normaloff>:/demos/documentviewer/images/open.png</iconset>
   </property>
   <property name="text">
    <string>Open</string>
   </property>
   <property name="shortcut">
    <string>Ctrl+O</string>
   </property>
  </action>
  <action name="actionAbout">
   <property name="icon">
    <iconset theme="help-about" resource="documentviewer.qrc">
     <normaloff>:/demos/documentviewer/images/help-about.svgz</normaloff>:/demos/documentviewer/images/help-about.svgz</iconset>
   </property>
   <property name="text">
    <string>about documentviewer</string>
   </property>
   <property name="toolTip">
    <string>Show information about the Document Viewer deomo.</string>
   </property>
   <property name="shortcut">
    <string>Ctrl+H</string>
   </property>
  </action>
  <action name="actionForward">
   <property name="icon">
    <iconset resource="documentviewer.qrc">
     <normaloff>:/demos/documentviewer/images/go-next.svgz</normaloff>:/demos/documentviewer/images/go-next.svgz</iconset>
   </property>
   <property name="text">
    <string>actionForward</string>
   </property>
   <property name="toolTip">
    <string>One step forward</string>
   </property>
   <property name="shortcut">
    <string>Right</string>
   </property>
  </action>
  <action name="actionBack">
   <property name="icon">
    <iconset resource="documentviewer.qrc">
     <normaloff>:/demos/documentviewer/images/go-previous.svgz</normaloff>:/demos/documentviewer/images/go-previous.svgz</iconset>
   </property>
   <property name="text">
    <string>actionBack</string>
   </property>
   <property name="toolTip">
    <string>One step back</string>
   </property>
   <property name="shortcut">
    <string>Left</string>
   </property>
  </action>
  <action name="actionPrint">
   <property name="enabled">
    <bool>false</bool>
   </property>
   <property name="icon">
    <iconset theme="document-print" resource="documentviewer.qrc">
     <normaloff>:/demos/documentviewer/images/print2x.png</normaloff>:/demos/documentviewer/images/print2x.png</iconset>
   </property>
   <property name="text">
    <string>Print</string>
   </property>
   <property name="toolTip">
    <string>Print current file</string>
   </property>
   <property name="shortcut">
    <string>Ctrl+P</string>
   </property>
  </action>
  <action name="actionAboutQt">
   <property name="icon">
    <iconset resource="documentviewer.qrc">
     <normaloff>:/demos/documentviewer/images/qt-logo.png</normaloff>
     <normalon>:/demos/documentviewer/images/qt-logo.png</normalon>:/demos/documentviewer/images/qt-logo.png</iconset>
   </property>
   <property name="text">
    <string>About Qt</string>
   </property>
   <property name="toolTip">
    <string>Show Qt license information</string>
   </property>
   <property name="shortcut">
    <string>Ctrl+I</string>
   </property>
  </action>
  <action name="actionRecent">
   <property name="icon">
    <iconset resource="documentviewer.qrc">
     <normaloff>:/demos/documentviewer/images/document-open-recent.svgz</normaloff>:/demos/documentviewer/images/document-open-recent.svgz</iconset>
   </property>
   <property name="text">
    <string>Recently opened...</string>
   </property>
   <property name="shortcut">
    <string>Meta+R</string>
   </property>
  </action>
  <action name="actionQuit">
   <property name="icon">
    <iconset theme="application-exit">
     <normaloff>.</normaloff>.</iconset>
   </property>
   <property name="text">
    <string>Quit</string>
   </property>
   <property name="toolTip">
    <string>Quit the application</string>
   </property>
   <property name="shortcut">
    <string>Ctrl+Q</string>
   </property>
  </action>
 </widget>
 <resources>
  <include location="documentviewer.qrc"/>
 </resources>
 <connections>
  <connection>
   <sender>actionQuit</sender>
   <signal>triggered()</signal>
   <receiver>MainWindow</receiver>
   <slot>close()</slot>
   <hints>
    <hint type="sourcelabel">
     <x>-1</x>
     <y>-1</y>
    </hint>
    <hint type="destinationlabel">
     <x>491</x>
     <y>300</y>
    </hint>
   </hints>
  </connection>
 </connections>
</ui>

jsonviewer/jsonviewer.py

JsonViewer displays a JSON file in a QTreeView. Internally, it loads the contents of a file into a data structure via a string and uses it to populate a custom tree model with JsonItemModel.

The JSON viewer demonstrates how to implement a custom item model inherited from QAbstractItemModel.

JsonViewer uses the top-level objects of the document as bookmarks for navigation. Other nodes (keys and values) can be added as additional bookmarks, or removed from the bookmark list. A QLineEdit is used as a search field to navigate through the JSON tree.

