QT学习笔记-29.使用QT HTTP下载网络文件

 

QT附带的例子比较好:

class HttpWindow : public QDialog
{
    Q_OBJECT
public:
    HttpWindow(QWidget *parent = 0);

    void startRequest(QUrl url);
private slots:
    void downloadFile();
    void cancelDownload();
    void httpFinished();
    void httpReadyRead();
    void updateDataReadProgress(qint64 bytesRead, qint64 totalBytes);
    void enableDownloadButton();
    void slotAuthenticationRequired(QNetworkReply*,QAuthenticator *);
private:
    QLabel *statusLabel;
    QLabel *urlLabel;
    QLineEdit *urlLineEdit;
    QProgressDialog *progressDialog;
    QPushButton *downloadButton;
    QPushButton *quitButton;
    QDialogButtonBox *buttonBox;

    QUrl url;
    QNetworkAccessManager qnam;
    QNetworkReply *reply;
    QFile *file;
    int httpGetId;
    bool httpRequestAborted;
};

其中槽有:
1.开始下载
2.取消下载
3.预备下载
4.下载完成
5.进度回调
等

实现为:

void HttpWindow::startRequest(QUrl url)
{
    reply = qnam.get(QNetworkRequest(url));
    connect(reply, SIGNAL(finished()),
            this, SLOT(httpFinished()));
    connect(reply, SIGNAL(readyRead()),
            this, SLOT(httpReadyRead()));
    connect(reply, SIGNAL(downloadProgress(qint64,qint64)),
            this, SLOT(updateDataReadProgress(qint64,qint64)));
}

该函数主要针对给定url绑定事件

void HttpWindow::downloadFile()
{
    url = urlLineEdit->text();

    QFileInfo fileInfo(url.path());
    QString fileName = fileInfo.fileName();
    fileName = "downloadfile.dat";
    if(fileName.isEmpty())
        fileName = "index.html";

    if(QFile::exists(fileName)) {
        if (QMessageBox::question(this, tr("HTTP"), 
                                  tr("There already exists a file called %1 in "
                                     "the current directory. Overwrite?").arg(fileName),
                                  QMessageBox::Yes|QMessageBox::No, QMessageBox::No)
            == QMessageBox::No)
            return;
        QFile::remove(fileName);
    }

    file = new QFile(fileName);
    if (!file->open(QIODevice::WriteOnly)) {
        QMessageBox::information(this, tr("HTTP"),
                                 tr("Unable to save the file %1: %2.")
                                 .arg(fileName).arg(file->errorString()));
        delete file;
        file = 0;
        return;
    }

    progressDialog->setWindowTitle(tr("HTTP"));
    progressDialog->setLabelText(tr("Downloading %1.").arg(fileName));
    downloadButton->setEnabled(false);

    // schedule the request
    httpRequestAborted = false;
    startRequest(url);
}

当点击下载的时候，会执行该函数
获取url链接，生成本地文件，...

void HttpWindow::cancelDownload()
{
    statusLabel->setText(tr("Download canceled."));
    httpRequestAborted = true;
    reply->abort();
    downloadButton->setEnabled(true);
}

终止下载，主要函数是reply->abort();

void HttpWindow::httpFinished()
{
    if (httpRequestAborted) {
        if (file) {
            file->close();
            file->remove();
            delete file;
            file = 0;
        }
        reply->deleteLater();
        progressDialog->hide();
        return;
    }

    progressDialog->hide();
    file->flush();
    file->close();


    QVariant redirectionTarget = reply->attribute(QNetworkRequest::RedirectionTargetAttribute);
    if (reply->error()) {
        file->remove();
        QMessageBox::information(this, tr("HTTP"),
                                 tr("Download failed: %1.")
                                 .arg(reply->errorString()));
        downloadButton->setEnabled(true);
    } else if (!redirectionTarget.isNull()) {        
        QUrl newUrl = url.resolved(redirectionTarget.toUrl());
        if (QMessageBox::question(this, tr("HTTP"),
                                  tr("Redirect to %1 ?").arg(newUrl.toString()),
                                  QMessageBox::Yes | QMessageBox::No) == QMessageBox::Yes) {
            url = newUrl;
            reply->deleteLater();
            file->open(QIODevice::WriteOnly);
            file->resize(0);
            startRequest(url);
            return;
        }
    } else {
        QString fileName = QFileInfo(QUrl(urlLineEdit->text()).path()).fileName();
        statusLabel->setText(tr("Downloaded %1 to current directory.").arg(fileName));
        downloadButton->setEnabled(true);
    }

    reply->deleteLater();
    reply = 0;
    delete file;
    file = 0;
}

  下载结束动作

void HttpWindow::httpReadyRead()
{
    // this slot gets called every time the QNetworkReply has new data.
    // We read all of its new data and write it into the file.
    // That way we use less RAM than when reading it at the finished()
    // signal of the QNetworkReply
    if (file)
        file->write(reply->readAll());
}

写文件回调

void HttpWindow::updateDataReadProgress(qint64 bytesRead, qint64 totalBytes)
{
    if (httpRequestAborted)
        return;

    progressDialog->setMaximum(totalBytes);
    progressDialog->setValue(bytesRead);
}

进度回调

要点:
1.针对QNetReply绑定需要的信号和槽
2.实现需要的槽函数