回顾：
第一章：Qt的概述
第二章：在Ubuntu编写第一个Qt程序
第三章：Qt的字符串和字符编码
第四章：Qt的信号和槽
第五章：Qt容器窗口（父窗口）
第六章：面向对象的Qt编程
第七章：Qt设计师使用（designer）
第八章：Qt创造器的使用（qtcreator）
第九章：资源和图像
第十章：目录与定时器
第十一章：鼠标和键盘事件
第十二章：Qt数据库(sqlite)
第十三章：QT多线程(QThread)

Qt网络编程

1、网络协议层次（OSI七层）

1. 应用层
2. 表示层
3. 会话层
4. 传输层：UDP、TCP
5. 网络层：IPv4，IPv6
6. 数据链路层
7. 物理层

2、socket编程

1. TCP
2. UDP

3、Qt的socket

1. QHostAddress //IP地址
   QHostAddress ip("192.168.x.x");
QHostAddress::LocalHost //127.0.0.1,本地的环回地址
QHostAddress::Broadcast //255.255.255.255,广播地址
QHostAddress::Any //0.0.0.0,可以对应任意网卡地址
2. QAbstractSocket
   bind(ip, port);//绑定IP和端口
connectToHost(ip, port);//建立和服务器连接
disconnectFromHost();//断开连接
state(); //获取套接字状态
bytesAvailable();//获取套接字等待读取数据的字节数
   信号函数：
   connected()[signal]//连接服务器成功时发送
disconnected()[signal]//断开服务器成功时发送
error(QAbstractSocket::SocketError socketError)[signal]//网络异常时发送
readyRead() [signal] //套接字有数据到来时发送
3. QUdpSocket
   hasPendingDatagrams() //判断是否有等待读取的数据包
pendingDatagramSize() //获取等待读取数据包的大小
readDatagram() //udp读操作
writeDatagram() //udp写操作

案例：udp广播

• 发送端
  • 发送网络地址：255.255.255.255
  • 指定发送的端口：8888
  • 输入广播消息
  • 每秒发送一次广播
    SenderDialog.h

#ifndef SENDERDIALOG_H
#define SENDERDIALOG_H

#include <QDialog>
#include <QUdpSocket>
#include <QTimer>

QT_BEGIN_NAMESPACE
namespace Ui { class SenderDialog; }
QT_END_NAMESPACE

class SenderDialog : public QDialog
{
    Q_OBJECT

public:
    SenderDialog(QWidget *parent = nullptr);
    ~SenderDialog();

private slots:
    void on_pushButton_clicked();

    //timed transmission messages slot function
    void sendMessage();

private:
    Ui::SenderDialog *ui;
    QUdpSocket *udpSocket;//UDP socket
    QTimer *timer;//timer
    bool isStarted;//start or stop to broadcast
};
#endif // SENDERDIALOG_H

SenderDialog.cpp

#include "SenderDialog.h"
#include "ui_SenderDialog.h"

SenderDialog::SenderDialog(QWidget *parent)
    : QDialog(parent)
    , ui(new Ui::SenderDialog)
{
    ui->setupUi(this);
    udpSocket =  new QUdpSocket(this);
    timer = new QTimer(this);
    connect(timer, SIGNAL(timeout()), this, SLOT(sendMessage()));
    isStarted = false;
}

SenderDialog::~SenderDialog()
{
    delete ui;
}


void SenderDialog::on_pushButton_clicked()
{
    if(isStarted == false){
        isStarted = true;
        timer->start(1000);
        ui->pushButton->setText("stop to broadcast");
        ui->messageEdit->setEnabled(false);
        ui->portEdit->setEnabled(false);
    }
    else{
        isStarted = false;
        timer->stop();
        ui->pushButton->setText("start to broadcast");
        ui->messageEdit->setEnabled(true);
        ui->portEdit->setEnabled(true);
    }

}

//timed transmission messages slot function
void SenderDialog::sendMessage()
{
    //get IP and port
    QString msg = ui->messageEdit->text();
    quint16 port = ui->portEdit->text().toShort();
    //send message
    //toUtf8():QString->QByteArray(char [])
    udpSocket->writeDatagram(msg.toUtf8(), QHostAddress::Broadcast, port);
}

