c++ - 如果指针指向一个新对象，信号/槽连接会发生什么

Question

我有一个带有以下代码的 uploader :

if(!_canceled) {
    _reply = _accessManager.put(request, item);

    if(_reply) { 
        _currentItem = item;

        bool status = connect(_reply, SIGNAL(uploadProgress(qint64, qint64)), this, SLOT(reportUploadProgress(qint64, qint64)));
        pantheios::log(pantheios::debug, "StorageProvider(): connection uploadProgress(qint64, qint64), status", pantheios::boolean(status));
        status = connect(_reply, SIGNAL(finished()), this, SLOT(handleFinishedRequest()));
        pantheios::log(pantheios::debug, "StorageProvider(): connection finished(), status", pantheios::boolean(status));

    } else {
        emit noReply();
        pantheios::log(pantheios::error, "StorageProvider(): no reply", item.toUtf8());
    }

然后在完成的插槽中我这样做:

QNetworkReply *reply =  qobject_cast<QNetworkReply*>(sender());

if(reply->error() > QNetworkReply::NoError) { 
    pantheios::log(pantheios::error, "StorageProvider(handleFinishedRequest) ", reply->errorString().toUtf8());

    if((reply->error() == QNetworkReply::TemporaryNetworkFailureError) || (reply->error() == QNetworkReply::ContentReSendError)) {
                    // retry the last request
        _reply = accessManager.put(reply->request(), _currentItem);
    }

} else {
    ...
}

此 StorageProvider 将能够处理不同的请求，并且回复将具有不同的连接，具体取决于它在哪个函数中创建。回复是一个成员变量的原因是我可以在我做下一个请求之前删除它。

所以，我的问题是，如果我重新指向回复，是否必须重新连接？插槽/信号连接到指针还是对象？另外，有没有更好的方法删除旧回复？

编辑:将已完成请求的处理程序的代码更改为此；

if(_currentReply->error() > QNetworkReply::NoError) { 
    pantheios::log(pantheios::error, "StorageProvider(handleFinishedRequest) ", _currentReply->errorString().toUtf8());

    if(((_currentReply->error() == QNetworkReply::TemporaryNetworkFailureError) || (_currentReply->error() == QNetworkReply::ContentReSendError)) && (_currentRetries < 4)) {

        QNetworkRequest lastRequest = _currentReply->request();
        _currentReply->deleteLater();

        _currentReply = _accessManager.put(lastRequest, _currentItem);

        if(_currentReply) { 

            bool status = connect(_currentReply, SIGNAL(uploadProgress(qint64, qint64)), this, SLOT(reportUploadProgress(qint64, qint64)));
            pantheios::log(pantheios::debug, "StorageProvider(retry): connection uploadProgress(qint64, qint64), status", pantheios::boolean(status));
            status = connect(_currentReply, SIGNAL(finished()), this, SLOT(handleFinishedRequest()));
            pantheios::log(pantheios::debug, "StorageProvider(retry): connection finished(), status", pantheios::boolean(status));

        } else {
            emit noReply();
            pantheios::log(pantheios::error, "StorageProvider(retry): AccessManager no reply");
        }
    }

}

Answer 1

信号连接到对象，而不是指针变量，所以你每次都必须建立新的连接。

要删除回复，只需在 finished() 槽的开头调用 deleteLater():

QNetworkReply *reply =  qobject_cast<QNetworkReply*>(sender());
reply->deleteLater();

这样它将在槽执行结束时被删除。

---

您可以通过将每个请求(初始请求加上所有重试)包装在其自己的 QObject 派生类中来避免使用 sender():

class PutRequest : public QObject {
Q_OBJECT
private:
     QNetworkAccessManager *_manager;
     QNetworkReply *_reply;
     QIODevice *_item; // Or whatever type the second parameter of put is
public:
     explicit PutRequest(QNetworkAccessManager *manager, QNetworkRequest *request, QIODevice *item, QObject *parent = 0)
       : QObject(parent), _manager, _reply(0), _item(item) 
     {            
         _reply = _manager.put(request, item);
         connectSignalsAndSlots();
     }       

private:
     void connectSignalsAndSlots() {
         // to delete the reply if the PutRequest object is destroyed
         reply_->setParent(this);
         // since the reply is encapsulated, the object has to emit its own
         // upload progress signal
         connect(_reply, SIGNAL(uploadProgress(qint64, qint64)), this, SIGNAL(uploadProgress(qint64, qint64)));
         connect(_reply, SIGNAL(finished()), this, SLOT(handleFinishedRequest()));
     }

private slots:
     void handleFinishedRequest() {
         _reply->deleteLater();
         if(reply->error() != QNetworkReply::NoError) {
               pantheios::log(pantheios::error, "StorageProvider(handleFinishedRequest) ", reply->errorString().toUtf8());

         if((_reply->error() == QNetworkReply::TemporaryNetworkFailureError) || (reply->error() == QNetworkReply::ContentReSendError)) {
            // retry the last request
            _reply = _manager.put(_reply->request(), _item);
            connectSignalsAndSlots();
         }

         } else {
         ...                 
             emit finished(this);
         }         
     }
signals:
     void uploadProgress(qint64, qint64);
     // emitted when the upload is successful (after the possible retries)
     void finished(PutRequest*);
};

你会像这样创建请求:

if(!_canceled) {
    PutRequest *putRequest = new PutRequest(_accessManager, request, item);

    // and you connect putRequest object signals to whatever you connected _reply to