Qt: 网络编程之UDP（理论+实例）

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理论：

Qt 网络之UDP 网络基础学习是本文要介绍的内容，UDP（User Datagram Protocol即用户数据报协议）是一个轻量级的，不可靠的，面向数据报的无连接协议。对于UDP我们不再进行过多介绍，如果你对UDP不是很了解，而且不知道它有什么用，那么我们这里就举个简单的例子：我们现在几乎每个人都使用的腾讯QQ，其聊天时就是使用UDP协议进行消息发送的。就像QQ那样，当有很多用户，发送的大部分都是短消息，要求能及时响应，并且对安全性要求不是很高的情况下使用UDP协议。

　　在Qt中提供了QUdpSocket 类来进行UDP数据报（datagrams）的发送和接收。这里我们还要了解一个名词Socket，也就是常说的“套接字” 。 Socket简单地说，就是一个IP地址加一个port端口。因为我们要传输数据，就要知道往哪个机子上传送，而IP地址确定了一台主机，但是这台机子上可能运行着各种各样的网络程序，我们要往哪个程序中发送呢？这时就要使用一个端口来指定UDP程序。所以说，Socket指明了数据报传输的路径。

实例：

功能：server（图右）端每隔一秒钟，想UDP管道中写入数据，client（图左）端从管道中读出数据，并显示到界面上。

效果图：

服务器端源码：

//weatherballon.h

#ifndef WEATHERBALLON_H
#define WEATHERBALLON_H

#include <QPushButton>
#include <QTimer>
#include <QUdpSocket>

class WeatherBallon : public QPushButton
{
    Q_OBJECT

public:
    WeatherBallon(QWidget *parent = 0);
    ~WeatherBallon();

    double temperature() const;
    double humidity() const;
    double altitude() const;

private slots:
    void onSendDatagram();

private:
    QUdpSocket mUdpSocket;
    QTimer timer;
};

#endif // WEATHERBALLON_H

//weatherballon.cpp

#include <QDateTime>
#include <QIODevice>
#include <QByteArray>
#include "weatherballon.h"

WeatherBallon::WeatherBallon(QWidget *parent) : QPushButton (tr("quit"),parent)
{
    connect(this,SIGNAL(clicked(bool)),this,SLOT(close()));
    connect(&timer,SIGNAL(timeout()),this,SLOT(onSendDatagram()));

    timer.start(1000);
    setWindowTitle(tr("Weather Server"));
}

WeatherBallon::~WeatherBallon()
{

}

double WeatherBallon::temperature() const
{
    return -20.0 + (2.0 * std::rand() / (RAND_MAX + 1.0));
}

double WeatherBallon::humidity() const
{
    return 20.0 + (2.0 * std::rand() / (RAND_MAX + 1.0));
}

double WeatherBallon::altitude() const
{
    return 7000 + (100.0 * std::rand() / (RAND_MAX + 1.0));
}

void WeatherBallon::onSendDatagram()
{
    QByteArray datagram;
    QDataStream out(&datagram, QIODevice::WriteOnly);
    out.setVersion(QDataStream::Qt_5_7);

    out<<QDateTime::currentDateTime() <<temperature() << humidity() <<altitude();
    mUdpSocket.writeDatagram(datagram,QHostAddress::LocalHost ,5824);
}

客户端源码：

//weatherstation.h

#ifndef WEATHERSTATION_H
#define WEATHERSTATION_H

#include <QDialog>
#include <QLabel>
#include <QLineEdit>
#include <QtNetwork/QUdpSocket>

class WeatherStation : public QDialog
{
    Q_OBJECT

public:
    WeatherStation(QWidget *parent = 0);
    ~WeatherStation();

private slots:
    void onProcessPendingDatagrams();

private:
    QUdpSocket mUdpSocket;
    QLabel *mDataLabel;
    QLabel *mTimeLabel;
    QLabel *mTemperatureLabel;
    QLabel *mhumidtyLabel;
    QLabel *mAltitudeLabel;
    QLineEdit *mDateLineEdit;
    QLineEdit *mTimeLineEdit;
    QLineEdit *mTemperatureLineEdit;
    QLineEdit *mHunidityLineEdit;
    QLineEdit *mAltitudeLineEdit;
};

#endif // WEATHERSTATION_H

//weatherstation.cpp

#include <QGridLayout>
#include <QTimer>
#include <QDateTime>
#include "weatherstation.h"

WeatherStation::WeatherStation(QWidget *parent)
    : QDialog(parent)
{
    mUdpSocket.bind(5824);
    connect(&mUdpSocket,SIGNAL(readyRead()),SLOT(onProcessPendingDatagrams()));

    mDataLabel = new QLabel(tr("Data:"));
    mTimeLabel = new QLabel(tr("Time:"));
    mTemperatureLabel = new QLabel(tr("Temperature:"));
    mhumidtyLabel = new QLabel(tr("Hunidity:"));
    mAltitudeLabel = new QLabel(tr("Altitude:"));

    mDateLineEdit = new QLineEdit;
    mTimeLineEdit = new QLineEdit;
    mTemperatureLineEdit = new QLineEdit;
    mHunidityLineEdit = new QLineEdit;
    mAltitudeLineEdit = new QLineEdit;

    mDateLineEdit->setReadOnly(true);
    mTimeLineEdit->setReadOnly(true);
    mTemperatureLineEdit->setReadOnly(true);
    mHunidityLineEdit->setReadOnly(true);
    mAltitudeLineEdit->setReadOnly(true);

    QGridLayout *mainLayout = new QGridLayout;
    mainLayout->addWidget(mDataLabel,0,0);
    mainLayout->addWidget(mDateLineEdit,0,1);
    mainLayout->addWidget(mTimeLabel,1,0);
    mainLayout->addWidget(mTimeLineEdit,1,1);
    mainLayout->addWidget(mTemperatureLabel,2,0);
    mainLayout->addWidget(mTemperatureLineEdit,2,1);
    mainLayout->addWidget(mhumidtyLabel,3,0);
    mainLayout->addWidget(mHunidityLineEdit,3,1);
    mainLayout->addWidget(mAltitudeLabel,4,0);
    mainLayout->addWidget(mAltitudeLineEdit,4,1);

    setLayout(mainLayout);
    setWindowTitle(tr("Weather Station"));
}

WeatherStation::~WeatherStation()
{

}

void WeatherStation::onProcessPendingDatagrams()
{
    QByteArray datagram;

    while(mUdpSocket.hasPendingDatagrams()) //是否有数据包等待读取
    {
        datagram.resize(mUdpSocket.pendingDatagramSize()); //
        mUdpSocket.readDatagram(datagram.data(), datagram.size());
    }

    QDateTime dateTime;
    double temperature;
    double humidity;
    double altitude;

    QDataStream in(&datagram,QIODevice::ReadOnly); //从datagram中读取数据
    in.setVersion(QDataStream::Qt_5_7);
    in>>dateTime >> temperature >>humidity >>altitude;

    mDateLineEdit->setText(dateTime.date().toString());
    mTimeLineEdit->setText(dateTime.time().toString());
    mTemperatureLineEdit->setText(tr("%1 C").arg(temperature));
    mHunidityLineEdit->setText(tr("%1%").arg(humidity));
    mAltitudeLineEdit->setText(tr("%1 m").arg(altitude));
}

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