檔案得主要目錄如下圖：

再mainwindow.ui中只加了一個pushbutton

dialog.cpp中沒有任何操作 

最後付下主要程式碼：

#include "mainwindow.h"

#include "ui_mainwindow.h"

#include "ui_dialog.h"

#include <QFile>

#include <QFileDialog>

#include <QMessageBox>

#include <QDebug>

MainWindow::MainWindow(QWidget *parent) :

    QMainWindow(parent),

    ui(new Ui::MainWindow)

{

    ui->setupUi(this);

}

MainWindow::~MainWindow()

{

    delete ui;

}

void MainWindow::on_pushButton_clicked()

{

    QString fileFull, fileName, filePath,fileSuffix;
 

    QFileInfo fileinfo;

    fileFull = QFileDialog::getOpenFileName(this,tr("file"),"/",tr("text(*.txt)"));  //獲取整個檔名

    //fileFull = E:\QtCode\newExample\myTry\新建文字文件.txt

    //獲取檔案資訊

    fileinfo = QFileInfo(fileFull);

    //fileinfo = E:\QtCode\newExample\myTry\新建文字文件.txt

    //獲取檔名字

    fileName = fileinfo.fileName();

    //fileName = 新建文字文件.txt

    //獲取檔案字尾

    fileSuffix = fileinfo.suffix();

    //fileSuffix = txt

    //獲取檔案絕對路徑

    filePath = fileinfo.absolutePath();

    if(!fileFull.isNull())

    {

       QFile file(fileFull);

       if(!file.open(QFile::ReadOnly | QFile::Text))

        {

            QMessageBox::warning(this,tr("Error"),tr("read file error:&1").arg(file.errorString()));

            return;

        }

            QTextStream in(&file);

            QApplication::setOverrideCursor(Qt::WaitCursor);

            dialog = new Dialog(this);

            dialog->ui->lineEdit->setText(fileFull);

            dialog->ui->lineEdit_2->setText(fileName);

            dialog->ui->textEdit->setPlainText(in.readAll());

            QApplication::restoreOverrideCursor();

            dialog->show();

    }

    else

    {

       qDebug()<<"cancel";

    }

//            FileDialog::getOpenFileName(this,

//                                                                tr("Open File"),

//                                                                "/",

//                                                                tr("All Files (*.*)"));

//                QDesktopServices::openUrl(QUrl::fromLocalFile(QFileInfo(fileName).absoluteFilePath()));

}