# Copyright (C) 2023 The Qt Company Ltd.
# SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause

import json

from PySide6.QtWidgets import (QLabel, QLineEdit, QListWidget,
                               QListWidgetItem, QMenu, QTreeView)
from PySide6.QtGui import (QAction, QIcon, QKeySequence,
                           QPixmap, QTextDocument)
from PySide6.QtCore import (QAbstractItemModel, QDir,
                            QIODevice, QModelIndex,
                            QPoint, QSize, Qt, Slot)

from abstractviewer import AbstractViewer


def resizeToContents(tree):
    for i in range(0, tree.header().count()):
        tree.resizeColumnToContents(i)


class JsonTreeItem:

    def __init__(self, parent=None):
        self._key = ""
        self._value = None
        self._children = []
        self._parent = parent

    def key(self):
        return self._key

    def value(self):
        return self._value

    def appendChild(self, item):
        self._children.append(item)

    def child(self, row):
        return self._children[row]

    def parent(self):
        return self._parent

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

    def row(self):
        if self._parent:
            return self._parent._children.index(self)
        return 0

    def setKey(self, key):
        self._key = key

    def setValue(self, value):
        self._value = value

    @staticmethod
    def load(value, parent=None):
        rootItem = JsonTreeItem(parent)
        rootItem.setKey("root")

        if isinstance(value, dict):
            for key, val in value.items():
                child = JsonTreeItem.load(val, rootItem)
                child.setKey(key)
                rootItem.appendChild(child)

        elif isinstance(value, list):
            for index, val in enumerate(value):
                child = JsonTreeItem.load(val, rootItem)
                child.setKey(f"{index}")
                rootItem.appendChild(child)

        else:
            rootItem.setValue(value)

        return rootItem


class JsonItemModel(QAbstractItemModel):

    def columnCount(self, index=QModelIndex()):
        return 2

    def itemFromIndex(self, index):
        return index.internalPointer()

    def __init__(self, doc, parent):
        super().__init__(parent)
        self._textItem = JsonTreeItem()

        # Append header lines
        self._headers = ["Key", "Value"]

        # Reset the model. Root can either be a value or an array.
        self.beginResetModel()
        self._textItem = JsonTreeItem.load(doc) if doc else JsonTreeItem()
        self.endResetModel()

    def data(self, index, role):
        if not index.isValid():
            return None

        item = self.itemFromIndex(index)
        if role == Qt.DisplayRole:
            if index.column() == 0:
                return item.key()
            if index.column() == 1:
                return item.value()
        elif role == Qt.EditRole:
            if index.column() == 1:
                return item.value()
        return None

    def headerData(self, section, orientation, role):
        return (self._headers[section]
                if role == Qt.DisplayRole and orientation == Qt.Horizontal else None)

    def index(self, row, column, parent=QModelIndex()):
        if not self.hasIndex(row, column, parent):
            return None

        parentItem = JsonTreeItem()

        if not parent.isValid():
            parentItem = self._textItem
        else:
            parentItem = self.itemFromIndex(parent)

        childItem = parentItem.child(row)
        if childItem:
            return self.createIndex(row, column, childItem)
        return None

    def parent(self, index):
        if not index.isValid():
            return None

        childItem = self.itemFromIndex(index)
        parentItem = childItem.parent()

        if parentItem == self._textItem:
            return QModelIndex()

        return self.createIndex(parentItem.row(), 0, parentItem)

    def rowCount(self, parent=QModelIndex()):
        parentItem = JsonTreeItem()
        if parent.column() > 0:
            return 0

        if not parent.isValid():
            parentItem = self._textItem
        else:
            parentItem = self.itemFromIndex(parent)
        return parentItem.childCount()


class JsonViewer(AbstractViewer):

    def __init__(self):
        super().__init__()
        self._tree = QTreeView()
        self._toplevel = None
        self._text = ""
        self._searchKey = None
        self.uiInitialized.connect(self.setupJsonUi)

    def init(self, file, parent, mainWindow):
        self._tree = QTreeView(parent)
        super().init(file, self._tree, mainWindow)

    def viewerName(self):
        return "JsonViewer"

    def supportedMimeTypes(self):
        return ["application/json"]

    @Slot()
    def setupJsonUi(self):
        # Build Menus and toolbars
        menu = self.addMenu("Json")
        tb = self.addToolBar("Json Actions")

        zoomInIcon = QIcon.fromTheme(QIcon.ThemeIcon.ZoomIn)
        a = menu.addAction(zoomInIcon, "&+Expand all", self._tree.expandAll)
        tb.addAction(a)
        a.setPriority(QAction.LowPriority)
        a.setShortcut(QKeySequence.New)

        zoomOutIcon = QIcon.fromTheme(QIcon.ThemeIcon.ZoomOut)
        a = menu.addAction(zoomOutIcon, "&-Collapse all", self._tree.collapseAll)
        tb.addAction(a)
        a.setPriority(QAction.LowPriority)
        a.setShortcut(QKeySequence.New)

        if not self._searchKey:
            self._searchKey = QLineEdit(tb)

