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这是出于纯粹的测试目的和我的好奇心。我使用我的 DataDownloader 类从服务器获取数据列表。它适用于不同的 url，例如http://tiny-file-url、http://big-file-url。但是如果我传入两个相同的 url，http://tiny-file-url，http://tiny-file-url，并且来自http://tiny-file-url的数据很小，那么第二个回复来自 QNetworkAccessManager 是空的。然而，两个http://big-file-url似乎工作。我想知道 QNetworkAccessManager 在从同一个 url 请求小数据时是否有一些魔力？我似乎无法在 Qt 文档站点上获得任何相关信息。

这是我的DataDownloader课：

class DataDownloader : public QObject
{
    Q_OBJECT

public:
    explicit DataDownloader(QObject* parent = 0);
    virtual ~DataDownloader();

    QByteArray data() const;
    void cancel();
    void download(QUrl url);

    signals:
    void isComplete();

    private slots:
    void complete(QNetworkReply* reply);

    private:
    QNetworkAccessManager m_NetworkManager;
    QByteArray m_Data;
    QNetworkReply* m_pReply;
};

DataDownloader::DataDownloader(QUrl url, QObject* parent) :QObject(parent)
{
    connect(&m_NetworkManager, SIGNAL(finished(QNetworkReply*)),
            SLOT(complete(QNetworkReply*)));
}

DataDownloader::~DataDownloader()
{
}

void DataDownloader::complete(QNetworkReply* reply)
{
    // in the first download it returns data
    // but the second time m_Data is empty
    m_Data = reply->readAll();
    reply->deleteLater();

    if (!m_Data.isEmpty()) {
        // no signal on the second try
        emit isComplete();
    }
}

QByteArray DataDownloader::data() const
{
    return m_Data;
}

void DataDownloader::cancel()
{
    m_pReply->abort();
}

void DataDownloader::download(QUrl url)
{
    QNetworkRequest request(url);
    m_pReply = m_NetworkManager.get(request);
}

调用它的代码DataDownloader如下：

void PluginManager::downloadPlugins()
{
    m_DownloadIndex++;

    savePlugin();

    if (m_DownloadIndex < m_PluginList.size()) {
        QUrl url;
        // alway return the same url here
        QString pluginUrl = getPluginUrl(m_PluginList.at(m_DownloadIndex));
        url.setUrl(pluginUrl);

        if (m_pPluginDownloader == NULL) {
            m_pPluginDownloader = new DataDownloader();
            // call this function again when isComplete is signaled
            connect(m_pPluginDownloader, SIGNAL(isComplete()), this, SLOT(downloadPlugins()));
        }
        m_pPluginDownloader->download(url);
    }
}
4

1 回答 1

1

我认为这里是在你将它连接到插槽isComplete之前发出的。downloadPlugins尝试先连接此信号，然后执行下载操作：

m_pPluginDownloader = new DataDownloader(url);

connect(m_pPluginDownloader, SIGNAL(isComplete()), this, SLOT(downloadPlugins()));

m_pPluginDownloader.download();

而不是在构造函数中执行 get 操作，而是在一个名为的插槽中执行它download：

void DataDownloader::download()
{
    QNetworkRequest request(url);
    m_pReply = m_NetworkManager.get(request);
}

另一点是不必DataDownloader每次都创建一个新实例。您可以在构造函数中创建一个实例并在那里PluginManager连接isComplete信号。然后，您可以在download插槽中提供 url 作为参数。

于 2015-02-06T18:58:54.573 回答