• 接收端
  • 指定接收端口：8888
  • bind(8888)
  • 接收广播消息并显示
    ReceiverDialog.h

#ifndef RECEIVERDIALOG_H
#define RECEIVERDIALOG_H

#include <QDialog>
#include <QUdpSocket>

QT_BEGIN_NAMESPACE
namespace Ui { class ReceiverDialog; }
QT_END_NAMESPACE

class ReceiverDialog : public QDialog
{
    Q_OBJECT

public:
    ReceiverDialog(QWidget *parent = nullptr);
    ~ReceiverDialog();

private slots:
    void on_pushButton_clicked();
    //receive message slot function
    void messageReceive();

private:
    Ui::ReceiverDialog *ui;
    QUdpSocket *udpSocket;
    quint16 port;
    bool isStarted;//start or stop receiver
};
#endif // RECEIVERDIALOG_H

ReceiverDialog.cpp

#include "ReceiverDialog.h"
#include "ui_ReceiverDialog.h"

ReceiverDialog::ReceiverDialog(QWidget *parent)
    : QDialog(parent)
    , ui(new Ui::ReceiverDialog)
{
    ui->setupUi(this);
    udpSocket = new QUdpSocket(this);
    isStarted = false;
}

ReceiverDialog::~ReceiverDialog()
{
    delete ui;
}


void ReceiverDialog::on_pushButton_clicked()
{
    if(isStarted == false){
        isStarted = true;
        //get prot
        port = ui->lineEdit->text().toShort();
        //bind prot
        udpSocket->bind(port);
        //when the port has message, send readyRead signal
        connect(udpSocket, SIGNAL(readyRead()), this, SLOT(messageReceive()));
        ui->lineEdit->setEnabled(false);
        ui->pushButton->setText("stop receive");
    }
    else{
        isStarted = false;
        udpSocket->close();
        ui->lineEdit->setEnabled(true);
        ui->pushButton->setText("start receive");
    }
}

//receive message slot function
void ReceiverDialog::messageReceive()
{
    //adjust has data come now
    if(udpSocket->hasPendingDatagrams()){
        //ready to receive data from buffer
        QByteArray buffer;
        buffer.resize(udpSocket->pendingDatagramSize());
        udpSocket->readDatagram(buffer.data(), buffer.size());

        ui->listWidget->addItem(buffer);
        ui->listWidget->scrollToBottom();
    }
}

4. QTcpSocket、QTcpServer
   //有客户端和服务器连接时发送
   void QTcpServer::newConnection() [signal]
   //获取和客户端通信的套接字
   QTcpSocket *QTcpServer::nextPendingConnection()

案例：网络聊天室

• 服务器
  • 使用QTcpServer创建Tcp服务器
  • 获取、保存与客户端通信的套接字
  • 接收客户端发送的消息
  • 转发消息给其他客户端
    mkdir NetChat
    工程名：Server
    ServerDialog.h

#ifndef SERVERDIALOG_H
#define SERVERDIALOG_H

#include <QDialog>
#include <QTcpServer>
#include <QTcpSocket>
#include <QDebug>

QT_BEGIN_NAMESPACE
namespace Ui { class ServerDialog; }
QT_END_NAMESPACE

class ServerDialog : public QDialog
{
    Q_OBJECT

public:
    ServerDialog(QWidget *parent = nullptr);
    ~ServerDialog();

private slots:
	//创建服务器按钮对应的槽函数
    void on_pushButton_clicked();
    //当有客户端服务器连接时执行的槽函数
    void onNewConnect(void);
    //当有客户端给服务器发送聊天信息时执行的槽函数 
    void onReadyRead(void);

private:
	//转发聊天信息给所有在线的客户端
    void sendMessage(const QByteArray& msg);

private:
    Ui::ServerDialog *ui;
    QTcpServer server;//服务器对象
    quint16 port;//服务器端口
    //容器：保存所有和客户端通信的套接字
    QList<QTcpSocket*> tcpClientlist;
};
#endif // SERVERDIALOG_H

