如何从任何链接下载数据？ [英] How can I download data from any link?

问题描述

我想要在我的Qt程序中的以下链接上显示的字符串如何获得它？

http://en.wikipedia.org/w/api.php?action=opensearch&search=centaurus_constellation

我已编码以下文件，以获取字符串出现在m_DownloadedData上面的页面，但它在程序结束时存储空字符串，有人可以帮助我获取数据从上面的链接？

.h文件：

  #ifndef SKYOBJDESCRIPTION_H 
 #define SKYOBJDESCRIPTION_H 
 
 #include< QObject> 
 #include< QByteArray> 
 #include< QString> 
 #include< QNetworkAccessManager> 
 #include< QNetworkRequest> 
 #include< QNetworkReply> 
 
 class SkyObjDescription：public QObject 
 {
 Q_OBJECT 
 public：
 explicit SkyObjDescription（const QString soName，const QString soType，QObject * parent = 0） ; 
 
 virtual〜SkyObjDescription（）; 
 
 QByteArray downloadedData（）const; 
 
信号：
 void downloaded（）; 
 
私有插槽：
 
 void fileDownloaded（QNetworkReply * reply）; 
 
 private：
 QString soName，soType; 
 QByteArray m_DownloadedData; 
 
}; 
 
 #endif // SKYOBJDESCRIPTION_H 
  

和
.cpp档案

  #include< QString> 
 #include< QUrl> 
 #include< QDebug> 
 
 #includeskyobjdescription.h
 
 
 SkyObjDescription :: SkyObjDescription（const QString so_Name，const QString so_Type，QObject * parent）：soName（so_Name） soType（so_Type），QObject（parent）
 {
 QString wikiLink =http://en.wikipedia.org/w/api.php?action=opensearch&search=\"+ soName.replace ，_）。toLower（）+_+ soType.toLower（）+& format = xml& limit = 1.xml; 
 
 // QUrl wikiUrl（http://en.wikipedia.org/w/api.php?action=opensearch&search=hello_world&format=xml&limit=1.xml）; 
 m_DownloadedData = wikiUrl.toEncoded（）; 
 qDebug（）<< wikiUrl.toEncoded（）：< m_DownloadedData; 
 QNetworkRequest req（wikiUrl）; 
 
 QNetworkAccessManager * manager = new QNetworkAccessManager（this）; 
 connect（manager，SIGNAL（finished（QNetworkReply *）），SLOT（fileDownloaded（QNetworkReply *）））; 
 manager-> get（req）; 
 
} 
 
 SkyObjDescription ::〜SkyObjDescription（）
 {
 
} 
 
 void SkyObjDescription fileDownloaded（QNetworkReply * reply）
 {
 m_DownloadedData = reply-> readAll（）; 
 qDebug（）<< received reply; 
 qDebug（）<< m_DownloadedData; 
 reply-> deleteLater（）; 
 emit downloaded（）; 
} 
 
 QByteArray SkyObjDescription :: downloadedData（）const 
 {
 qDebug（）< m_DownloadedData; 
 return m_DownloadedData; 
} 
  

部分main.cpp

  SkyObjDescription * skd = new SkyObjDescription（m_Name，Constellation）; 
 QString data（skd-> downloadedData（））; 
 qDebug（）<<数据; 
 delete skd; 
  

如果有其他方式从链接获取数据，请解释。
非常感谢：）

解决方案

你可能试验的是你的双重呼叫 QNetworkReply :: readAll 。

记住它是一个IO操作，并且没有办法多次读取netwrk回复。

只需注释您的调试行：

  void SkyObjDescription :: fileDownloaded（QNetworkReply * pReply）
 {
 // qDebug（）<< pReply-> readAll（）; 
 m_DownloadedData = pReply-> readAll（）; 
 //发出一个信号
 pReply-> deleteLater（）; 
 emit downloaded（）; 
} 
  

编辑（完整性）

我使用的测试代码：

  #ifndef TMP_H 
 #define TMP_H 
 
 #include< QObject> 
 
 class QNetworkReply; 
 
 class Tmp：public QObject 
 {
 Q_OBJECT 
 public：
 explicit Tmp（QObject * parent = 0）; 
 
信号：
 
公共位置：
 void displayResult（QNetworkReply * reply）; 
 
}; 
 
 #endif // TMP_H 
 
 //tmp.cpp 
 #includetmp.h
 #include< QNetworkAccessManager> 
 #include< QNetworkReply> 
 #include< QNetworkRequest> 
 #include< QDebug> 
 
 Tmp :: Tmp（QObject * parent）：
 QObject（parent）
 {
 QUrl url（http://en.wikipedia.org/wiki / Centaurus_constellation）; 
 QNetworkRequest req（url）; 
 
 QNetworkAccessManager * manager = new QNetworkAccessManager（this）; 
 connect（manager，SIGNAL（finished（QNetworkReply *）），SLOT（displayResult（QNetworkReply *）））; 
 manager-> get（req）; 
} 
 
 void Tmp :: displayResult（QNetworkReply * reply）{
 QByteArray buffer = reply-> readAll（）; 
 qDebug（）<< received reply; 
 qDebug（）<<缓冲; 
 reply-> deleteLater（）; 
} 
  

I want to get string that appears on following link in my Qt program how can I get it ?

http://en.wikipedia.org/w/api.php?action=opensearch&search=centaurus_constellation

I have coded following files to get string appearing on above page in m_DownloadedData, but it is storing empty string at the end of the program , can someone please help me get data from above link ?

