c++ - Qt GUI 变得 react 迟钝，发出信号的速度太快

Question

我有一个小型聊天客户端，可以将所有历史记录存储在 sqlite 数据库中。当用户单击我的应用程序中的 history 选项卡时，我的应用程序会获取所有相关历史记录并将其显示在 QWebView 中。我从下面的后台线程 dbThread 获取数据，然后发送信号以相应地更新 QWebView。

这工作正常，直到数据库增长。当数据库变大时，应用程序开始几乎崩溃。根据 database 的大小，GUI 有几秒钟没有响应，直到所有内容都加载完毕(4-6 秒)。

我尝试在信号上添加 Qt::QueuedConnection 并且像上面提到的那样，我正在处理来自 background thread< 的所有 database 查询.

我猜我发射信号的速度太快了。有什么解决办法吗？

信号

connect(dbtrad, SIGNAL(addAllHistoryMessage(QString, QString, QString, QString, QString)), this, SLOT(addAllHistoryMessage(QString, QString, QString, QString, QString)), Qt::QueuedConnection);
connect(dbtrad, SIGNAL(addAllHistoryMessageInner(QString, QString, QString, QString, QString)), this, SLOT(addAllHistoryMessageInner(QString, QString, QString, QString, QString)), Qt::QueuedConnection);

从 sqlite 数据库中获取历史的代码:

// Loads all local history
void dbThread::loadAllHistory(QString agentID, QString agentName) {
    bool ret = false;
    bool retInner = false;
    QString retVal = "";

    QDateTime dateTime = dateTime.currentDateTime();
    QString dateTimeForTodayCheck = dateTime.toString("yyyy-MM-dd");

    if (db.isOpen()) {
        QSqlQuery query(db);
        QSqlQuery queryInner(db);

        ret = query.exec(QString("SELECT channelID, sender, time, message from chatHistory WHERE sender != 'ServerMessage' AND channelID NOT LIKE '%Agent%' GROUP BY channelID order by time DESC;"));

        if (ret) {

            while (query.next()) {    
                QString channelID = query.value(0).toString();
                QString sender = query.value(1).toString();
                QString time = query.value(2).toString();
                QString msg = query.value(3).toString();


                QString timeStr;
                QString fmt = "yyyy-MM-dd hh:mm:ss";
                QDateTime dt = QDateTime::fromString(time, fmt);
                QDateTime dtCompare = QDateTime::fromString(time, fmt);

                if(dateTimeForTodayCheck == dtCompare.toString("yyyy-MM-dd")) { // If today
                    timeStr = "Today " + dt.toString("hh:mm");
                } else {
                    timeStr = dt.toString("dd MMM yyyy");
                }

                if(sender == agentID) {
                    sender = agentName;
                }
                // Grab all the tags
                QString tempTagsForChannelID = getHistoryTagsString(channelID);

                emit addAllHistoryMessage(channelID, sender, timeStr, msg, tempTagsForChannelID);

                // Load sub-history
                retInner = queryInner.exec(QString("SELECT * from chatHistory WHERE sender != 'ServerMessage' AND channelID = '%1' and message != '%2' order by time DESC;").arg(channelID).arg(msg));

                if (retInner) {
                    while (queryInner.next()) {
                        QString channelIDInner = queryInner.value(0).toString();
                        QString senderInner = queryInner.value(1).toString();
                        QString timeInner = queryInner.value(4).toString();
                        QString msgInner = queryInner.value(2).toString();

                        QString timeStr2;
                        QString fmt = "yyyy-MM-dd hh:mm:ss";
                        QDateTime dt = QDateTime::fromString(timeInner, fmt);
                        QDateTime dtCompare = QDateTime::fromString(timeInner, fmt);

                        if(dateTimeForTodayCheck == dtCompare.toString("yyyy-MM-dd")) { // If today
                            timeStr2 = "Today " + dt.toString("hh:mm");
                        } else {
                            timeStr2 = dt.toString("dd MMM yyyy");
                        }

                        if(senderInner == agentID) {
                            senderInner = agentName;
                        }

                        emit addAllHistoryMessageInner(channelIDInner, senderInner, timeStr2, msgInner, tempTagsForChannelID);
                    }
                }
            }
        }
    }
}

我要更新的代码:

void MainWindow::addAllHistoryMessageInner(QString channelIDInner, QString senderInner, QString timeStr2, QString msgInner, QString tempTagsForChannelID) {
    ui->webViewHistory->page()->mainFrame()->evaluateJavaScript("$('#history tbody').append('<tr id=\"" + channelIDInner+ "\" class=\"hiddenRow\"><td>" + senderInner + "</td><td align=\"center\">" + timeStr2 + "</td><td align=\"center\" style=\"word-wrap:break-word;\">" + msgInner.remove(QRegExp("<[^>]*>")) + "</td><td align=\"center\">" + tempTagsForChannelID + "</td></tr>');undefined");
}

void MainWindow::addAllHistoryMessage(QString channelID, QString sender, QString timeStr, QString msg, QString tempTagsForChannelID) {
    ui->webViewHistory->page()->mainFrame()->evaluateJavaScript("$('#history tbody').append('<tr id=\"" + channelID + "\"><td>" + sender + "</td><td align=\"center\">" + timeStr + "</td><td align=\"center\" style=\"word-wrap:break-word;\">" + msg.remove(QRegExp("<[^>]*>")) + "</td><td align=\"center\" style=\"word-wrap:break-word;\">" + tempTagsForChannelID + "</td></tr>');undefined");
}

编辑:dbThread 的实现

thread = new QThread(this);
dbtrad = new dbThread();
dbtrad->moveToThread(thread);

编辑 2:这就是我如何调用 loadAllHistory

我创建一个信号:

connect(this, SIGNAL(loadAllHistoryS(QString, QString)), dbtrad, SLOT(loadAllHistory(QString, QString)));

然后这样调用它:

emit loadAllHistoryS(agentID, agentName);

Answer 1

问题是，您的主线程因 innerQuery 中的每一行而中断。这破坏了在单独线程中加载数据的好处。可能跨线程边界的信号/槽通信的开销甚至高于从数据库加载单行的成本。

我建议在QList 实例中收集行while 循环。完成后，通过一次信号调用将完整结果推送到主线程:

首先声明一个用于存储历史项的简单类:

class HistoryItem {
    public:
        QString channelID;
        /* additonal fields omitted for brevity */
        /* also, private fields with getters and setters would be better */
}

然后，在 while 循环之前创建此类对象的列表:

QList<HistoryItem*> innerResult;
while (queryInner.next()) {
      /* snip */
      HistoryItem* item = new HistoryItem();
      item.channelId = channelIDInner;
      /* more lines ommited */
      innerResult.append(historyItem);
}
emit historyLoaded(innerResult);

显然，您还需要在工作类中匹配信号定义:

Q_SIGNAL void historyLoaded(QList<HistoryItem*> result);    

---

另外如评论中所述，您必须使用 QThread::start() 启动后台线程。