ServerDialog.cpp

#include "ServerDialog.h"
#include "ui_ServerDialog.h"

ServerDialog::ServerDialog(QWidget *parent)
    : QDialog(parent)
    , ui(new Ui::ServerDialog)
{
    ui->setupUi(this);
    //当有客户端和服务器连接时，发送信号newConnection
    connect(&server, SIGNAL(newConnection()), this, SLOT(onNewConnect()));
}

ServerDialog::~ServerDialog()
{
    delete ui;
}


void ServerDialog::on_pushButton_clicked()
{
	//获取端口号
    port = ui->lineEdit->text().toShort();
    //设置监听IP和端口
    bool res = server.listen(QHostAddress::Any, port);
    if(res == true){
        qDebug("create server success!");
    }
    else{
        qDebug("create server fail!");
        return;
    }
    //禁用创建服务器按钮和端口输入
    ui->pushButton->setEnabled(false);
    ui->lineEdit->setEnabled(false);
}
//当有客户端服务器连接时执行的槽函数
void ServerDialog::onNewConnect(void)
{
	//获取和客户端通信的套接字
    QTcpSocket* tcpClientSocket = server.nextPendingConnection();
    //保存套接字到容器
    tcpClientlist.append(tcpClientSocket);
    //当客户端给服务端发送信息时，发送readyRead
    connect(tcpClientSocket, SIGNAL(readyRead()), this, SLOT(onReadyRead()));
}
//当有客户端服务器连接时执行的槽函数
void ServerDialog::onReadyRead(void)
{
	//检查容器中的套接字是否已经断开
    for(int i=0;i<tcpClientlist.size();i++){
        if(tcpClientlist.at(i)->state() == QAbstractSocket::UnconnectedState){
        	//剔除失效的套接字
            tcpClientlist.removeAt(i);
        }
    }
    for(int i=0;i<tcpClientlist.size();i++){
    	//byteAvailable():获取当前套接字等待读取信息的字节数
        if(tcpClientlist.at(i)->bytesAvailable()>0){
        	//读取信息
            QByteArray readBuf = tcpClientlist.at(i)->readAll();
            //显示
            ui->listWidget->addItem(readBuf);
            ui->listWidget->scrollToBottom();
            //转发消息给其他在线客户端
            sendMessage(readBuf);
        }
    }
}

//转发聊天消息给所有在线的客户端
void ServerDialog::sendMessage(const QByteArray& msg)
{
    for(int i=0;i<tcpClientlist.size();i++){
        tcpClientlist.at(i)->write(msg);
        qDebug() << "send message:" << msg;
    }
}

• 客户端
  • 使用QTcpSocket建立和服务器的连接
  • 获取输入的聊天消息发送到服务器
  • 接收和显示服务器转发的聊天消息
    工程名：Client
    ClientDialog.h

#ifndef CLIENTDIALOG_H
#define CLIENTDIALOG_H

#include <QDialog>
#include <QTcpSocket>
#include <QMessageBox>
#include <QHostAddress>

QT_BEGIN_NAMESPACE
namespace Ui { class ClientDialog; }
QT_END_NAMESPACE

class ClientDialog : public QDialog
{
    Q_OBJECT

public:
    ClientDialog(QWidget *parent = nullptr);
    ~ClientDialog();

private slots:
    //连接服务器按钮对应的槽函数
    void on_ConnectButton_clicked();
    //发送消息按钮对应的槽函数
    void on_sendButton_clicked();
    //和服务器连接成功时执行的槽函数
    void onConnected(void);
    //和服务器断开连接时执行的槽函数
    void onDisConnected(void);
    //接收聊天服务器转发的聊天消息
    void onReadyRead(void);
    //连接服务器按钮对应的槽函数
    void onError(QAbstractSocket::SocketError);

private:
    Ui::ClientDialog *ui;
    bool status;//标记连接状态：在线/离线
    QTcpSocket tcpSocket;//和服务器通信的套接字
    QHostAddress serverIp;//服务器IP
    quint16 serverPort;//服务器端口
    QString username;//聊天昵称
};
#endif // CLIENTDIALOG_H

