如何使用 QNetworkAccessManager 作為 QT DLL function 下載文件？

Question

我正在嘗試創建一個 QT DLL 以在 InnoSetup 安裝程序中使用它（InnoSetup 是用 Delphi Pascal 編寫的）。

當從 InnoSetup 調用時，此 DLL 應該具有 function 以從 Internet 下載文件。

InnoSetup 調用是這樣進行的：

procedure downloadFile();
  external '_ZN9testClass10doDownloadEv@files:classTest.dll stdcall delayload';

然后我用這個來稱呼它：

function InitializeSetup(): Boolean;
begin
  Result := True;
  ExtractTemporaryFile('classTest.dll');
  downloadFile();
end;

我已經在我的 DLL 中嘗試了一個簡單的 function 並且它正在工作。 這里是測試 function：

extern "C" __declspec(dllexport) void testClass::testFunction()
{
    QFile file("output.txt");
    file.open(QIODevice::WriteOnly | QIODevice::Text);
    QTextStream out(&file);
    out << "Function call is working!";
    file.close();
}

現在，我嘗試在我的 DLL 中實現一個 function，它將使用 QNetworkAccessManager 和 QThreads 下載文件。 可悲的是，由於某種我無法理解的原因，這不起作用。

這是我的 DLL 代碼：

-- TESTDLL.H --

#ifndef TESTDLL_H
#define TESTDLL_H

#include <QtCore>

#include "testdll_global.h"
#include "libs/downloader.h"

class TESTCLASS_EXPORT testClass : public QObject
{
    Q_OBJECT
  public:
    void doDownload();
    void handleResults();
  public slots:
  private:
};

#endif // TESTDLL_H


-- TESTDLL_GLOBAL.H --

#ifndef TESTDLL_GLOBAL_H
#define TESTDLL_GLOBAL_H

#include <QtCore/qglobal.h>

#if defined(TESTCLASS_LIBRARY)
#  define TESTCLASS_EXPORT Q_DECL_EXPORT
#else
#  define TESTCLASS_EXPORT Q_DECL_IMPORT
#endif

#endif // TESTDLL_GLOBAL_H


-- TESTDLL.CPP --

#include "testdll.h"

extern "C" __declspec(dllexport) void testClass::doDownload()
{
     downloadWorker *ts_testDownloadWorker = new downloadWorker(this);
     connect(ts_testDownloadWorker, &downloadWorker::finished, ts_testDownloadWorker, &QObject::deleteLater);
     connect(ts_testDownloadWorker, &downloadWorker::resultReady, this, &testClass::handleResults);
     ts_testDownloadWorker->Execute();
}

void testClass::handleResults()
{
    QFile file("result.txt");
    file.open(QIODevice::WriteOnly | QIODevice::Text);
    QTextStream out(&file);
    out << "Passed!";
    file.close();
}


-- DOWNLOADER.H --

#ifndef DOWNLOADER_H
#define DOWNLOADER_H

#include <QtNetwork>
#include <QDebug>

class downloadWorker : public QThread
{
    Q_OBJECT
 signals:
    void resultReady(const QString &s);

 public:
    downloadWorker(QObject *parent);
    ~downloadWorker();
    void Execute();
    void saveToDisk(QString fileName, QByteArray content);

 protected:
    void run();

 private:
    bool m_abort;
    QNetworkAccessManager *networkMgr;
    QNetworkReply *replyNetworkSmall;

  public slots:
    void startDownload (QString url, QString fileName);
    QByteArray prepareDownload(QString &url);
    void downloadFinished(QNetworkReply *reply);
    void replyNetworkSmallError();
};

#endif // DOWNLOADER_H


-- DOWNLOADER.CPP --

#include "downloader.h"

downloadWorker::downloadWorker(QObject *parent)
    : QThread(parent)
{
    m_abort = false;
}

downloadWorker::~downloadWorker()
{
   m_abort = true;
   wait();
}

void downloadWorker::Execute()
{
    m_abort = false;
    start();
}

void downloadWorker::run()
{
    QString result;

    startDownload("http://www.google.com", "download.txt");
    exec();

    emit resultReady(result);
}

void downloadWorker::startDownload (QString url, QString fileName)
{
    QByteArray downloadUrl = prepareDownload(url);
    saveToDisk(fileName, downloadUrl);
}

QByteArray downloadWorker::prepareDownload(QString &url)
{
    QNetworkAccessManager *networkMgr = new QNetworkAccessManager;
    connect(networkMgr, SIGNAL(finished(QNetworkReply*)), this, SLOT(downloadFinished(QNetworkReply*)));

