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一.UDP通信

1.QT中实现UDP通信主要用到了以下类：QUdpSocket、QHostAddress；

2.UdpServer是服务器端，用于监听客户端发送的消息并回复同样的消息；

  UdpClient是客户端，用于向服务器发送一条消息，并等待来自服务器的回复；

3.UDP与TCP的区别

UDP像写信，只要知道地址就可以发

TCP像打电话，只有两人同时在线才能通信

4.UDP多播组播

二．示例代码

本示例代码实现功能为本地管理的组播收发功能。

1.mainwindow.h

#ifndef MAINWINDOW_H

#define MAINWINDOW_H

#include <QMainWindow>

#include    <QUdpSocket>

#include    <QLabel>

namespace Ui {

class MainWindow;

}

class MainWindow : public QMainWindow

{

    Q_OBJECT

private:

    QLabel  *LabSocketState;

    QUdpSocket  *udpSocket;//用于与连接的客户端通讯的QTcpSocket

    QHostAddress    groupAddress;//组播地址

    QString getLocalIP();//获取本机IP地址

public:

    explicit MainWindow(QWidget *parent = 0);

    ~MainWindow();

private slots:

//自定义槽函数

    void    onSocketStateChange(QAbstractSocket::SocketState socketState);

    void    onSocketReadyRead();//读取socket传入的数据

    

    void on_actStart_triggered();

    void on_actStop_triggered();

    void on_actClear_triggered();

    void on_actHostInfo_triggered();

    void on_btnMulticast_clicked();

private:

    Ui::MainWindow *ui;

};

#endif // MAINWINDOW_H

2.mainwindow.cpp

#include "mainwindow.h"

#include "ui_mainwindow.h"

#include    <QtNetwork>

QString MainWindow::getLocalIP()

{

    QString hostName=QHostInfo::localHostName();//本地主机名

    QHostInfo   hostInfo=QHostInfo::fromName(hostName);

    QString   localIP="";

    QList<QHostAddress> addList=hostInfo.addresses();//

    if (!addList.isEmpty())

    for (int i=0;i<addList.count();i++)

    {

        QHostAddress aHost=addList.at(i);

        if (QAbstractSocket::IPv4Protocol==aHost.protocol())

        {

            localIP=aHost.toString();

            break;

        }

    }

    return localIP;

}

MainWindow::MainWindow(QWidget *parent) :

    QMainWindow(parent),

    ui(new Ui::MainWindow)

{

    ui->setupUi(this);

    LabSocketState=new QLabel("Socket状态：");//

    LabSocketState->setMinimumWidth(200);

    ui->statusBar->addWidget(LabSocketState);

    QString localIP=getLocalIP();//本地主机名

    this->setWindowTitle(this->windowTitle()+"----本机IP："+localIP);

    udpSocket=new QUdpSocket(this);//用于与连接的客户端通讯的QTcpSocket

    udpSocket->setSocketOption(QAbstractSocket::MulticastTtlOption,1);

    connect(udpSocket,SIGNAL(stateChanged(QAbstractSocket::SocketState)),

            this,SLOT(onSocketStateChange(QAbstractSocket::SocketState)));

    onSocketStateChange(udpSocket->state());

    connect(udpSocket,SIGNAL(readyRead()),

            this,SLOT(onSocketReadyRead()));

}

MainWindow::~MainWindow()

{

    udpSocket->abort();

    delete udpSocket;

    delete ui;

}

void MainWindow::onSocketStateChange(QAbstractSocket::SocketState socketState)

{

    switch(socketState)

    {

    case QAbstractSocket::UnconnectedState:

        LabSocketState->setText("scoket状态：UnconnectedState");

        break;

    case QAbstractSocket::HostLookupState:

        LabSocketState->setText("scoket状态：HostLookupState");

        break;

    case QAbstractSocket::ConnectingState:

        LabSocketState->setText("scoket状态：ConnectingState");

        break;

    case QAbstractSocket::ConnectedState:

        LabSocketState->setText("scoket状态：ConnectedState");

        break;

    case QAbstractSocket::BoundState:

        LabSocketState->setText("scoket状态：BoundState");

        break;

    case QAbstractSocket::ClosingState:

        LabSocketState->setText("scoket状态：ClosingState");

        break;

    case QAbstractSocket::ListeningState:

        LabSocketState->setText("scoket状态：ListeningState");

    }

}

void MainWindow::onSocketReadyRead()

{//读取数据报

    while(udpSocket->hasPendingDatagrams())

    {

        QByteArray   datagram;

        datagram.resize(udpSocket->pendingDatagramSize());

        QHostAddress    peerAddr;

        quint16 peerPort;

        udpSocket->readDatagram(datagram.data(),datagram.size(),&peerAddr,&peerPort);

        QString str=datagram.data();

        QString peer="[From "+peerAddr.toString()+":"+QString::number(peerPort)+"] ";

        ui->plainTextEdit->appendPlainText(peer+str);

    }

}

void MainWindow::on_actStart_triggered()

{//加入组播

    QString     IP=ui->comboIP->currentText();

    groupAddress=QHostAddress(IP);//多播组地址

    quint16     groupPort=ui->spinPort->value();//端口

    if (udpSocket->bind(QHostAddress::AnyIPv4, groupPort, QUdpSocket::ShareAddress))//先绑定端口

    {

        udpSocket->joinMulticastGroup(groupAddress); //加入多播组

        ui->plainTextEdit->appendPlainText("**加入组播成功");

        ui->plainTextEdit->appendPlainText("**组播地址IP："+IP);

        ui->plainTextEdit->appendPlainText("**绑定端口："+QString::number(groupPort));

        ui->actStart->setEnabled(false);

        ui->actStop->setEnabled(true);

        ui->comboIP->setEnabled(false);

    }

    else

        ui->plainTextEdit->appendPlainText("**绑定端口失败");

}

void MainWindow::on_actStop_triggered()

{//退出组播

    udpSocket->leaveMulticastGroup(groupAddress);//退出组播

    udpSocket->abort(); //解除绑定

    ui->actStart->setEnabled(true);

    ui->actStop->setEnabled(false);

    ui->comboIP->setEnabled(true);

    ui->plainTextEdit->appendPlainText("**已退出组播,解除端口绑定");

}

void MainWindow::on_actClear_triggered()

{

    ui->plainTextEdit->clear();

}

void MainWindow::on_actHostInfo_triggered()

{

    QString hostName=QHostInfo::localHostName();//本地主机名

    ui->plainTextEdit->appendPlainText("本机主机名："+hostName+"\n");

    QHostInfo   hostInfo=QHostInfo::fromName(hostName);

    QList<QHostAddress> addList=hostInfo.addresses();//

    if (!addList.isEmpty())

    for (int i=0;i<addList.count();i++)

    {

        QHostAddress aHost=addList.at(i);

        if (QAbstractSocket::IPv4Protocol==aHost.protocol())

        {

            QString IP=aHost.toString();

            ui->plainTextEdit->appendPlainText("本机IP地址："+aHost.toString());

            if (ui->comboIP->findText(IP)<0)

                ui->comboIP->addItem(IP);

        }

    }

}

void MainWindow::on_btnMulticast_clicked()

{//发送组播消息

    quint16     groupPort=ui->spinPort->value();

    QString  msg=ui->editMsg->text();

    QByteArray  datagram=msg.toUtf8();

    udpSocket->writeDatagram(datagram,groupAddress,groupPort);

    ui->plainTextEdit->appendPlainText("[multicst] "+msg);

    ui->editMsg->clear();

    ui->editMsg->setFocus();

}

三.测试结果

1. 初始状态

2.组播通讯结果