QT：使用移動語義將信號連接到插槽

Question

好的，我有這樣的事情：

void EmailReceiverThread::foreachEmailAccount(ConfigEmailAccount account)
{
    Email email;
    EmailReader emailReader(account);
    while (emailReader.pollEmail(email))
    {
        writeEmailToDatabase(email);
    }
}

ForeachEmailAccount 是EmailReceiverThread 中的一個槽。 它是從 run() 方法調用的：

GetConfigEmailDAO* accountReader = new GetConfigEmailDAO(type, m_channel);
connect(accountReader, SIGNAL(emailAccount(ConfigEmailAccount)),
        this, SLOT(foreachEmailAccount(ConfigEmailAccount)), Qt::QueuedConnection);
DbThread::postAction(accountReader);

GetConfigEmailDAO 執行查詢，獲取電子郵件帳戶並發出：

emit emailAccount(account);

到目前為止，這有效。 問題是，我正在復制 ConfigEmailAccount 類。 我想避免性能下降。 所以，我的想法是使用 c++11 移動語義發出帳戶：

emit emailAccount(std::move(account));

我用新語法重寫了插槽和信號：

void foreachEmailAccount(ConfigEmailAccount&& account);

不幸的是，這行不通。 我有下一個編譯錯誤：

moc_emailreceiverthread.cpp:88: error: cannot bind ‘ConfigEmailAccount’ lvalue to ‘ConfigEmailAccount&&’
     case 1: _t->foreachEmailAccount((*reinterpret_cast< ConfigEmailAccount(*)>(_a[1]))); break;

我能做什么？

這里的最小可驗證示例：

#include <QCoreApplication>
#include <QObject>

class ConfigEmailAccount
{
    QString some_data;
};

class GetConfigEmailDAO : public QObject
{
    Q_OBJECT
public:
    void execute();

signals:
    void emailAccount(ConfigEmailAccount&& account);
};

void GetConfigEmailDAO::execute()
{
    ConfigEmailAccount account;
    emit emailAccount(std::move(account));
}

class EmailReceiverThread : public QObject
{
    Q_OBJECT
public:
    void execute();
public slots:
    void foreachEmailAccount(ConfigEmailAccount&& account);
};

void EmailReceiverThread::execute()
{

    GetConfigEmailDAO* accountReader = new GetConfigEmailDAO;
    connect(accountReader, SIGNAL(emailAccount(ConfigEmailAccount)),
            this, SLOT(foreachEmailAccount(ConfigEmailAccount)), Qt::QueuedConnection);
    accountReader->execute();
}

void EmailReceiverThread::foreachEmailAccount(ConfigEmailAccount&& account)
{

}

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);
    qRegisterMetaType<ConfigEmailAccount>("ConfigEmailAccount");
    EmailReceiverThread reader;
    reader.execute();
    return a.exec();
}

#include "main.moc"

Answer 1

最后我采用了QT的淺拷貝機制：
http://doc.qt.io/qt-5.6/qshareddatapointer.html#details