    QNetworkRequest request;
    request.setAttribute(QNetworkRequest::FollowRedirectsAttribute, true);
    request.setUrl(url);
    replyNetworkSmall = networkMgr->get(request);
    QEventLoop loop;
    connect(replyNetworkSmall, SIGNAL(finished()), &loop, SLOT(quit()));
    connect(replyNetworkSmall, SIGNAL(error(QNetworkReply::NetworkError)),
                this, SLOT(replyNetworkSmallError()));
    loop.exec();

    QByteArray bts = replyNetworkSmall->readAll();
    return bts;
}

void downloadWorker::saveToDisk(QString fileName, QByteArray content)
{
    QFile mfile(fileName);

    if (!mfile.open(QFile::ReadWrite))
        {
            mfile.close();
            QFile::remove(fileName);
        }
        else
        {
            mfile.write(content);
            mfile.flush();
            mfile.close();
        }
}

void downloadWorker::downloadFinished(QNetworkReply *reply)
{
    reply->deleteLater();
    this->exit();
}

void downloadWorker::replyNetworkSmallError()
{
    if(replyNetworkSmall->error())
    {
        //errorSmallDownload(replyNetworkSmall->errorString());
        //downloadError = true;
    }
    replyNetworkSmall->deleteLater();
}


-- TESTDLL.pro --

QT -= gui
QT += network

TEMPLATE = lib
DEFINES += TESTCLASS_LIBRARY

CONFIG += c++11 dll

# You can make your code fail to compile if it uses deprecated APIs.
# In order to do so, uncomment the following line.
# DEFINES += QT_DISABLE_DEPRECATED_BEFORE=0x060000    # disables all the APIs deprecated before Qt 6.0.0

SOURCES += \
    testdll.cpp \
    libs\downloader.cpp

HEADERS += \
    testdll_global.h \
    testdll.h \
    libs\downloader.h

QMAKE_LFLAGS += -Wl,--output-def,testdll.def

# Default rules for deployment.
unix {
    target.path = /usr/lib
}
!isEmpty(target.path): INSTALLS += target

如果我嘗試調用 doDownload function，沒有下載文件，就好像我的 dll 中沒有執行循環來實際完成這項工作。 但是，如果我將此代碼轉換為應用程序並使用帶有 exect 的 main，則文件正在下載。

我還能對上述代碼做些什么來實際管理下載文件？ 有什么我想念的嗎？

提前謝謝各位！

PS：我完全知道 InnoSetup 有他自己的文件下載器 function 實現。 但是，我想使用我自己的 DLL 下載的 function；）

解決方案

這是我的問題的解決方案，基於@MSalters 的回答：

-- TESTDLL.H --

#ifndef TESTDLL_H
#define TESTDLL_H

#include <QtCore>

#include "testdll_global.h"
#include "libs/downloader.h"

class testClass : public QObject
{
    Q_OBJECT
  public:
    void doDownload();
    void handleResults();
  public slots:
  private:
};

#endif // TESTDLL_H


-- TESTDLL.CPP --

#include "testdll.h"

namespace QCoreAppDLL
{
    static int argc = 1;
    static char * argv[] = {(char *)"testdll.cpp", nullptr};
    static QCoreApplication * pApp = nullptr;
}

extern "C" TESTCLASS_EXPORT void initDLL()
{
    if (!QCoreApplication::instance())
    {
        QCoreAppDLL::pApp = new QCoreApplication(QCoreAppDLL::argc, QCoreAppDLL::argv);

        testClass w;
        w.doDownload();

        QCoreAppDLL::pApp->exec();
    }
}

void testClass::doDownload()
{
     downloadWorker *ts_testDownloadWorker = new downloadWorker(this);
     connect(ts_testDownloadWorker, &downloadWorker::finished, ts_testDownloadWorker, &QObject::deleteLater);
     connect(ts_testDownloadWorker, &downloadWorker::resultReady, this, &testClass::handleResults);
     ts_testDownloadWorker->Execute();
}

void testClass::handleResults()
{
    if (QCoreAppDLL::pApp)
        QCoreAppDLL::pApp->quit();
}

Answer 1

如您所述，在普通的 Qt 應用程序中，這將起作用。 那是因為您的QApplication object 處理QCoreApplication::notify function。 在您的 DLL 中，您不需要完整的QApplication但您仍然需要至少一個QCoreApplication