(66)访问网络(2)
最后更新于:2022-04-01 06:30:43
#(66):访问网络(2)
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](http://api.openweathermap.org/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](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):
~~~
{"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](http://bugs.openweathermap.org/projects/api/wiki/Weather_Data)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:
~~~
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:
~~~
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:
~~~
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:
~~~
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:
~~~
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。
~~~
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。
~~~
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:
[![](https://docs.gechiui.com/gc-content/uploads/sites/kancloud/2015-12-29_56823274bbd0d.png)](http://files.devbean.net/images/2013/10/weather-demo.png)