Question

我正在尝试将工作代码集成到我的程序中，但是在编译时我收到了标题上显示的错误。这是代码：

/****************************************************************************
**
** Copyright (C) 2013 Digia Plc and/or its subsidiary(-ies).
** Contact: http://www.qt-project.org/legal
**
** This file is part of the examples of the Qt Toolkit.
**
****************************************************************************/

#include <QCoreApplication>
#include <QFile>
#include <QFileInfo>
#include <QList>
#include <QNetworkAccessManager>
#include <QNetworkRequest>
#include <QNetworkReply>
#include <QSslError>
#include <QStringList>
#include <QTimer>
#include <QUrl>

#include <stdio.h>

QT_BEGIN_NAMESPACE
class QSslError;
QT_END_NAMESPACE

QT_USE_NAMESPACE

class DownloadManager: public QObject
{
    Q_OBJECT
    QNetworkAccessManager manager;
    QList<QNetworkReply *> currentDownloads;

public:
    DownloadManager();
    ~DownloadManager() = 0;
    void doDownload(const QUrl &url);
    QString saveFileName(const QUrl &url);
    bool saveToDisk(const QString &filename, QIODevice *data);

public slots:
    void execute();
    void downloadFinished(QNetworkReply *reply);
    void sslErrors(const QList<QSslError> &errors);
};

DownloadManager::DownloadManager()
{
    connect(&manager, SIGNAL(finished(QNetworkReply*)),
            SLOT(downloadFinished(QNetworkReply*)));
}
DownloadManager::~DownloadManager()
{}

void DownloadManager::doDownload(const QUrl &url)
{
    QNetworkRequest request(url);
    QNetworkReply *reply = manager.get(request);

#ifndef QT_NO_SSL
    connect(reply, SIGNAL(sslErrors(QList<QSslError>)), SLOT(sslErrors(QList<QSslError>)));
#endif

    currentDownloads.append(reply);
}

QString DownloadManager::saveFileName(const QUrl &url)
{
    QString path = url.path();
    QString basename = QFileInfo(path).fileName();

    if (basename.isEmpty())
        basename = "download";

    if (QFile::exists(basename)) {
        // already exists, don't overwrite
        int i = 0;
        basename += '.';
        while (QFile::exists(basename + QString::number(i)))
            ++i;

        basename += QString::number(i);
    }

    return basename;
}

bool DownloadManager::saveToDisk(const QString &filename, QIODevice *data)
{
    QFile file(filename);
    if (!file.open(QIODevice::WriteOnly)) {
        fprintf(stderr, "Could not open %s for writing: %s\n",
                qPrintable(filename),
                qPrintable(file.errorString()));
        return false;
    }

    file.write(data->readAll());
    file.close();

    return true;
}

void DownloadManager::execute()
{
    QStringList args = QCoreApplication::instance()->arguments();
    args.takeFirst();           // skip the first argument, which is the program's name
    if (args.isEmpty()) {
        printf("Qt Download example - downloads all URLs in parallel\n"
               "Usage: download url1 [url2... urlN]\n"
               "\n"
               "Downloads the URLs passed in the command-line to the local directory\n"
               "If the target file already exists, a .0, .1, .2, etc. is appended to\n"
               "differentiate.\n");
        QCoreApplication::instance()->quit();
        return;
    }

    foreach (QString arg, args) {
        QUrl url = QUrl::fromEncoded(arg.toLocal8Bit());
        doDownload(url);
    }
}

void DownloadManager::sslErrors(const QList<QSslError> &sslErrors)
{
#ifndef QT_NO_SSL
    foreach (const QSslError &error, sslErrors)
        fprintf(stderr, "SSL error: %s\n", qPrintable(error.errorString()));
#else
    Q_UNUSED(sslErrors);
#endif
}

void DownloadManager::downloadFinished(QNetworkReply *reply)
{
    QUrl url = reply->url();
    if (reply->error()) {
        fprintf(stderr, "Download of %s failed: %s\n",
                url.toEncoded().constData(),
                qPrintable(reply->errorString()));
    } else {
        QString filename = saveFileName(url);
        if (saveToDisk(filename, reply))
            printf("Download of %s succeeded (saved to %s)\n",
                   url.toEncoded().constData(), qPrintable(filename));
    }

    currentDownloads.removeAll(reply);
    reply->deleteLater();

    if (currentDownloads.isEmpty())
        // all downloads finished
        QCoreApplication::instance()->quit();
}

//int main(int argc, char **argv)
//{
//    QCoreApplication app(argc, argv);

//    DownloadManager manager;
//    QTimer::singleShot(0, &manager, SLOT(execute()));

//    app.exec();
//}

//#include "main.moc"

在上面的代码中，我删除了main()（我将使用该类）和include "main.moc"（这会导致找不到错误）。我还添加了析构函数以防万一。

这是QtCreator中的项目文件：

QT += widgets core network

CONFIG += console
CONFIG -= app_bundle

SOURCES   = main.cpp \
    gos.cpp \
    download.cpp
HEADERS   = gos.h

QMAKE_PROJECT_NAME = GoS

# install
target.path = $$[QT_INSTALL_EXAMPLES]/widgets/tutorials/addressbook/part7
INSTALLS += target

simulator: warning(This example might not fully work on Simulator platform)

我错过了什么？

Answer 1

代码是头文件（.h）还是源文件（.cpp）？从QObject进行子类化时，moc取决于标题中的类定义。

将类定义从download.cpp拆分为download.h并将其添加到HEADERS变量中。请记住make distclean，然后再次调用qmake以获得干净的构建。

Answer 2

由于main.cpp文件包含Q_OBJECT宏，因此您需要在源文件的末尾生成main.moc个文件并#include "main.moc"。

实际上，qmake应该自行处理，但是在添加新的qmake行然后重新构建之后，您需要为项目重新运行#include。

未定义的对DownloadManager的vtable的引用

2 个答案: