How to use QTextFrame in QPlainTextEdit with QTextCursor?

My intention is to draw QTextFrame around the selected text in QPlainTextEdit.

This is what I have tried:

I can select the text but the frame is not drawn around it. Please guide.


mainwindow.cpp

Code:

---

#include "mainwindow.h"
#include<QFile>
#include<QLine>
#include<QTextDocument>
#include<QVBoxLayout>
 
MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
{
    setMouseTracking(true);
 
    objQPlainTextEdit.setPlainText("1234567890\n1234567890\n1234567890\n1234567890");
 
    connect(&objQPlainTextEdit, &QPlainTextEdit::cursorPositionChanged,
            [this]() {
                        extractTextBlock(objQPlainTextEdit.textCursor().selectedText());
                     }
           );
 
    QWidget     *objMainWidget = new QWidget( this );
    QVBoxLayout *objVBoxLayout = new QVBoxLayout( objMainWidget );
 
    objVBoxLayout->addWidget( &objQPlainTextEdit );
    objMainWidget->setLayout( objVBoxLayout );
 
    setCentralWidget( objMainWidget );
 
    objQTextFrame = new QTextFrame( objQPlainTextEdit.document()->rootFrame()->document() );
 
    objQTextCursor.select(QTextCursor::BlockUnderCursor);
    objQTextCursor = objQTextFrame->lastCursorPosition();
 
    objQTextFrameFormat.setBorder(11);
    objQPlainTextEdit.setTextCursor( objQTextCursor);
 
    objQColor.setRed(22);
    objQBrush.setColor( objQColor );
    objQTextFrameFormat.setBorderBrush( objQBrush );
 
    objQTextFrame->firstCursorPosition().insertFrame(objQTextFrameFormat);
}
 
MainWindow::~MainWindow(){}

---

mainwindow.h

Code:

---

#ifndef MAINWINDOW_H
#define MAINWINDOW_H
 
#include <QMainWindow>
#include <QTextCursor>
#include <QTextBlock>
#include <QPlainTextEdit>
#include <iostream>
#include <QDebug>
#include <QTextFrame>
#include <QBrush>
#include <QColor>
 
class MainWindow : public QMainWindow
{
    Q_OBJECT
 
public:
    QPlainTextEdit    objQPlainTextEdit;
    QTextFrame       *objQTextFrame;
    QTextFrameFormat  objQTextFrameFormat;
    QTextCursor       objQTextCursor;
    QBrush            objQBrush;
    QColor            objQColor;
 
    MainWindow( QWidget *parent = 0 );
    ~MainWindow();
 
public slots:
    void extractTextBlock( QString arg )
    {
        qDebug()<< "\n: " << arg << "\n";
    }
};

---