        label = QLabel(tb)
        magnifier = QPixmap(":/icons/images/magnifier.png").scaled(QSize(28, 28))
        label.setPixmap(magnifier)
        tb.addWidget(label)
        tb.addWidget(self._searchKey)
        self._searchKey.textEdited.connect(self._tree.keyboardSearch)

        if not self.openJsonFile():
            return

        # Populate bookmarks with toplevel
        self._uiAssets_tabs.clear()
        self._toplevel = QListWidget(self._uiAssets_tabs)
        self._uiAssets_tabs.addTab(self._toplevel, "Bookmarks")
        for i in range(0, self._tree.model().rowCount()):
            index = self._tree.model().index(i, 0)
            self._toplevel.addItem(index.data())
            item = self._toplevel.item(i)
            item.setData(Qt.UserRole, index)
            item.setToolTip(f"Toplevel Item {i}")

        self._toplevel.setAcceptDrops(True)
        self._tree.setDragEnabled(True)
        self._tree.setContextMenuPolicy(Qt.CustomContextMenu)
        self._toplevel.setContextMenuPolicy(Qt.CustomContextMenu)

        self._toplevel.itemClicked.connect(self.onTopLevelItemClicked)
        self._toplevel.itemDoubleClicked.connect(self.onTopLevelItemDoubleClicked)
        self._toplevel.customContextMenuRequested.connect(self.onBookmarkMenuRequested)
        self._tree.customContextMenuRequested.connect(self.onJsonMenuRequested)

        # Connect back and forward
        self._uiAssets_back.triggered.connect(self._back)
        self._uiAssets_forward.triggered.connect(self._forward)

    @Slot()
    def _back(self):
        index = self._tree.indexAbove(self._tree.currentIndex())
        if index.isValid():
            self._tree.setCurrentIndex(index)

    @Slot()
    def _forward(self):
        current = self._tree.currentIndex()
        next = self._tree.indexBelow(current)
        if next.isValid():
            self._tree.setCurrentIndex(next)
            return
        # Expand last item to go beyond
        if not self._tree.isExpanded(current):
            self._tree.expand(current)
            next = self._tree.indexBelow(current)
            if next.isValid():
                self._tree.setCurrentIndex(next)

    def openJsonFile(self):
        self.disablePrinting()
        file_name = QDir.toNativeSeparators(self._file.fileName())
        type = "open"
        self._file.open(QIODevice.ReadOnly)
        self._text = self._file.readAll().data().decode("utf-8")
        self._file.close()

        data = None
        message = None
        try:
            data = json.loads(self._text)
            message = f"Json document {file_name} opened"
            model = JsonItemModel(data, self)
            self._tree.setModel(model)
        except ValueError as e:
            message = f"Unable to parse Json document from {file_name}: {e}"
        self.statusMessage(message, type)
        self.maybeEnablePrinting()

        return self._tree.model() is not None

    def indexOf(self, item):
        return QModelIndex(item.data(Qt.UserRole))

    @Slot(QListWidgetItem)
    def onTopLevelItemClicked(self, item):
        """Move to the clicked toplevel index"""
        # return in the unlikely case that the tree has not been built
        if not self._tree.model():
            return

        index = self.indexOf(item)
        if not index.isValid():
            return

        self._tree.setCurrentIndex(index)

    @Slot(QListWidgetItem)
    def onTopLevelItemDoubleClicked(self, item):
        """Toggle double clicked index between collaps/expand"""

        # return in the unlikely case that the tree has not been built
        if not self._tree.model():
            return

        index = self.indexOf(item)
        if not index.isValid():
            return

        if self._tree.isExpanded(index):
            self._tree.collapse(index)
            return

        # Make sure the node and all parents are expanded
        while index.isValid():
            self._tree.expand(index)
            index = index.parent()

    @Slot(QPoint)
    def onJsonMenuRequested(self, pos):
        index = self._tree.indexAt(pos)
        if not index.isValid():
            return

        # Don't show a context menu, if the index is already a bookmark
        for i in range(0, self._toplevel.count()):
            if self.indexOf(self._toplevel.item(i)) == index:
                return

        menu = QMenu(self._tree)
        action = QAction("Add bookmark")
        action.setData(index)
        menu.addAction(action)
        action.triggered.connect(self.onBookmarkAdded)
        menu.exec(self._tree.mapToGlobal(pos))

    @Slot(QPoint)
    def onBookmarkMenuRequested(self, pos):
        item = self._toplevel.itemAt(pos)
        if not item:
            return

        # Don't delete toplevel items
        index = self.indexOf(item)
        if not index.parent().isValid():
            return

        menu = QMenu()
        action = QAction("Delete bookmark")
        action.setData(self._toplevel.row(item))
        menu.addAction(action)
        action.triggered.connect(self.onBookmarkDeleted)
        menu.exec(self._toplevel.mapToGlobal(pos))

    @Slot()
    def onBookmarkAdded(self):
        action = self.sender()
        if not action:
            return

        index = action.data()
        if not index.isValid():
            return

        item = QListWidgetItem(index.data(Qt.DisplayRole), self._toplevel)
        item.setData(Qt.UserRole, index)

