QT学习总结--断点下载
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想要利用qt完成断点下载需要了解一下http请求的Range字段。 Range字段的作用是支持http协议的范围请求，用法如下：
Range:bytes=1-99 表示下载1到99字节
Range:bytes=100- 表示下载100字节之后的所有字节
另外，qt提供了downloadProgress信号（qint64 ,qin64）来提供下载进度的反馈，第一个参数为收到的字节数，第二个为总字节数，两者都是指的一次请求的接收字节数和总字节数（如：Range:bytes=100-199 这次请求总字节数为100）
效果：
在下载链接中添加地址，点击start按钮开始或继续下载，点击stop按钮停止，点击close关闭下载，删除临时文件。在下载完成前，以临时文件的形式存在，完成后改为下载的文件格式，在暂停下载后，保存已下载的字节，作为下次下载的起点。
主要的功能类为DownLoadManager，主要有下载，停止，进度通知，完成功能。
利用downloadProgress，finished，readyread信号与功能关联。
代码如下：
downloadmanager.cpp
#include "downloadmanager.h"
#include <QFile>
#include <QDebug>
#include <QFileInfo>
#include <QMessageBox>
#define DOWNLOAD_FILE_SUFFIX "_tmp"
DownLoadManager::DownLoadManager(QObject *parent)
: QObject(parent)
{
m_networkManager = new QNetworkAccessManager(this);
}
DownLoadManager::~DownLoadManager()
{}
// 设置是否支持断点续传;
void DownLoadManager::setDownInto(bool isSupportBreakPoint)
{
m_isSupportBreakPoint = isSupportBreakPoint;
}
// 获取当前下载链接;
QString DownLoadManager::getDownloadUrl()
{
return m_url.toString();
}
// 开始下载文件，传入下载链接和文件的路径;
void DownLoadManager::downloadFile(QString url , QString fileName)
{
// 防止多次点击开始下载按钮，进行多次下载，只有在停止标志变量为true时才进行下载;
if (m_isStop)
{
m_isStop = false;
m_url = QUrl(url);
// 将当前文件名设置为临时文件名，下载完成时修改回来;
m_fileName = fileName + DOWNLOAD_FILE_SUFFIX;
// 如果当前下载的字节数为0那么说明未下载过或者重新下载
// 则需要检测本地是否存在之前下载的临时文件，如果有则删除
if (m_bytesCurrentReceived <= 0)
{
removeFile(m_fileName);
}
QNetworkRequest request;
request.setUrl(m_url);
// 如果支持断点续传，则设置请求头信息
if (m_isSupportBreakPoint)
{
QString strRange = QString("bytes=%1-").arg(m_bytesCurrentReceived);
request.setRawHeader("Range", strRange.toLatin1());
}
// 请求下载;
m_reply = m_networkManager->get(request);
connect(m_reply, SIGNAL(downloadProgress(qint64, qint64)), this, SLOT(onDownloadProgress(qint64, qint64)));
connect(m_reply, SIGNAL(readyRead()), this, SLOT(onReadyRead()));
connect(m_reply, SIGNAL(finished()), this, SLOT(onFinished()));
connect(m_reply, SIGNAL(error(QNetworkReply::NetworkError)), this, SLOT(onError(QNetworkReply::NetworkError)));
}
}
// 下载进度信息;
void DownLoadManager::onDownloadProgress(qint64 bytesReceived, qint64 bytesTotal)
{
if (!m_isStop)
{
m_bytesReceived = bytesReceived;
m_bytesTotal = bytesTotal;
// 更新下载进度;(加上 m_bytesCurrentReceived 是为了断点续传时之前下载的字节)
emit signalDownloadProcess(m_bytesReceived + m_bytesCurrentReceived, m_bytesTotal + m_bytesCurrentReceived);
}
}
// 获取下载内容，保存到文件中;
void DownLoadManager::onReadyRead()
{
if (!m_isStop)
{
QFile file(m_fileName);
if (file.open(QIODevice::WriteOnly | QIODevice::Append))
{
file.write(m_reply->readAll());
}
file.close();
}
}
// 下载完成;
void DownLoadManager::onFinished()
{
m_isStop = true;
// http请求状态码;
QVariant statusCode = m_reply->attribute(QNetworkRequest::HttpStatusCodeAttribute);
if (m_reply->error() == QNetworkReply::NoError)
{
// 重命名临时文件;
QFileInfo fileInfo(m_fileName);
if (fileInfo.exists())
{
int index = m_fileName.lastIndexOf(DOWNLOAD_FILE_SUFFIX);
QString realName = m_fileName.left(index);
QFile::rename(m_fileName, realName);
}
}
else
{
// 有错误输出错误;
QString strError = m_reply->errorString();
qDebug() << "__________" + strError;
}
emit signalReplyFinished(statusCode.toInt());
}
// 下载过程中出现错误，关闭下载，并上报错误，这里未上报错误类型，可自己定义进行上报;
void DownLoadManager::onError(QNetworkReply::NetworkError code)
{
QString strError = m_reply->errorString();
qDebug() << "__________" + strError;
