QT 打开文件并且显示文件内容 （QFileDialog QMessageBox QTextStream ）

QFile
QTextStream
QMessageBox
QFileDialog
应用示例
mainwindow.cpp
#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QFile>
#include <QTextStream>
#include <QMessageBox>
#include <QFileDialog>
MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
    , ui(new Ui::MainWindow)
{
    ui->setupUi(this);
}

MainWindow::~MainWindow()
{
    delete ui;
}

mainwindow.cpp
void MainWindow::on_pushButton_2_clicked()
{
    //QFile file("./mytest1.txt");
    QFile file("/mnt/hgfs/temp/QFileDemo/mytext.txt");
    if(!file.open(QFile::WriteOnly | QFile::Text)){
        QMessageBox::warning(this,"title","file not open");
    }
    QTextStream out(&file);
    QString text= ui->plainTextEdit->toPlainText();
    out<<text;
    file.flush();
    file.close();
}

void MainWindow::on_pushButton_clicked()
{    QString filter="All File(*.*);;Text File(*.txt);;xml File(*.xml)";
    QString file_name=QFileDialog::getOpenFileName(this,"open a file","/",filter);
    QFile file(file_name);
    //QFile file("/mnt/hgfs/temp/QFileDemo/mytext.txt");
    if(!file.open(QFile::ReadOnly | QFile::Text)){
        QMessageBox::warning(this,"title","file not open");
    }
    QTextStream in(&file);
    QString text=in.readAll();
    ui->plainTextEdit->setPlainText(text);
    file.close();
}
mainwindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>

QT_BEGIN_NAMESPACE
namespace Ui { class MainWindow; }
QT_END_NAMESPACE

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    MainWindow(QWidget *parent = nullptr);
    ~MainWindow();

private slots:
    void on_pushButton_2_clicked();

    void on_pushButton_clicked();

private:
    Ui::MainWindow *ui;
};
#endif // MAINWINDOW_H