C++错误:没有使用Qt和QVariant从指针到指针引用的匹配函数调用

Question

我有一个这样定义的QObject子类（在"Danbooru"命名空间内）：

#ifndef DANBOORUPOST_H
#define DANBOORUPOST_H
// Qt
#include <QtCore/QObject>
#include <QtCore/QVariant>
#include <QtCore/QStringList>
#include <QtXml/QXmlStreamAttributes>
// KDE
#include <kurl.h>

class QPixmap;
namespace Danbooru {
    class DanbooruPost : public QObject
    {
    Q_OBJECT
    Q_PROPERTY(QPixmap* pixmap READ pixmap WRITE setPixmap)
    Q_PROPERTY(int id READ id)
    Q_PROPERTY(KUrl fileUrl READ fileUrl)
    Q_PROPERTY(QStringList tags READ tags)
    Q_PROPERTY(KUrl thumbnailUrl READ thumbnailUrl)
    private:
        QPixmap* m_pixmap;
        // basic features of a post
        int m_id;
        int m_height;
        int m_width;
        int m_size;
        KUrl m_url;
        KUrl m_thumbnailUrl;
        QStringList m_tags;
    public:
        explicit DanbooruPost(QVariantMap postData, QPixmap* pixmap = 0,
                              QObject* parent = 0);
        explicit DanbooruPost(QXmlStreamAttributes& postData,
                              QPixmap* pixmap = 0,  QObject* parent=0);
        bool operator==(const DanbooruPost&);
        ~DanbooruPost();
        // Post attributes
        int id() const;
        int height() const;
        int width() const;
        int size() const;
        const KUrl fileUrl() const;
        QStringList tags() const;
        const KUrl thumbnailUrl() const;
        QPixmap* pixmap() const;
        void setPixmap(QPixmap* pixmap);
        const QString toString();
    };
}; // namespace Danbooru
Q_DECLARE_METATYPE(Danbooru::DanbooruPost*)
#endif // DANBOORUPOST_H

我在另一个定义如下的类中使用它：

#ifndef DANBOORUSERVICE_H
#define DANBOORUSERVICE_H
#include <QtCore/QObject>
#include <QtCore/QString>
#include <QtCore/QStringList>
#include <KUrl>
#include <KIO/JobClasses>
class QPixmap;
class KUrl;
class KJob;
class DanbooruPost;
namespace Danbooru {
    enum TagType {
        General,
        Artist,
        Copyright,
        Character
    };
    using KIO::StoredTransferJob;
    class DanbooruService : public QObject
    {
    Q_OBJECT
    private:
        // URL fragments
        static const QString POST_URL;
        static const QString TAG_URL;
        static const QString POOL_URL;
        static const QString ARTIST_URL;
        static const QString POOL_DATA_URL;
        static const QString RELATED_TAG_URL;
        // member variables
        KUrl m_url;
        QString m_username;
        QString m_password;
        QStringList m_blacklist;
        QString m_maxRating;

    public:
        DanbooruService(KUrl& boardUrl, QString username = QString(),
                        QString password = QString(),
                        QStringList blacklist = QStringList(),
                        QObject* parent=0);
        ~DanbooruService();
        void getPostList(int page=1, QStringList tags=QStringList(),
                        int limit=100, QString rating="Safe");
        void getPoolList(int page=0);
        void getPool(int poolId, int page=1, QString rating="Safe");
        void getTagList(int limit=10, QString name="");
        void getRelatedTags(QStringList tags=QStringList(),
                            TagType tag_type=General);
        QString allowedRating() const;
        QStringList blacklist() const;

    private Q_SLOTS:
        void processPostList(StoredTransferJob* job);
        void processPoolList(StoredTransferJob* job);
        void processRelatedTagList(StoredTransferJob* job);
        void downloadThumbnail(StoredTransferJob* job);
        void downloadAllTags(StoredTransferJob* job);
    Q_SIGNALS:
        void postDownloadFinished();
        void poolDownloadFinished();
        void downloadError(QString error);
        void postDownloaded(DanbooruPost*&post);
        void postMetadataDownloaded(DanbooruPost* post);
        // TODO: Tags and similar
    };
};

我遇到的问题源于以下代码（StoredTransferJob是一个KDE类）：

void DanbooruService::downloadThumbnail(StoredTransferJob* job)
    {
        if (job->error()) {
            Q_EMIT(downloadError(job->errorString()));
        }
        QVariant postData = job->property("danbooruPost");
        DanbooruPost* post = (DanbooruPost*) postData.data();
        QPixmap* pix = new QPixmap();
        bool ok = pix->loadFromData(job->data());
        if (!ok) {
            Q_EMIT(downloadError(QString("Pixmap data could not be loaded")));
        }
        post->setPixmap(pix);
        Q_EMIT(postDownloaded(post));
    }

然而，在编译时，Q_EMIT部分会生成以下错误：

/home/lb/Coding/cpp/danbooru_client/src/libdanbooru/danbooruservice.cpp: In member function ‘void Danbooru::DanbooruService::downloadThumbnail(KIO::StoredTransferJob*)’:
/home/lb/Coding/cpp/danbooru_client/src/libdanbooru/danbooruservice.cpp:186:35: error: no matching function for call to ‘Danbooru::DanbooruService::postDownloaded(Danbooru::DanbooruPost*&)’
/home/lb/Coding/cpp/danbooru_client/src/libdanbooru/danbooruservice.cpp:186:35: note: candidate is:
In file included from /home/lb/Coding/cpp/danbooru_client/src/libdanbooru/danbooruservice.cpp:30:0:
/home/lb/Coding/cpp/danbooru_client/src/libdanbooru/danbooruservice.h:104:14: note: void Danbooru::DanbooruService::postDownloaded(DanbooruPost*&)
/home/lb/Coding/cpp/danbooru_client/src/libdanbooru/danbooruservice.h:104:14: note:   no known conversion for argument 1 from ‘Danbooru::DanbooruPost*’ to ‘DanbooruPost*&’

生成函数中使用的变体的代码是：

void DanbooruService::processPostList(KIO::StoredTransferJob* job)
{
    qDebug() << "Got data OK";
    if (job->error()) {
        Q_EMIT(downloadError(job->errorString()));
    }
    QByteArray data = job->data();
    QJson::Parser parser;
    bool ok;
    QVariant result = parser.parse(data, &ok);
    if (!ok) {
        Q_EMIT(downloadError(QString("Unable to decode data")));
    }
    QList<QVariant> postList = result.toList();
    Q_FOREACH(QVariant element, postList) {
        QVariantMap map = element.toMap();
        DanbooruPost* post = new DanbooruPost(map);
        StoredTransferJob* pixmapJob = KIO::storedGet(post->thumbnailUrl(),
            KIO::NoReload, KIO::HideProgressInfo);
        qDebug() << "Basic job info";
        qDebug() << post->id() << post->thumbnailUrl() << post->fileUrl();
        QVariant variant;
        variant.setValue(post);
        pixmapJob->setProperty("danbooruPost", variant);
        connect(pixmapJob, SIGNAL(result(KJob*)), this,
                SLOT(downloadThumbnail(StoredTransferJob*)));
    }

我被这个错误弄糊涂了。我可能做错了什么？

Answer 1

您已经在全局命名空间中，在namespace Danbooru之外，正向声明了class DanbooruPost。您最终得到了两个不同的类，::DanbooruPost和::Danbooru::DanbooruPost。

如果您无意这样做，请从全局命名空间中删除正向声明。