Qt 学习之路 2（66）：访问网络（2）

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Qt 学习之路 2（66）：访问网络（2）

Qt 学习之路 2（66）：访问网络（2）

 豆子  2013年10月31日  Qt 学习之路 2  27条评论

上一章我们了解了NetWorker类的简单实现。不仅如此，我们还提到了几个 C++ 开发时常用的设计模式。这些在接下来得代码中依然会用到。

现在我们先来研究下 OpenWeatherMap 的相关 API。之所以选择 OpenWeatherMap，主要是因为这个网站提供了简洁的 API 接口，非常适合示例程序，并且其开发也不需要额外申请 App ID。OpenWeatherMap 的 API 可以选择返回 JSON 或者 XML，这里我们选择使用 JSON 格式。在进行查询时，OpenWeatherMap 支持使用城市名、地理经纬度以及城市 ID，为简单起见，我们选择使用城市名。我们先来看一个例子：http://api.openweathermap.org/data/2.5/weather?q=Beijing,cn&mode=json&units=metric&lang=zh_cn。下面是这个链接的参数分析：

参数名字	传入值	说明
q	Beijing,cn	查询中国北京的天气
mode	json	返回格式为 JSON
units	metric	返回单位为公制
lang	zh_cn	返回语言为中文

点击链接，服务器返回一个 JSON 字符串（此时你应该能够使用浏览器看到这个字符串）：

 

 

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{"coord":{"lon":116.397232,"lat":39.907501},"sys":{"country":"CN","sunrise":1381530122,"sunset":1381570774},"weather":[{"id":800,"main":"Clear","description":"晴","icon":"01d"}],"base":"gdps stations","main":{"temp":20,"pressure":1016,"humidity":34,"temp_min":20,"temp_max":20},"wind":{"speed":2,"deg":50},"clouds":{"all":0},"dt":1381566600,"id":1816670,"name":"Beijing","cod":200}

我们从这里找到 JSON 各个字段的含义。现在我们关心的是：时间（dt）；气温（temp）；气压（pressure）；湿度（humidity）和天气状况（weather）。基于此，我们设计了WeatherInfo类，用于封装服务器返回的信息：

 

 

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class WeatherDetail { public:     WeatherDetail();     ~WeatherDetail();       QString desc() const;     void setDesc(const QString &desc);       QString icon() const;     void setIcon(const QString &icon);   private:     class Private;     friend class Private;     Private *d; };   class WeatherInfo { public:     WeatherInfo();     ~WeatherInfo();       QString cityName() const;     void setCityName(const QString &cityName);       quint32 id() const;     void setId(quint32 id);       QDateTime dateTime() const;     void setDateTime(const QDateTime &dateTime);       float temperature() const;     void setTemperature(float temperature);       float humidity() const;     void setHumidity(float humidity);       float pressure() const;     void setPressure(float pressure);       QList<WeatherDetail *> details() const;     void setDetails(const QList<WeatherDetail *> details);   private:     class Private;     friend class Private;     Private *d; };   QDebug operator <<(QDebug dbg, const WeatherDetail &w); QDebug operator <<(QDebug dbg, const WeatherInfo &w);

WeatherInfo和WeatherDetail两个类相互合作存储我们所需要的数据。由于是数据类，所以只有单纯的 setter 和 getter 函数，这里不再把源代码写出来。值得说明的是最后两个全局函数：

 

 

1 2	QDebug operator <<(QDebug dbg, const WeatherDetail &w); QDebug operator <<(QDebug dbg, const WeatherInfo &w);

我们重写了<<运算符，以便能够使用类似qDebug() << weatherInfo;这样的语句进行调试。它的实现是这样的：

 

 