.h file:

#ifndef SKYOBJDESCRIPTION_H
#define SKYOBJDESCRIPTION_H

#include <QObject>
#include <QByteArray>
#include <QString>
#include <QNetworkAccessManager>
#include <QNetworkRequest>
#include <QNetworkReply>

class SkyObjDescription : public QObject
{
    Q_OBJECT
public:
    explicit SkyObjDescription(const QString soName, const QString soType, QObject* parent = 0);

    virtual ~SkyObjDescription();

    QByteArray downloadedData() const;

signals:
        void downloaded();

private slots:

    void fileDownloaded(QNetworkReply* reply);

private:
    QString soName,soType;
    QByteArray m_DownloadedData;

};

#endif // SKYOBJDESCRIPTION_H

and .cpp file

    #include <QString>
    #include <QUrl>
    #include <QDebug>

    #include "skyobjdescription.h"


    SkyObjDescription::SkyObjDescription(const QString so_Name, const QString so_Type, QObject* parent): soName(so_Name), soType(so_Type), QObject(parent)
    {
        QString wikiLink = "http://en.wikipedia.org/w/api.php?action=opensearch&search="+ soName.replace(" ", "_").toLower() + "_" + soType.toLower() + "&format=xml&limit=1.xml";

 //       QUrl wikiUrl("http://en.wikipedia.org/w/api.php?action=opensearch&search=hello_world&format=xml&limit=1.xml");
        m_DownloadedData = wikiUrl.toEncoded();
        qDebug() << "wikiUrl.toEncoded(): " << m_DownloadedData; 
        QNetworkRequest req(wikiUrl);

        QNetworkAccessManager* manager = new QNetworkAccessManager(this);
        connect(manager, SIGNAL(finished(QNetworkReply*)), SLOT(fileDownloaded(QNetworkReply*)));
        manager->get(req);

    }

    SkyObjDescription::~SkyObjDescription()
    {

    }

    void SkyObjDescription::fileDownloaded(QNetworkReply* reply)
    {
        m_DownloadedData = reply->readAll();
        qDebug() << "received reply";
        qDebug() << m_DownloadedData;
        reply->deleteLater();
        emit downloaded();
    }

    QByteArray SkyObjDescription::downloadedData() const
    {
        qDebug() << m_DownloadedData;
        return m_DownloadedData;
    }

part of main.cpp

SkyObjDescription * skd = new SkyObjDescription(m_Name, "Constellation");
        QString data(skd->downloadedData());
        qDebug() << data;
        delete skd;

If there is other way to get data from link please explain it. Thank you very much :)

解决方案

What you probably experiment is caused by your double call on QNetworkReply::readAll.

Remembers it is a IO operation, and there is no way to read multiple times the information contain by the netwrk reply.

Just comment your debug line :

void SkyObjDescription::fileDownloaded(QNetworkReply* pReply)
{
    //qDebug() << pReply->readAll();
    m_DownloadedData = pReply->readAll();
    //emit a signal
    pReply->deleteLater();
    emit downloaded();
}

edit (for completness)

The test code I use :

#ifndef TMP_H
#define TMP_H

#include <QObject>

class QNetworkReply;

class Tmp : public QObject
{
    Q_OBJECT
public:
    explicit Tmp(QObject *parent = 0);

signals:

public slots:
    void displayResult(QNetworkReply* reply);

};

#endif // TMP_H

//tmp.cpp
#include "tmp.h"
#include <QNetworkAccessManager>
#include <QNetworkReply>
#include <QNetworkRequest>
#include <QDebug>

Tmp::Tmp(QObject *parent) :
    QObject(parent)
{
    QUrl url("http://en.wikipedia.org/wiki/Centaurus_constellation");
    QNetworkRequest req(url);

    QNetworkAccessManager* manager = new QNetworkAccessManager(this);
    connect(manager, SIGNAL(finished(QNetworkReply*)), SLOT(displayResult(QNetworkReply*)));
    manager->get(req);
}

void Tmp::displayResult(QNetworkReply *reply) {
    QByteArray buffer = reply->readAll();
    qDebug() << "received reply";
    qDebug() << buffer;
    reply->deleteLater();
}

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