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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
qBeijing,cn查询中国北京的天气
modejson返回格式为 JSON
unitsmetric返回单位为公制
langzh_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);

WeatherInfoWeatherDetail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:

 
 
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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:

Qt 学习之路 2(66):访问网络(2)-LMLPHP

 
04-25 07:00