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QDebug operator <<(QDebug dbg, const WeatherDetail &w) {     dbg.nospace() << "("                   << "Description: " << w.desc() << "; "                   << "Icon: " << w.icon()                   << ")";     return dbg.space(); }   QDebug operator <<(QDebug dbg, const WeatherInfo &w) {     dbg.nospace() << "("                   << "id: " << w.id() << "; "                   << "City name: " << w.cityName() << "; "                   << "Date time: " << w.dateTime().toString(Qt::DefaultLocaleLongDate) << ": " << endl                   << "Temperature: " << w.temperature() << ", "                   << "Pressure: " << w.pressure() << ", "                   << "Humidity: " << w.humidity() << endl                   << "Details: [";     foreach (WeatherDetail *detail, w.details()) {         dbg.nospace() << "( Description: " << detail->desc() << ", "                       << "Icon: " << detail->icon() << "), ";     }     dbg.nospace() << "] )";     return dbg.space(); }

这两个函数虽然比较长，但是很简单，这里不再赘述。

下面我们来看主窗口：

 

 

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class MainWindow : public QMainWindow {     Q_OBJECT public:     MainWindow(QWidget *parent = 0);     ~MainWindow();   private:     class Private;     friend class Private;     Private *d; };

正如前面所说的，这里依然使用了 d 指针模式。头文件没有什么可说的。MainWindow::Private的实现依旧简单：

 

 

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class MainWindow::Private { public:     Private()     {         netWorker = NetWorker::instance();     }       void fetchWeather(const QString &cityName) const     {         netWorker->get(QString("http://api.openweathermap.org/data/2.5/weather?q=%1&mode=json&units=metric&lang=zh_cn").arg(cityName));     }       NetWorker *netWorker; };

我们将MainWindow所需要的NetWorker作为MainWindow::Private的一个成员变量。MainWindow::Private提供了一个fetchWeather()函数。由于NetWorker提供的函数都是相当底层的，为了提供业务级别的处理，我们将这样的函数封装在MainWindow::Private中。当然，你也可以在NetWorker中直接提供类似的函数，这取决于你的系统分层设计。

 

 

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MainWindow::MainWindow(QWidget *parent)     : QMainWindow(parent),       d(new MainWindow::Private) {     QComboBox *cityList = new QComboBox(this);     cityList->addItem(tr("Beijing"), QLatin1String("Beijing,cn"));     cityList->addItem(tr("Shanghai"), QLatin1String("Shanghai,cn"));     cityList->addItem(tr("Nanjing"), QLatin1String("Nanjing,cn"));     QLabel *cityLabel = new QLabel(tr("City: "), this);     QPushButton *refreshButton = new QPushButton(tr("Refresh"), this);     QHBoxLayout *cityListLayout = new QHBoxLayout;     cityListLayout->setDirection(QBoxLayout::LeftToRight);     cityListLayout->addWidget(cityLabel);     cityListLayout->addWidget(cityList);     cityListLayout->addWidget(refreshButton);       QVBoxLayout *weatherLayout = new QVBoxLayout;     weatherLayout->setDirection(QBoxLayout::TopToBottom);     QLabel *cityNameLabel = new QLabel(this);     weatherLayout->addWidget(cityNameLabel);     QLabel *dateTimeLabel = new QLabel(this);     weatherLayout->addWidget(dateTimeLabel);       QWidget *mainWidget = new QWidget(this);     QVBoxLayout *mainLayout = new QVBoxLayout(mainWidget);     mainLayout->addLayout(cityListLayout);     mainLayout->addLayout(weatherLayout);     setCentralWidget(mainWidget);     resize(320, 120);     setWindowTitle(tr("Weather"));       connect(d->netWorker, &NetWorker::finished, [=] (QNetworkReply *reply) {         qDebug() << reply;         QJsonParseError error;         QJsonDocument jsonDocument = QJsonDocument::fromJson(reply->readAll(), &error);         if (error.error == QJsonParseError::NoError) {             if (!(jsonDocument.isNull() || jsonDocument.isEmpty()) && jsonDocument.isObject()) {                 QVariantMap data = jsonDocument.toVariant().toMap();                 WeatherInfo weather;                 weather.setCityName(data[QLatin1String("name")].toString());                 QDateTime dateTime;                 dateTime.setTime_t(data[QLatin1String("dt")].toLongLong());                 weather.setDateTime(dateTime);                 QVariantMap main = data[QLatin1String("main")].toMap();                 weather.setTemperature(main[QLatin1String("temp")].toFloat());                 weather.setPressure(main[QLatin1String("pressure")].toFloat());                 weather.setHumidity(main[QLatin1String("humidity")].toFloat());                 QVariantList detailList = data[QLatin1String("weather")].toList();                 QList<WeatherDetail *> details;                 foreach (QVariant w, detailList) {                     QVariantMap wm = w.toMap();                     WeatherDetail *detail = new WeatherDetail;                     detail->setDesc(wm[QLatin1String("description")].toString());                     detail->setIcon(wm[QLatin1String("icon")].toString());                     details.append(detail);                 }                 weather.setDetails(details);                   cityNameLabel->setText(weather.cityName());                 dateTimeLabel->setText(weather.dateTime().toString(Qt::DefaultLocaleLongDate));             }         } else {             QMessageBox::critical(this, tr("Error"), error.errorString());         }         reply->deleteLater();     });     connect(refreshButton, &QPushButton::clicked, [=] () {         d->fetchWeather(cityList->itemData(cityList->currentIndex()).toString());     }); }   MainWindow::~MainWindow() {     delete d;     d = 0; }