closeDownload();
QMessageBox::information(NULL, "警告","出现错误！");
}
// 停止下载工作;
void DownLoadManager::stopWork()
{
m_isStop = true;
if (m_reply != NULL)
{
disconnect(m_reply, SIGNAL(downloadProgress(qint64, qint64)), this, SLOT(onDownloadProgress(qint64, qint64)));
disconnect(m_reply, SIGNAL(readyRead()), this, SLOT(onReadyRead()));
disconnect(m_reply, SIGNAL(finished()), this, SLOT(onFinished()));
disconnect(m_reply, SIGNAL(error(QNetworkReply::NetworkError)), this, SLOT(onError(QNetworkReply::NetworkError)));
m_reply->abort();
m_reply->deleteLater();
m_reply = NULL;
}
}
// 暂停下载按钮被按下,暂停当前下载;
void DownLoadManager::stopDownload()
{
// 这里m_isStop变量为了保护多次点击暂停下载按钮，导致m_bytesCurrentReceived 被不停累加;
if (!m_isStop)
{
//记录当前已经下载字节数
m_bytesCurrentReceived += m_bytesReceived;
stopWork();
}
}
// 重置参数;
void DownLoadManager::reset()
{
m_bytesCurrentReceived = 0;
m_bytesReceived = 0;
m_bytesTotal = 0;
}
// 删除文件;
void DownLoadManager::removeFile(QString fileName)
{
// 删除已下载的临时文件;
QFileInfo fileInfo(fileName);
if (fileInfo.exists())
{
QFile::remove(fileName);
}
}
// 停止下载按钮被按下，关闭下载，重置参数，并删除下载的临时文件;
void DownLoadManager::closeDownload()
{
stopWork();
reset();
removeFile(m_fileName);
}
mainwindow.cpp
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this);
initWindow();
}
MainWindow::~MainWindow()
{
}
void MainWindow::initWindow()
{
ui->progressBar->setValue(0);
connect(ui->pButtonStart, SIGNAL(clicked()), this, SLOT(onStartDownload()));
connect(ui->pButtonStop, SIGNAL(clicked()), this, SLOT(onStopDownload()));
connect(ui->pButtonClose, SIGNAL(clicked()), this, SLOT(onCloseDownload()));
}
// 开始下载;
void MainWindow::onStartDownload()
{
// 从界面获取下载链接;
m_url = ui->downloadUrl->text();
if (m_downloadManager == NULL)
{
m_downloadManager = new DownLoadManager(this);
connect(m_downloadManager , SIGNAL(signalDownloadProcess(qint64, qint64)), this, SLOT(onDownloadProcess(qint64, qint64)));
connect(m_downloadManager, SIGNAL(signalReplyFinished(int)), this, SLOT(onReplyFinished(int)));
}
// 这里先获取到m_downloadManager中的url与当前的m_url 对比，如果url变了需要重置参数,防止文件下载不全;
QString url = m_downloadManager->getDownloadUrl();
if (url != m_url)
{
m_downloadManager->reset();
}
m_downloadManager->setDownInto(true);
QString savePath = "H:/test/";
savePath += m_url.mid(m_url.lastIndexOf("/")+1, (m_url.lastIndexOf("?")>0 ? m_url.lastIndexOf("?") : m_url.length()) - m_url.lastIndexOf("/"));
m_downloadManager->downloadFile(m_url, savePath);
m_timeRecord.start();
m_timeInterval = 0;
ui->labelStatus->setText(QStringLiteral("正在下载"));
}
// 暂停下载;
void MainWindow::onStopDownload()
{
ui->labelStatus->setText(QStringLiteral("停止下载"));
if (m_downloadManager != NULL)
{
m_downloadManager->stopDownload();
}
}
// 关闭下载;
void MainWindow::onCloseDownload()
{
m_downloadManager->closeDownload();
ui->progressBar->setValue(0);
ui->labelStatus->setText(QStringLiteral("关闭下载"));
}
// 更新下载进度条;
void MainWindow::onDownloadProcess(qint64 bytesReceived, qint64 bytesTotal)
{
// 输出当前下载进度;
qDebug() << QString("%1").arg(bytesReceived * 100 / (bytesTotal+1));
// 更新进度条;
ui->progressBar->setMaximum(bytesTotal);
ui->progressBar->setValue(bytesReceived);
}
// 下载完成;
void MainWindow::onReplyFinished(int statusCode)
{
// 根据状态码判断当前下载是否出错;
if (statusCode >= 200 && statusCode < 400)
{
qDebug() << "Download Success";
}
else
{
qDebug() << "Download Failed";
}
}
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