ClientDialog.cpp

#include "ClientDialog.h"
#include "ui_ClientDialog.h"

ClientDialog::ClientDialog(QWidget *parent)
    : QDialog(parent)
    , ui(new Ui::ClientDialog)
{
    ui->setupUi(this);
    status = false;//离线
    //和服务器连接时发送信号connected
    connect(&tcpSocket, SIGNAL(connected()), this, SLOT(onConnected()));
    //和服务器断开连接时发送信号disconnected
    connect(&tcpSocket, SIGNAL(disconnected()), this, SLOT(onDisConnected()));
    //收到信息时，发送信号readyRead()
    connect(&tcpSocket, SIGNAL(readyRead()), this, SLOT(onReadyRead()));
    //网络异常时发送信号Error
    connect(&tcpSocket, SIGNAL(error(QAbstractSocket::SocketError)), this, SLOT(onError(QAbstractSocket::SocketError)));
}

ClientDialog::~ClientDialog()
{
    delete ui;
}

//
void ClientDialog::on_ConnectButton_clicked()
{
    if(status == false){
        //建立连接
        //获取服务器ip
        QString ip = ui->serverIpEdit->text();
        if(serverIp.setAddress(ip)==false){
            QMessageBox::critical(this, "Error", "IP is error!");
            return;
        }
        //获取服务器端口
        serverPort = ui->serverPortEdit->text().toShort();
        if(serverPort < 1024 || serverPort > 48000){
            QMessageBox::critical(this, "Error", "Port is error!");
            return;
        }
        //获取聊天昵称
        username = ui->usernameEdit->text();
        if(username == ""){
            QMessageBox::critical(this, "Error", "Username is null!");
            return;
        }
        //向服务器发送连接请求
        //成功时发送信号：connected
        //失败时发送信号：disconnected
        tcpSocket.connectToHost(serverIp,serverPort);
        //标记连接状态：在线
        status = true;
    }
    else{
        //断开连接
        //向服务器发送离开聊天室的提示
        QString msg = username + ":" + "check out the chat!";
        tcpSocket.write(msg.toUtf8());
        //关闭当前通信
        //断开连接时发送信号：disconnected
        tcpSocket.disconnectFromHost();
        //标记链接而状态：离线
        status = false;
    }
}

//
void ClientDialog::on_sendButton_clicked()
{
    //获取输入的聊天信息
    QString msg = ui->messageEdit->text();
    msg = username + ":" + msg;
    tcpSocket.write(msg.toUtf8());
    //清空信息输入
    ui->messageEdit->clear();
}

//
void ClientDialog::onConnected(void)
{
    //使能发送消息按钮
    ui->sendButton->setEnabled(true);
    //禁用ip port username
    ui->serverIpEdit->setEnabled(false);
    ui->serverPortEdit->setEnabled(false);
    ui->usernameEdit->setEnabled(false);
    //按钮文本修改：离开聊天室
    ui->ConnectButton->setText("chack out");

    //向服务器发送进入聊天室提示
    QString msg = username+":"+"check in the chat!";
    //发送信息
    tcpSocket.write(msg.toUtf8());
}
//
void ClientDialog::onDisConnected(void)
{
    //禁用相关组件
    ui->sendButton->setEnabled(false);
    ui->serverIpEdit->setEnabled(true);
    ui->serverPortEdit->setEnabled(true);
    ui->usernameEdit->setEnabled(true);
    //按钮文本修改：连接服务器
    ui->ConnectButton->setText("connect to server");
}
//
void ClientDialog::onReadyRead(void)
{
    if(tcpSocket.bytesAvailable() > 0){
        QByteArray readBuf;
        readBuf.resize(tcpSocket.bytesAvailable());
        //读取聊天信息
        tcpSocket.read(readBuf.data(), readBuf.size());
        //显示聊天信息
        ui->listWidget->addItem(readBuf);
        ui->listWidget->scrollToBottom();
    }
}
//
void ClientDialog::onError(QAbstractSocket::SocketError)
{
    QMessageBox::critical(this, "Error", tcpSocket.errorString());
}