QT实现，通过URL下载文件的接口实现

今天来把坑填上。 
具体就是提供一个URL，并通过这个URL下载文件。 
MyDownloader.h： 
#ifndef MYDOWNLOADER_H 
#define MYDOWNLOADER_H 
class MyDownloader :public QObject 
{ 
Q_OBJECT

public:

//构造函数，要求下载地址，保存位置，进度条（可选）
MyDownloader();
~MyDownloader();

// 设置要下载的url和文件名
void setData(QUrl url, QString pathtoSave);
//开始下载
void getFile();
void startRequest(QUrl url);
//发生的错误代码
int lastError();
//返回是否有错误发生
bool errorValid();
//返回是否下载中
bool isRunning();
//返回是否下载完成
bool isFinished();
//返回所下载文件的版本号
QString getDownloadVersionCode();
//返回所下载文件的名字（带扩展名）
QString getFileName();
void cancel();

private:

//=====状态变量=====
bool bisFinished;   //下载是否完成
bool bisRunning;    //下载是否进行中
bool bisError;      //是否有错误发生
int errorCode;      //错误代码
int allBits = 0;    //文件大小
bool httpRequestAborted;

//=====对象声明=====
QFile *downloadFile;                //保存目标文件指针
QUrl downloadUrl;                   //下载地址Url
QString savePath;                   //文件存放路径
QString versionCode = "";           //所下载的文件版本号
QString fileName = "";              //所下载文件名
QNetworkReply *downloadReply;       //网络应答指针
QNetworkAccessManager downloadmanager;     //网络连接主类指针

signals:

//当错误发生时向外抛出错误信息
void error(QNetworkReply::NetworkError);
//抛出下载进度(更新进度条)
void updateProgress(qint64, qint64);
//下载结果 0成功 其他失败
void downloadResult(int retCode);

private slots:

//准备下载，读取数据
void downloadReadyRead();
//下载完成
void downloadFinished();
//下载过程中发生错误
void downloadError(QNetworkReply::NetworkError);
//下载过程进度条
void downloadProgress(qint64, qint64);

};

#endif// MYDOWNLOADER_H

具体实现： 
MyDownloader.cpp：

MyDownloader::MyDownloader() 
{

downloadFile = NULL;
downloadReply = NULL;
bisFinished = false;

}

MyDownloader::~MyDownloader() 
{

cancel();

}

void MyDownloader::setData(QUrl url, QString pathtoSave) 
{

downloadUrl = url;
savePath = pathtoSave;

}

void MyDownloader::getFile() 
{

if (savePath.isEmpty() || downloadUrl.isEmpty())
{
    return;
}
if (downloadFile)
{
    return;
}
bisFinished = false;
downloadFile = new QFile(savePath);

if (!downloadFile->open(QIODevice::WriteOnly))
{
    delete downloadFile;
    downloadFile = 0;
    return;
}
allBits = downloadFile->size();
httpRequestAborted = false;
//尝试获取文件
startRequest(downloadUrl);
//事件循环，防止在下载没完成前结束对象

}

void MyDownloader::startRequest(QUrl url) 
{

QNetworkRequest req(url);
if (allBits)
{
    //QByteArray rangeHeaderValue = "bytes=" + QByteArray::number(allBits) + "-";// + QByteArray::number(already + cUpdateChunk() - 1);
    //req.setRawHeader("Range", rangeHeaderValue);
    //req.setAttribute(QNetworkRequest::HttpPipeliningAllowedAttribute, true);
    //req.setRawHeader("RANGE", tr("bytes=%1-").arg(allBits).toUtf8());//
}
downloadReply = downloadmanager.get(req);
//连接信号与槽
if (downloadReply)
{
    connect(downloadReply, SIGNAL(readyRead()), this, SLOT(downloadReadyRead()));
    connect(downloadReply, SIGNAL(finished()), this, SLOT(downloadFinished()));
    //connect(downloadReply, SIGNAL(error(QNetworkReply::NetworkError)), this, SLOT(downloadError(QNetworkReply::NetworkError)));
}

}

QString MyDownloader::getDownloadVersionCode() 
{

return versionCode;

}

QString MyDownloader::getFileName() 
{

return fileName;

}

void MyDownloader::downloadReadyRead() 
{

//如果文件可以访问，下载
if (downloadFile)
    downloadFile->write(downloadReply->readAll());

}

void MyDownloader::downloadProgress(qint64 bytesRead, qint64 totalBytes) 
{ 
}

void MyDownloader::cancel() 
{

if (downloadFile)
{
    downloadFile->close();
    delete downloadFile;
    downloadFile = NULL;
}
if (downloadReply)
{
    downloadReply->deleteLater();
    downloadReply = NULL;
}

}

void MyDownloader::downloadFinished() 
{

if (httpRequestAborted)
{
    cancel();
    return;
}
downloadFile->flush();
downloadFile->close();

QVariant redirectionTarget = downloadReply->attribute(QNetworkRequest::RedirectionTargetAttribute);
if (downloadReply->error())
{//299提示RANGE错误
    DEBUG_LOG(qsl("downloadReply error code:") + QString::number(downloadReply->error()));
    //downloadFile->remove();
    //emit downloadResult(-1);
}
else if (!redirectionTarget.isNull())
{
    QUrl newUrl = downloadUrl.resolved(redirectionTarget.toUrl());
    {
        downloadUrl = newUrl;
        downloadReply->deleteLater();
        downloadFile->open(QIODevice::WriteOnly);
        downloadFile->resize(0); allBits = 0;
        startRequest(downloadUrl);
        return;
    }
}
else
{
    QString fileName = QFileInfo(downloadUrl.path()).fileName();
    delete downloadFile;
    downloadFile = 0;
    bisFinished = true;
    emit downloadResult(0);
}
downloadReply->deleteLater();
downloadReply = 0;
if (downloadFile)
{
    delete downloadFile;
    downloadFile = 0;
}

}

void MyDownloader::downloadError(QNetworkReply::NetworkError errorcode) 
{

emit downloadResult(-1);

}

bool MyDownloader::errorValid() 
{

return false;

}

int MyDownloader::lastError() 
{

return 0;

}

bool MyDownloader::isRunning() 
{

return false;

}

bool MyDownloader::isFinished() 
{

return bisFinished;

} 
有些方法没有具体实现，（现在没有用到），是否有错误发生，判断是否下载中，是否下载完成，等 
////////////////////////////////////////////////////////////////////// 
使用： 
mian.cpp 
void main() 
{ 
MyDownloader m_downLoder; 
m_downLoder.setData(QUrl(m_si.custInfo.szLogoLargeUrl.c_str()), bigLogoPath); 
m_downLoder.cancel(); 
m_downLoder.getFile(); 
} 
////////////////////////////////////////////////////////////////////////////////////// 
全文完

http://blog.csdn.net/u011915578/article/details/46592963