接下来我们来看MainWindow的构造函数和析构函数。构造函数虽然很长但是并不复杂，主要是对界面的构建。我们这里略过这些界面的代码，直接看两个信号槽的连接。

 

 

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connect(d->netWorker, &NetWorker::finished, [=] (QNetworkReply *reply) {         QJsonParseError error;         QJsonDocument jsonDocument = QJsonDocument::fromJson(reply->readAll(), &error);         if (error.error == QJsonParseError::NoError) {             if (!(jsonDocument.isNull() || jsonDocument.isEmpty()) && jsonDocument.isObject()) {                 QVariantMap data = jsonDocument.toVariant().toMap();                 WeatherInfo weather;                 weather.setCityName(data[QLatin1String("name")].toString());                 QDateTime dateTime;                 dateTime.setTime_t(data[QLatin1String("dt")].toLongLong());                 weather.setDateTime(dateTime);                 QVariantMap main = data[QLatin1String("main")].toMap();                 weather.setTemperature(main[QLatin1String("temp")].toFloat());                 weather.setPressure(main[QLatin1String("pressure")].toFloat());                 weather.setHumidity(main[QLatin1String("humidity")].toFloat());                 QVariantList detailList = data[QLatin1String("weather")].toList();                 QList<WeatherDetail *> details;                 foreach (QVariant w, detailList) {                     QVariantMap wm = w.toMap();                     WeatherDetail *detail = new WeatherDetail;                     detail->setDesc(wm[QLatin1String("description")].toString());                     detail->setIcon(wm[QLatin1String("icon")].toString());                     details.append(detail);                 }                 weather.setDetails(details);                   cityNameLabel->setText(weather.cityName());                 dateTimeLabel->setText(weather.dateTime().toString(Qt::DefaultLocaleLongDate));             }         } else {             QMessageBox::critical(this, tr("Error"), error.errorString());         }         reply->deleteLater();     });     connect(refreshButton, &QPushButton::clicked, [=] () {         d->fetchWeather(cityList->itemData(cityList->currentIndex()).toString());     });

由于使用了 Qt5，我们选择新的连接语法。第一个connect()函数中，我们按照 API 文档中描述的那样对服务器返回的 JSON 字符串进行解析，然后将数据填充到一个WeatherInfo的对象。然后操作界面的两个控件显示数据。值得注意的是函数的最后一行，reply->deleteLater();。当网络请求结束时，delete 服务器返回的QNetworkReply对象是用户的责任。用户需要选择一个恰当的时机进行 delete 操作。但是，我们不能直接在finiahed()信号对应的槽函数中调用delete运算符。相反，我们需要使用deleteLater()函数，正如前面代码中显示的那样。第二个槽函数则相对简单，仅仅是重新获取新的数据。

选择我们可以运行下程序了：