        # Set a tooltip that shows where the item is located in the tree
        parent = index.parent()
        tooltip = index.data(Qt.DisplayRole).toString()
        while parent.isValid():
            tooltip = parent.data(Qt.DisplayRole).toString() + "." + tooltip
            parent = parent.parent()

        item.setToolTip(tooltip)

    @Slot()
    def onBookmarkDeleted(self):
        action = self.sender()
        if not action:
            return

        row = action.data().toInt()
        if row < 0 or row >= self._toplevel.count():
            return

        self._toplevel.takeItem(row)

    def hasContent(self):
        return bool(self._text)

    def supportsOverview(self):
        return True

    def printDocument(self, printer):
        if not self.hasContent():
            return
        doc = QTextDocument(self._text)
        doc.print_(printer)

pdfviewer/pdfviewer.py

# Copyright (C) 2023 The Qt Company Ltd.
# SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause

from math import sqrt

from PySide6.QtWidgets import (QListView, QTreeView)
from PySide6.QtGui import QIcon, QPainter
from PySide6.QtCore import (QDir, QIODevice, QModelIndex,
                            QPointF, Slot)
from PySide6.QtPrintSupport import QPrinter
from PySide6.QtPdf import QPdfDocument, QPdfBookmarkModel
from PySide6.QtPdfWidgets import QPdfView, QPdfPageSelector

from abstractviewer import AbstractViewer
from pdfviewer.zoomselector import ZoomSelector


ZOOM_MULTIPLIER = sqrt(2.0)


class PdfViewer(AbstractViewer):

    def __init__(self):
        super().__init__()
        self.uiInitialized.connect(self.initPdfViewer)
        self._toolBar = None
        self._zoomSelector = None
        self._pageSelector = None
        self._document = None
        self._pdfView = None
        self._actionForward = None
        self._actionBack = None
        self._bookmarks = None
        self._pages = None

    def init(self, file, parent, mainWindow):
        self._pdfView = QPdfView(parent)
        super().init(file, self._pdfView, mainWindow)
        self._document = QPdfDocument(self)

    def supportedMimeTypes(self):
        return ["application/pdf"]

    def initPdfViewer(self):
        self._toolBar = self.addToolBar("PDF")
        self._zoomSelector = ZoomSelector(self._toolBar)

        nav = self._pdfView.pageNavigator()
        self._pageSelector = QPdfPageSelector(self._toolBar)
        self._toolBar.insertWidget(self._uiAssets_forward, self._pageSelector)
        self._pageSelector.setDocument(self._document)
        self._pageSelector.currentPageChanged.connect(self.pageSelected)
        nav.currentPageChanged.connect(self._pageSelector.setCurrentPage)
        nav.backAvailableChanged.connect(self._uiAssets_back.setEnabled)
        self._actionBack = self._uiAssets_back
        self._actionForward = self._uiAssets_forward
        self._uiAssets_back.triggered.connect(self.onActionBackTriggered)
        self._uiAssets_forward.triggered.connect(self.onActionForwardTriggered)

        self._toolBar.addSeparator()
        self._toolBar.addWidget(self._zoomSelector)

        actionZoomIn = self._toolBar.addAction("Zoom in")
        actionZoomIn.setToolTip("Increase zoom level")
        icon = QIcon.fromTheme(QIcon.ThemeIcon.ZoomIn,
                               QIcon(":/demos/documentviewer/images/zoom-in.png"))
        actionZoomIn.setIcon(icon)
        self._toolBar.addAction(actionZoomIn)
        actionZoomIn.triggered.connect(self.onActionZoomInTriggered)

        actionZoomOut = self._toolBar.addAction("Zoom out")
        actionZoomOut.setToolTip("Decrease zoom level")
        icon = QIcon.fromTheme(QIcon.ThemeIcon.ZoomIn,
                               QIcon(":/demos/documentviewer/images/zoom-out.png"))
        actionZoomOut.setIcon(icon)
        self._toolBar.addAction(actionZoomOut)
        actionZoomOut.triggered.connect(self.onActionZoomOutTriggered)

        nav.backAvailableChanged.connect(self._actionBack.setEnabled)
        nav.forwardAvailableChanged.connect(self._actionForward.setEnabled)

        self._zoomSelector.zoomModeChanged.connect(self._pdfView.setZoomMode)
        self._zoomSelector.zoomFactorChanged.connect(self._pdfView.setZoomFactor)
        self._zoomSelector.reset()

        bookmarkModel = QPdfBookmarkModel(self)
        bookmarkModel.setDocument(self._document)
        self._uiAssets_tabs.clear()
        self._bookmarks = QTreeView(self._uiAssets_tabs)
        self._bookmarks.activated.connect(self.bookmarkSelected)
        self._bookmarks.setModel(bookmarkModel)
        self._pdfView.setDocument(self._document)
        self._pdfView.setPageMode(QPdfView.PageMode.MultiPage)

        self.openPdfFile()
        if not self._document.pageCount():
            return

        self._pages = QListView(self._uiAssets_tabs)
        self._pages.setModel(self._document.pageModel())

        self._pages.selectionModel().currentRowChanged.connect(self._currentRowChanged)
        self._pdfView.pageNavigator().currentPageChanged.connect(self._pageChanged)

        self._uiAssets_tabs.addTab(self._pages, "Pages")
        self._uiAssets_tabs.addTab(self._bookmarks, "Bookmarks")

    def viewerName(self):
        return "PdfViewer"

