Qt 网络编程2 下载一个网络文件

 实现功能：输入资源地址，点击下载，下载该文件，并显示下载进度。

代码如下：

myHttp2.pro

QT       += network

 mainwindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include <QUrl>

namespace Ui {
class MainWindow;
}

class QFile;
class QNetworkReply;
class QNetworkAccessManager;
class MainWindow : public QMainWindow
{
    Q_OBJECT

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

    void startRequest(QUrl url);
private:
    Ui::MainWindow *ui;

    QNetworkAccessManager* manager;
    QNetworkReply *reply;
    QUrl url;
    QFile *file;
private slots:
    void httpFinished();
    void httpReadyRead();
    void updateDataReadProgress(qint64,qint64);
    void on_pushButton_clicked();
};

#endif // MAINWINDOW_H

mainwindow.cpp

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QtNetwork>
#include <QFile>
#include <QDebug>
MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);

    manager = new QNetworkAccessManager(this);
    ui->progressBar->hide();
}

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

void MainWindow::startRequest(QUrl url)
{
    reply = manager->get(QNetworkRequest(url));
    connect(reply,&QNetworkReply::readyRead,this,&MainWindow::httpReadyRead);
    connect(reply,&QNetworkReply::downloadProgress,this,&MainWindow::updateDataReadProgress);
    connect(reply,&QNetworkReply::finished,this,&MainWindow::httpFinished);
}

void MainWindow::httpReadyRead()
{
    if (file) {
        file->write(reply->readAll());
    }
}

void MainWindow::updateDataReadProgress(qint64 bytesRead,qint64 totalBytes)
{
    ui->progressBar->setMaximum(totalBytes);
    ui->progressBar->setValue(bytesRead);
}

void MainWindow::httpFinished()
{
    ui->progressBar->hide();
    if (file) {
        file->close();
        delete file;
        file = nullptr;
    }
    reply->deleteLater();
    reply = 0;
}

void MainWindow::on_pushButton_clicked()
{
    url = ui->lineEdit->text();
    QFileInfo info(url.path());
    QString fileName(info.fileName());
    qDebug()<<fileName;
    if (fileName.isEmpty()) {
        fileName = "index.html";
    }
    file = new QFile(fileName);
    if (!file->open(QIODevice::WriteOnly)) {
        delete file;
        file = 0;
        return;
    }
    startRequest(url);
    ui->progressBar->setValue(0);
    ui->progressBar->show();
}

这里使用了get(）函数来发送网络请求，然后进行了 QNetworkReply对象的几个信号和自定义槽的关联。其中readyRead()信号继承自QIODevice类，每当有新的数据可以读取时，都会发射该信号；每当网络请求的下载进度更新时都会发射download-progress()信号，用来更新进度条；每当应答处理结束时都会发射finished()信号，该信号与前面程序中QNetworAccessManager类的finished()信号作用相同，只不过发送者不同，参数也不同而已。