如何使用Qt5和QNetworkAccessManager下载文件

Question

I need a very simple console application to FTP into the server and get some file , I try with QNetworkAccessManager , and it seems like not working and getting nothing.

Here is my code ,

ftp.h

    #ifndef FTP_H
#define FTP_H
#include <string>
#include <vector>

#include <qstring.h>
#include <qfile.h>
#include <QNetworkAccessManager>
#include <QUrl>
#include <QNetworkRequest>
#include <QNetworkReply>
#include "qdebug.h"

#include <QCoreApplication>
#include <QDebug>
#include <string>
#include <iostream>
#include <sstream>
#include <QTextStream>
#include <QObject>

class ftp
{
//    Q_OBJECT
public:
    ftp();

private:
    QNetworkAccessManager *manager;
    QNetworkReply *reply;

private slots:
    void slotError(QNetworkReply::NetworkError code);
    void replyFinished(QNetworkReply *reply);
};

#endif // FTP_H

ftp.cpp

#include "ftp.h"
#include "QDebug"

#include <qstring.h>
#include <qfile.h>
#include <QNetworkAccessManager>
#include <QUrl>
#include <QNetworkRequest>
#include <QNetworkReply>
#include "qdebug.h"

#include <QCoreApplication>
#include <QDebug>
#include <string>
#include <iostream>
#include <sstream>
#include <QTextStream>
#include <QObject>

using namespace std;

ftp::ftp()
{
    qDebug() << "ZSS Server Program Running Now ...";

    QTextStream cin(stdin);
    QString username;
    QString password;
    QString ip;
    QString port;

    cout << "Username : ";
    username = cin.readLine();

    cout << "Password : ";
    password = cin.readLine();

    cout << "IP Address : ";
    ip = cin.readLine();

    cout << "Port Number : ";
    port = cin.readLine();

    QUrl url;
    url.setScheme("ftp");
    url.setHost("10.228.7.74");
    url.setPath("/try/hello.txt");
    url.setPort(21);
    url.setUserName("ftpTest");
    url.setPassword("ftpTest");
    QNetworkRequest request(url);
    //request.setUrl(url);

    qDebug() << url;

    //cout << "Downloading File...";

    manager = new QNetworkAccessManager;
    reply = manager->get(request);
    QByteArray buffer = reply->readAll();
    qDebug() << buffer;

//    connect(reply , SIGNAL(error(QNetworkReply::NetworkError)), this,SLOT(slotError(QNetworkReply::NetworkError)));
//    connect(manager, SIGNAL(finished(QNetworkReply*)),this,SLOT(replyFinished(QNetworkReply*)));
}

void ftp::slotError(QNetworkReply::NetworkError code)
{
    qDebug() << reply->errorString();
}

void ftp::replyFinished(QNetworkReply *reply)
{
//    QTextCodec *codec = QTextCodec::codecForName("utf8");
//    QString all = codectoUniCode(reply->readAll());
//    cout >> all;
//    reply->deleteLater();
}

After I run my code , inside my folder , I can't see any file is there. So I qDebug() out all the response and buffer , I found that the buffer and response is empty , is there any part I was missing or doing other things wrong ? Can I get a simple example for this ??

Here is the console output screenshots,

I qDebug() the buffer , but the buffer doesn't have anythings on it , I create this ftp local server by using 3CDaemon , and I was point to the correct folder and my ftp server is running , I can use command prompt to ftp inside and get the file , just can't make it by using Qt.

Please help me , this have been trouble me for couple of days..Thanks..

Answer 1

QNetworkAccessManager::get is an asynchronous function. You can use the QNetworkReply it returns to monitor the progress of the download, but isn't ready to read immediately. You have to wait until the finished signal is emitted (either by the QNetworkAccessManager or the QNetworkReply ) before you can read data from it.

If you really want the download to be synchronous, you can spin your own local event loop until the download finishes. For example

QEventLoop loop;
QNetworkAccessManager mgr;
connect(&mgr, &QNetworkAccessManager::finished, &loop, &QEventLoop::quit);

QNetworkReply *reply = mgr.get(...);
loop.exec();
qDebug() << reply.readAll();