    @Slot(QModelIndex, QModelIndex)
    def _currentRowChanged(self, current, previous):
        if previous == current:
            return

        nav = self._pdfView.pageNavigator()
        row = current.row()
        if nav.currentPage() == row:
            return
        nav.jump(row, QPointF(), nav.currentZoom())

    @Slot(int)
    def _pageChanged(self, page):
        if self._pages.currentIndex().row() == page:
            return
        self._pages.setCurrentIndex(self._pages.model().index(page, 0))

    @Slot()
    def openPdfFile(self):
        self.disablePrinting()

        if self._file.open(QIODevice.ReadOnly):
            self._document.load(self._file)

        documentTitle = self._document.metaData(QPdfDocument.MetaDataField.Title)
        if not documentTitle:
            documentTitle = "PDF Viewer"
        self.statusMessage(documentTitle)
        self.pageSelected(0)

        file_name = QDir.toNativeSeparators(self._file.fileName())
        self.statusMessage(f"Opened PDF file {file_name}")
        self.maybeEnablePrinting()

    def hasContent(self):
        return self._document if self._document.pageCount() > 0 else False

    def supportsOverview(self):
        return True

    def printDocument(self, printer):
        if not self.hasContent():
            return

        painter = QPainter()
        painter.begin(printer)
        pageRect = printer.pageRect(QPrinter.Unit.DevicePixel).toRect()
        pageSize = pageRect.size()
        for i in range(0, self._document.pageCount()):
            if i > 0:
                printer.newPage()
            page = self._document.render(i, pageSize)
            painter.drawImage(pageRect, page)
        painter.end()

    @Slot(QModelIndex)
    def bookmarkSelected(self, index):
        if not index.isValid():
            return

        page = index.data(int(QPdfBookmarkModel.Role.Page))
        zoomLevel = index.data(int(QPdfBookmarkModel.Role.Level)).toReal()
        self._pdfView.pageNavigator().jump(page, QPointF(), zoomLevel)

    @Slot(int)
    def pageSelected(self, page):
        nav = self._pdfView.pageNavigator()
        nav.jump(page, QPointF(), nav.currentZoom())

    @Slot()
    def onActionZoomInTriggered(self):
        self._pdfView.setZoomFactor(self._pdfView.zoomFactor() * ZOOM_MULTIPLIER)

    @Slot()
    def onActionZoomOutTriggered(self):
        self._pdfView.setZoomFactor(self._pdfView.zoomFactor() / ZOOM_MULTIPLIER)

    @Slot()
    def onActionPreviousPageTriggered(self):
        nav = self._pdfView.pageNavigator()
        nav.jump(nav.currentPage() - 1, QPointF(), nav.currentZoom())

    @Slot()
    def onActionNextPageTriggered(self):
        nav = self._pdfView.pageNavigator()
        nav.jump(nav.currentPage() + 1, QPointF(), nav.currentZoom())

    @Slot()
    def onActionBackTriggered(self):
        self._pdfView.pageNavigator().back()

    @Slot()
    def onActionForwardTriggered(self):
        self._pdfView.pageNavigator().forward()

pdfviewer/zoomselector.py

# Copyright (C) 2017 Klaralvdalens Datakonsult AB (KDAB).
# SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause

from PySide6.QtWidgets import QComboBox
from PySide6.QtCore import Signal, Slot
from PySide6.QtPdfWidgets import QPdfView


ZOOM_LEVELS = ["Fit Width", "Fit Page", "12%", "25%", "33%", "50%", "66%",
               "75%", "100%", "125%", "150%", "200%", "400%"]


class ZoomSelector(QComboBox):
    zoomModeChanged = Signal(QPdfView.ZoomMode)
    zoomFactorChanged = Signal(float)

    def __init__(self, parent):
        super().__init__(parent)
        self.setEditable(True)

        for z in ZOOM_LEVELS:
            self.addItem(z)

        self.currentTextChanged.connect(self.onCurrentTextChanged)
        self.lineEdit().editingFinished.connect(self._editingFinished)

    @Slot()
    def _editingFinished(self):
        self.onCurrentTextChanged(self.lineEdit().text())

    @Slot(float)
    def setZoomFactor(self, zoomFactor):
        z = int(100 * zoomFactor)
        self.setCurrentText(f"{z}%")

