Qt网络请求下载图片并且显示

基本流程

• 字符串通过QUrl()变成Url对象，然后QNetworkRequest通过setUrl()方法设置URL，然后QNetworkManager通过get方法访问并且返回回复

QNetworkReply *newReply = netWorkManager->get(networkRequest);

• 回复对象具有downloadProgress(qint64, qint64)，readyRead()，finished()，三个信号，其中downloadProgress(qint64, qint64)用来更新进度条，readyRead()表示此时已经有数据可以读取（可能还没结束），finished()表示此时接收已经结束可以读到完整的文件

QByteArray data = reply->readAll();

• 上面是读取到回复的全文内容

更新进度条

void MainWindow::imageDownloadProgress(qint64 bytes, qint64 totalBytes)
{
    static qint8 count = 0;
    count++;
    if(count == 1)
        progressBar->setMaximum(totalBytes);

    progressBar->setValue(bytes);
}

下载结束显示图片

void MainWindow::replyFinished()
{
    //QNetworkReply *reply = (QNetworkReply *)sender();

    //reply->deleteLater();

    QNetworkReply *reply = (QNetworkReply *)sender();

    QByteArray data = reply->readAll();
    reply->deleteLater();

    if(data.isEmpty())
    {
        qDebug()<<"data is null, please try it again!"<<endl;
        return;
    }

    QPixmap pixmap;
    pixmap.loadFromData(data);

    label[0]->setPixmap(pixmap);

}

开始下载

void MainWindow::startDownload()
{
    QUrl newUrl(QUrl(lineEdit->text()));
    if(!newUrl.isValid())
    {
        QMessageBox::information(this, "error", "invalid url");
        return;
    }

    QNetworkRequest networkRequest;

    networkRequest.setUrl(newUrl);

    QNetworkReply *newReply = netWorkManager->get(networkRequest);

    connect(newReply, SIGNAL(finished()), this, SLOT(replyFinished()));
    connect(newReply, SIGNAL(readyRead()), this, SLOT(readyReadData()));
    connect(newReply, SIGNAL(downloadProgress(qint64, qint64)), this, SLOT(imageDownloadProgress(qint64, qint64)));
}