【QT】基于HTTP协议的网络应用程序

void MainWindow::on_btnDefaultPath_clicked()
{//缺省路径  按钮
    QString  curPath=QDir::currentPath();
    QDir    dir(curPath);

    QString  sub="temp";
    dir.mkdir(sub);

    ui->editPath->setText(curPath+"/"+sub+"/");
}


void MainWindow::on_btnDownload_clicked()
{//开始下载 按钮
    QString urlSpec = ui->editURL->text().trimmed();
    if (urlSpec.isEmpty())
    {
        QMessageBox::information(this, "错误",
          "请指定需要下载的URL");
        return;
    }


    QUrl newUrl = QUrl::fromUserInput(urlSpec);//URL地址
    if (!newUrl.isValid())
    {
        QMessageBox::information(this, "错误",
          QString("无效URL: %1 \n 错误信息: %2").arg(urlSpec, newUrl.errorString()));
        return;
    }


    QString tempDir =ui->editPath->text().trimmed();//临时目录
    if (tempDir.isEmpty())
    {
        QMessageBox::information(this, tr("错误"), "请指定保存下载文件的目录");
        return;
    }


    QString fullFileName =tempDir+newUrl.fileName(); //文件名


    if (QFile::exists(fullFileName))
        QFile::remove(fullFileName);


    downloadedFile =new QFile(fullFileName);//创建临时文件
    if (!downloadedFile->open(QIODevice::WriteOnly))
    {
        QMessageBox::information(this, tr("错误"),"临时文件打开错误");
        return;
    }


    ui->btnDownload->setEnabled(false);

//发送网络请求，创建网络响应
    reply = networkManager.get(QNetworkRequest(newUrl));
    connect(reply, SIGNAL(finished()), this, SLOT(on_finished()));
    connect(reply, SIGNAL(readyRead()), this, SLOT(on_readyRead()));
    connect(reply, SIGNAL(downloadProgress(qint64,qint64)),
            this, SLOT(on_downloadProgress(qint64,qint64)));
}

代码在读取URL地址后，将其转换为一个QUrl类变量newUrl，并检查其有效性，再检查临时文件目录，创建临时文件downloadedFiIe。

这些准备好之后，用QNetworkAccessManager发布网络请求，请求下载URL地址表示的文件，并创建网络响应，关键代码为：

reply = networkManager.get(QNetworkRequest(newUrl));

        reply为网络响应，将其3个信号与相关的自定义槽函数相关联，实现相应的操作。这3个槽函数的代码如下：

void MainWindow::on_finished()
{//网络响应结束


//    QFileInfo fileInfo;
    if (downloadedFile) {
//        fileInfo.setFile(downloadedFile->fileName());
        downloadedFile->close();
        delete downloadedFile;
        downloadedFile = Q_NULLPTR;
    }


    QFileInfo fileInfo;
    fileInfo.setFile(downloadedFile->fileName());


    downloadedFile->close();
    delete downloadedFile;
    downloadedFile = Q_NULLPTR;


    reply->deleteLater(); //
    reply = Q_NULLPTR;


    if (ui->checkOpen->isChecked())//打开下载的文件
        QDesktopServices::openUrl(QUrl::fromLocalFile(fileInfo.absoluteFilePath()));


    ui->btnDownload->setEnabled(true);
}


void MainWindow::on_readyRead()
{//读取下载的数据
    downloadedFile->write(reply->readAll());
}


void MainWindow::on_downloadProgress(qint64 bytesRead, qint64 totalBytes)
{//下载进程
    ui->progressBar->setMaximum(totalBytes);
    ui->progressBar->setValue(bytesRead);
}