    @Slot()
    def reset(self):
        self.setCurrentIndex(8)  # 100%

    @Slot(str)
    def onCurrentTextChanged(self, text):
        if text == "Fit Width":
            self.zoomModeChanged.emit(QPdfView.ZoomMode.FitToWidth)
        elif text == "Fit Page":
            self.zoomModeChanged.emit(QPdfView.ZoomMode.FitInView)
        else:
            factor = 1.0
            withoutPercent = text.replace('%', '')
            zoomLevel = int(withoutPercent)
            if zoomLevel:
                factor = zoomLevel / 100.0

            self.zoomModeChanged.emit(QPdfView.ZoomMode.Custom)
            self.zoomFactorChanged.emit(factor)

txtviewer/txtviewer.py

# Copyright (C) 2023 The Qt Company Ltd.
# SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause

from PySide6.QtWidgets import (QDialog, QFileDialog,
                               QPlainTextEdit)
from PySide6.QtGui import QAction, QGuiApplication, QIcon, QKeySequence
from PySide6.QtCore import QDir, QFile, QTextStream, Qt, Slot

from abstractviewer import AbstractViewer


class TxtViewer(AbstractViewer):
    def __init__(self):
        super().__init__()
        self.uiInitialized.connect(self.setupTxtUi)

    def init(self, file, parent, mainWindow):
        self._textEdit = QPlainTextEdit(parent)
        super().init(file, self._textEdit, mainWindow)

    def viewerName(self):
        return "TxtViewer"

    def supportedMimeTypes(self):
        return ["text/plain"]

    @Slot()
    def setupTxtUi(self):
        editMenu = self.addMenu("Edit")
        editToolBar = self.addToolBar("Edit")
        cutIcon = QIcon.fromTheme(QIcon.ThemeIcon.EditCut,
                                  QIcon(":/demos/documentviewer/images/cut.png"))
        cutAct = QAction(cutIcon, "Cut", self)
        cutAct.setShortcuts(QKeySequence.Cut)
        cutAct.setStatusTip("Cut the current selection's contents to the clipboard")
        cutAct.triggered.connect(self._textEdit.cut)
        editMenu.addAction(cutAct)
        editToolBar.addAction(cutAct)

        copyIcon = QIcon.fromTheme(QIcon.ThemeIcon.EditCopy,
                                   QIcon(":/demos/documentviewer/images/copy.png"))
        copyAct = QAction(copyIcon, "Copy", self)
        copyAct.setShortcuts(QKeySequence.Copy)
        copyAct.setStatusTip("Copy the current selection's contents to the clipboard")
        copyAct.triggered.connect(self._textEdit.copy)
        editMenu.addAction(copyAct)
        editToolBar.addAction(copyAct)

        pasteIcon = QIcon.fromTheme(QIcon.ThemeIcon.EditPaste,
                                    QIcon(":/demos/documentviewer/images/paste.png"))
        pasteAct = QAction(pasteIcon, "Paste", self)
        pasteAct.setShortcuts(QKeySequence.Paste)
        pasteAct.setStatusTip("Paste the clipboard's contents into the current selection")
        pasteAct.triggered.connect(self._textEdit.paste)
        editMenu.addAction(pasteAct)
        editToolBar.addAction(pasteAct)

        self.menuBar().addSeparator()

        cutAct.setEnabled(False)
        copyAct.setEnabled(False)
        self._textEdit.copyAvailable.connect(cutAct.setEnabled)
        self._textEdit.copyAvailable.connect(copyAct.setEnabled)

        self.openFile()

        self._textEdit.textChanged.connect(self._textChanged)
        self._uiAssets_back.triggered.connect(self._back)
        self._uiAssets_forward.triggered.connect(self._forward)

    @Slot()
    def _textChanged(self):
        self.maybeSetPrintingEnabled(self.hasContent())

    @Slot()
    def _back(self):
        bar = self._textEdit.verticalScrollBar()
        if bar.value() > bar.minimum():
            bar.setValue(bar.value() - 1)

    @Slot()
    def _forward(self):
        bar = self._textEdit.verticalScrollBar()
        if bar.value() < bar.maximum():
            bar.setValue(bar.value() + 1)

    def openFile(self):
        type = "open"
        file_name = QDir.toNativeSeparators(self._file.fileName())
        if not self._file.open(QFile.ReadOnly | QFile.Text):
            err = self._file.errorString()
            self.statusMessage(f"Cannot read file {file_name}:\n{err}.", type)
            return

        in_str = QTextStream(self._file)
        QGuiApplication.setOverrideCursor(Qt.WaitCursor)
        if self._textEdit.toPlainText():
            self._textEdit.clear()
            self.disablePrinting()

        self._textEdit.setPlainText(in_str.readAll())
        QGuiApplication.restoreOverrideCursor()

        self.statusMessage(f"File {file_name} loaded.", type)
        self.maybeEnablePrinting()

    def hasContent(self):
        return bool(self._textEdit.toPlainText())

