Here's the full code:

mainwindow.h
Qt Code: 
  1. #ifndef MAINWINDOW_H
  2. #define MAINWINDOW_H
  3.  
  4. #include <QMainWindow>
  5. #include <QTextBrowser>
  6. #include <QPushButton>
  7. #include <QMouseEvent>
  8. #include <QTextCursor>
  9. #include <QTextDocumentFragment>
  10.  
  11. QT_BEGIN_NAMESPACE
  12. namespace Ui { class MainWindow; }
  13. QT_END_NAMESPACE
  14.  
  15. class MainWindow : public QMainWindow
  16. {
  17.     Q_OBJECT
  18.  
  19. public:
  20.     explicit MainWindow(QWidget *parent = nullptr);
  21.     ~MainWindow();
  22.  
  23. private slots:
  24.     void handleInsert();
  25.     void handleSelect();
  26. private:
  27.     Ui::MainWindow *ui;
  28.  
  29.     QPushButton *ButtonInsert;
  30.     QTextBrowser *ListWindow;
  31. };
  32.  
  33. #endif // MAINWINDOW_H
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main.cpp
Qt Code: 
  1. #include "mainwindow.h"
  2.  
  3. #include <QApplication>
  4.  
  5. int main(int argc, char *argv[])
  6. {
  7.     QApplication a(argc, argv);
  8.  
  9.     MainWindow w;
  10.     w.show();
  11.     return a.exec();
  12. }
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mainwindow.cpp
Qt Code: 
  1. #include "mainwindow.h"
  2. #include "ui_mainwindow.h"
  3.  
  4. MainWindow::MainWindow(QWidget *parent)
  5.     : QMainWindow(parent)
  6.     , ui(new Ui::MainWindow)
  7. {
  8.     ui->setupUi(this);
  9.     ButtonInsert = new QPushButton("Insert", this);
  10.     ButtonInsert -> setGeometry(QRect(QPoint(440,90), QSize(100,30)));
  11.  
  12.     ListWindow = new QTextBrowser(this);
  13.     ListWindow -> setGeometry(QRect(QPoint(50,50), QSize(300,500)));
  14.     ListWindow -> setText("This is a test");
  15.  
  16.     connect(ListWindow, &QTextBrowser::cursorPositionChanged, this, &MainWindow::handleSelect);
  17.     connect(ButtonInsert, &QPushButton::released, this, &MainWindow::handleInsert);
  18. }
  19.  
  20. MainWindow::~MainWindow()
  21. {
  22.     delete ui;
  23. }
  24.  
  25. void MainWindow::handleInsert(){
  26.     //test code for learning
  27.     ButtonInsert->setText("Inserting...");
  28.     ButtonInsert->setText("Inserted");
  29. }
  30.  
  31. void MainWindow::handleSelect(){
  32.     ListWindow->moveCursor(QTextCursor::StartOfLine);
  33.     ListWindow->moveCursor(QTextCursor::EndOfLine, QTextCursor::KeepAnchor);
  34. }
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