为什么我得到 QJsonValue(undefined)？

Question

当我向 API 请求获取出价时，我得到的 QJsonValue 未定义，并且稍后无法显示它，我做错了什么？

{
    QApplication a(argc, argv);
    MainWindow w;
    w.show();
    QNetworkAccessManager m_manager;
   // make request
    QNetworkRequest request = QNetworkRequest(QUrl("https://api.30.bossa.pl/API/GPW/v2/Q/C/_cat_name/WIG20?_t=1637005413888"));
     QNetworkReply* reply = m_manager.get(request);
     QObject::connect(reply, &QNetworkReply::finished, [reply]() {
       QByteArray rawData = reply->readAll();
       QString textData(rawData);
       qDebug() << textData;
       QJsonDocument doc = QJsonDocument::fromJson(textData.toUtf8());
       QJsonObject obj = doc.object();
       qDebug() << obj;
       QJsonValue value = obj.value(QString("_quote_min"));
       qDebug() << obj.value(QString("_quote_min"));;
       qDebug() << "Bid value is" << value.toString();;
       reply->deleteLater(); // make sure to clean up
     });
    return a.exec();
}

这是我的 json:

QJsonObject({"_count":1,"_d":[{"_h":"Własne - 19 listopada 2021 17:15","_hs":"Własne","_max_quote_dtm":"19 listopada 2021","_max_quote_dtm_lc":"19 listopada, 17:15","_ret_quote_dtm":"2021-11-19","_t":[{"_30d_change_max":2453.57,"_30d_change_min":2221.68,"_ask_orders_nr":null,"_ask_size":null,"_ask_volume":null,"_bid_orders_nr":null,"_bid_size":null,"_bid_volume":null,"_change":"-1.02","_change_close_open":"-1.04","_change_max_min":"+2.91","_change_pnts":-23.13,"_change_proc":-1.02,"_change_settl_ref":null,"_change_suffix":"%","_change_type":"_change_proc","_debut":"0","_group":"X1","_is_indice":"1","_isin":"PL9999999987","_live":"0","_open_positions":null,"_phase":"Zamknięcie ostateczne","_quote":"2248.18","_quote_date":"2021.11.19","_quote_imp":"2276.90","_quote_max":"2286.37","_quote_min":"2221.68","_quote_open":"2271.91","_quote_ref":"2271.31","_quote_time":"17:15","_quote_type":"_quote","_quote_volume":null,"_settlement_price":null,"_step":"2","_sw_symbol_short":0,"_symbol":"WIG20","_symbol_short":"WIG20","_time":"17:15","_transactions_nr":null,"_turnover_value":1257698337,"_type_of_instrument":"0","_volume":null}]}],"_d_fx":{"_h":null,"_hs":null,"_max_quote_dtm":null,"_max_quote_dtm_lc":null,"_t":[]},"_i":[null],"_quote_date":null,"_symbol":["WIG20"],"_type":"C","message":"OK"})

Answer 1

如果您确信 JSON 结构将始终相同，那么您可以像下面这样找到您的值。（我将其分解为多个对象，并按照它们在 JSON 文件中的命名方式命名它们。）

    QJsonDocument doc = QJsonDocument::fromJson(textData.toUtf8());
    auto rootObj = doc.object();
    auto _d = rootObj.value("_d").toArray();
    auto _t = _d[0].toObject().value("_t").toArray();
    auto _quote_min = _t[0].toObject().value("_quote_min");
    qDebug() << _quote_min;

输出：

QJsonValue(string, "2221.68")

为什么我得到 QJsonValue(undefined)？

Why do i get QJsonValue(undefined)?

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qt

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