    def printDocument(self, printer):
        if not self.hasContent():
            return

        self._textEdit.print_(printer)

    def saveFile(self, file):
        file_name = QDir.toNativeSeparators(self._file.fileName())
        errorMessage = ""
        QGuiApplication.setOverrideCursor(Qt.WaitCursor)
        if file.open(QFile.WriteOnly | QFile.Text):
            out = QTextStream(file)
            out << self._textEdit.toPlainText()
        else:
            error = file.errorString()
            errorMessage = f"Cannot open file {file_name} for writing:\n{error}."
        QGuiApplication.restoreOverrideCursor()

        if errorMessage:
            self.statusMessage(errorMessage)
            return False

        self.statusMessage(f"File {file_name} saved")
        return True

    def saveDocumentAs(self):
        dialog = QFileDialog(self.mainWindow())
        dialog.setWindowModality(Qt.WindowModal)
        dialog.setAcceptMode(QFileDialog.AcceptSave)
        if dialog.exec() != QDialog.Accepted:
            return False

        files = dialog.selectedFiles()
        self._file.setFileName(files[0])
        return self.saveDocument()

recentfilemenu.py

# Copyright (C) 2023 The Qt Company Ltd.
# SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause

from PySide6.QtWidgets import QMenu
from PySide6.QtCore import Signal, Slot


class RecentFileMenu(QMenu):
    fileOpened = Signal(str)

    def __init__(self, parent, recent):
        super().__init__(parent)
        self._recentFiles = recent
        self._recentFiles.changed.connect(self.updateList)
        self._recentFiles.destroyed.connect(self.deleteLater)
        self.updateList()

    @Slot()
    def updateList(self):
        for a in self.actions():
            del a

        if not self._recentFiles:
            self.addAction("<no recent files>")
            return

        for fileName in self._recentFiles.recentFiles():
            action = self.addAction(fileName)
            action.triggered.connect(self._emitFileOpened)

    @Slot()
    def _emitFileOpened(self):
        action = self.sender()
        self.fileOpened.emit(action.text())

recentfiles.py

# Copyright (C) 2023 The Qt Company Ltd.
# SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause

from enum import Enum, auto

from PySide6.QtCore import QFileInfo, QObject, QSettings, Signal, Slot


DEFAULT_MAX_FILES = 10


# Test if file exists and can be opened
def testFileAccess(fileName):
    return QFileInfo(fileName).isReadable()


class RemoveReason(Enum):
    Other = auto()
    Duplicate = auto()


class EmitPolicy(Enum):
    EmitWhenChanged = auto(),
    NeverEmit = auto()


s_maxFiles = "maxFiles"
s_openMode = "openMode"
s_fileNames = "fileNames"
s_file = "file"


class RecentFiles(QObject):

    countChanged = Signal(int)
    changed = Signal()

    def __init__(self, parent=None):
        super().__init__(parent)
        self._maxFiles = DEFAULT_MAX_FILES
        self._files = []

    # Access to QStringList member functions
    def recentFiles(self):
        return self._files

    def isEmpty(self):
        return not self._files

    # Properties
    def maxFiles(self):
        return self._maxFiles

    def setMaxFiles(self, maxFiles):
        self._maxFiles = maxFiles

    def addFile(self, fileName):
        self._addFile(fileName, EmitPolicy.EmitWhenChanged)

    def removeFile(self, fileName):
        idx = self._files.find(fileName)
        self._removeFile(idx, RemoveReason.Other)

    @Slot()
    def clear(self):
        if self.isEmpty():
            return
        self._files.clear()
        self.countChanged.emit(0)

    def _addFile(self, fileName, policy):
        if not testFileAccess(fileName):
            return

        # Remember size, as cleanup can result in a change without size change
        c = len(self._files)

        # Clean dangling and duplicate files
        i = 0
        while i < len(self._files):
            file = self._files[i]
            if not testFileAccess(file):
                self._removeFile(file, RemoveReason.Other)
            elif file == fileName:
                self._removeFile(file, RemoveReason.Duplicate)
            else:
                i += 1

        # Cut tail
        while len(self._files) > self._maxFiles:
            self.removeFile((len(self._files) - 1), RemoveReason.Other)

        self._files.insert(0, fileName)

        if policy == EmitPolicy.NeverEmit:
            return

        if policy == EmitPolicy.EmitWhenChanged:
            self.changed.emit()
            if c != len(self._files):
                self.countChanged.emit(len(self._files))

    @Slot(list)
    def addFiles(self, files):
        if files.isEmpty():
            return

        if len(files) == 1:
            self.addFile(files[0])
            return

        c = len(self._files)

        for file in files:
            self.addFile(file, EmitPolicy.NeverEmit)

        self.changed.emit()
        if len(self._files) != c:
            self.countChanged.emit(len(self._files))

    def _removeFile(self, p, reason):
        index = p
        if isinstance(p, str):
            index = self._files.index(p) if p in self._files else -1
        if index < 0 or index >= len(self._files):
            return
        del self._files[index]

        # No emit for duplicate removal, add emits changed later.
        if reason != RemoveReason.Duplicate:
            self.changed.emit()

    @Slot(QSettings, str)
    def saveSettings(self, settings, key):
        settings.beginGroup(key)
        settings.setValue(s_maxFiles, self.maxFiles())
        if self._files:
            settings.beginWriteArray(s_fileNames, len(self._files))
            for index, file in enumerate(self._files):
                settings.setArrayIndex(index)
                settings.setValue(s_file, file)
            settings.endArray()
        settings.endGroup()

    @Slot(QSettings, str)
    def restoreFromSettings(self, settings, key):
        settings.beginGroup(key)
        self.setMaxFiles(settings.value(s_maxFiles, DEFAULT_MAX_FILES, int))
        self._files.clear()  # clear list without emitting
        numberFiles = settings.beginReadArray(s_fileNames)
        for index in range(0, numberFiles):
            settings.setArrayIndex(index)
            absoluteFilePath = settings.value(s_file)
            self._addFile(absoluteFilePath, EmitPolicy.NeverEmit)
        settings.endArray()
        settings.endGroup()
        if self._files:
            self.changed.emit()
        return True

viewerfactory.py

The ViewerFactory class manages viewers for known file types. It loads all available viewers on construction and provides a public API to query the loaded plugins, their names, and supported MIME types.

# Copyright (C) 2023 The Qt Company Ltd.
# SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause

from enum import Enum, auto

from PySide6.QtWidgets import (QMessageBox)
from PySide6.QtCore import (QFileInfo, QMimeDatabase, QTimer)

from txtviewer.txtviewer import TxtViewer
from jsonviewer.jsonviewer import JsonViewer
from pdfviewer.pdfviewer import PdfViewer


class DefaultPolicy(Enum):
    NeverDefault = auto()
    DefaultToTxtViewer = auto()
    DefaultToCustomViewer = auto()


class ViewerFactory:

    def __init__(self, displayWidget, mainWindow,
                 policy=DefaultPolicy.NeverDefault):
        self._viewers = {}
        self._defaultViewer = None
        self._defaultWarning = True
        self._defaultPolicy = policy
        self._displayWidget = displayWidget
        self._mainWindow = mainWindow
        self._mimeTypes = []
        for v in [PdfViewer(), JsonViewer(), TxtViewer()]:
            self._viewers[v.viewerName()] = v
            if v.isDefaultViewer():
                self._defaultViewer = v

    def defaultPolicy(self):
        return self._defaultPolicy

    def setDefaultPolicy(self, policy):
        self._defaultPolicy = policy

    def defaultWarning(self):
        return self._defaultWarning

    def setDefaultWarning(self, on):
        self._defaultWarning = on

    def viewer(self, file):
        info = QFileInfo(file)
        db = QMimeDatabase()
        mimeType = db.mimeTypeForFile(info)

        viewer = self.viewerForMimeType(mimeType)
        if not viewer:
            print(f"Mime type {mimeType.name()} not supported.")
            return None

        viewer.init(file, self._displayWidget, self._mainWindow)
        return viewer

    def viewerNames(self, showDefault=False):
        if not showDefault:
            return self._viewers.keys()

        list = []
        for name, viewer in self._viewers.items():
            if ((self._defaultViewer and viewer.isDefaultViewer())
                    or (not self._defaultViewer and name == "TxtViewer")):
                name += "(default)"
            list.append(name)
        return list

    def viewers(self):
        return self._viewers.values()

    def findViewer(self, viewerName):
        for viewer in self.viewers():
            if viewer.viewerName() == viewerName:
                return viewer
        print(f"Plugin {viewerName} not loaded.")
        return None

    def viewerForMimeType(self, mimeType):
        for viewer in self.viewers():
            for type in viewer.supportedMimeTypes():
                if mimeType.inherits(type):
                    return viewer

        viewer = self.defaultViewer()

        if self._defaultWarning:
            mbox = QMessageBox()
            mbox.setIcon(QMessageBox.Warning)
            name = mimeType.name()
            viewer_name = viewer.viewerName()
            m = f"Mime type {name} not supported. Falling back to {viewer_name}."
            mbox.setText(m)
            mbox.setStandardButtons(QMessageBox.Ok)
            QTimer.singleShot(8000, mbox.close)
            mbox.exec()
        return viewer

    def defaultViewer(self):
        if self._defaultPolicy == DefaultPolicy.NeverDefault:
            return None
        if self._defaultPolicy == DefaultPolicy.DefaultToCustomViewer and self._defaultViewer:
            return self._defaultViewer
        return self.findViewer("TxtViewer")

    def supportedMimeTypes(self):
        if not self._mimeTypes:
            for viewer in self.viewers():
                self._mimeTypes.extend(viewer.supportedMimeTypes())
        return self._mimeTypes