QT开发框架以其跨平台的优势，在全世界IT界如雷贯耳。其封装了功能齐全的各种类，大大的提高了开发者的效率。本篇内容将介绍如何使用QT 6.4.1框架开发服务器和客户端程序，让两端能够首发消息，服务端往客户端发送文件（客户端往服务器发送类似，没有实现）。

1.运行效果

 说明：首先运行同时运行客户端和服务端程序，服务绑定端口开启服务，客户端连接服务器。然后服务器和客户端互相打招呼，然后服务器给客户端发送一首唐诗。

2.关键代码：

2.1服务端代码

2.1.1 服务端主函数

#include "mainwindow.h"

#include <QApplication>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
    w.show();
    return a.exec();
}

2.1.2 QTcpServer实现类

头文件和实现：

#ifndef MYTCPSERVER_H
#define MYTCPSERVER_H

#include <QObject>
#include <QTcpServer>

class MyTcpServer : public QTcpServer
{
    Q_OBJECT
public:
    explicit MyTcpServer(QObject *parent = nullptr);
    //该函数是由框架调用
    void incomingConnection(qintptr socketDescriptor);

signals:
    void newClient(qintptr socket);

};

#endif // MYTCPSERVER_H

#include "mytcpserver.h"

MyTcpServer::MyTcpServer(QObject *parent)
    : QTcpServer{parent}
{

}

//该函数是由框架调用
void MyTcpServer::incomingConnection(qintptr socketDescriptor)
{
    emit newClient(socketDescriptor);
}

2.1.3 主窗口类

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include "MyTcpServer.h"
#include <QLabel>

QT_BEGIN_NAMESPACE
namespace Ui { class MainWindow; }
QT_END_NAMESPACE

class MainWindow : public QMainWindow
{
    Q_OBJECT

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

signals:
    void start(QString file);
    void sendMsg(QByteArray msg);

private slots:
    void on_start_clicked();

    void on_selectFile_clicked();

    void on_sendMsg_clicked();

    void on_transferFile_clicked();

private:
    Ui::MainWindow *ui;
    MyTcpServer *m_server;
    QLabel *m_status;
};
#endif // MAINWINDOW_H

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QThread>
#include <QMessageBox>
#include <QRandomGenerator>
#include <qDebug>
#include <QFileDialog>
#include <QString>
#include "sendfile.h"

//alt +回车添加自动添加头文件
MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
    , ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    ui->lineEditPort->setText("9521");
    ui->lineFile->setText("C:\\Users\\Administrator\\Desktop\\OKR设定.txt");
    ui->progressBar->setRange(0, 100);
    ui->progressBar->setValue(0);

    //创建服务器socket
    m_server = new MyTcpServer(this);
    connect(m_server, &MyTcpServer::newClient, this, [=](qintptr socket) {
        ui->textEditContent->append("检测到有新的客户端连接");
        //有新连接
        m_status->setPixmap(QPixmap(":/ok.png").scaled(20, 20));
        QThread *subThread = new QThread;
        SendFile* worker = new SendFile(socket);
        worker->moveToThread(subThread);

        //子线程工作是需要主线程给其发信号通知工作，此处用来通知子线程给客户端发送文件
        connect(this, &MainWindow::start, worker, &SendFile::working);

        connect(worker, &SendFile::done, this, [=](){
            ui->textEditContent->append("检测到客户端退出");
            //客户端断开
            m_status->setPixmap(QPixmap(":/error.png").scaled(20, 20));
            qDebug() << "销毁子线程资源";
            subThread->quit(); //通知退出
            subThread->wait(); //等任务做完
            subThread->deleteLater(); //相当于对new的对象进行delete操作
            worker->deleteLater();
        });
        //不能在子线程操作ui对象，读和写都不行，需要子线程通过信号通知ui线程间接操作ui对象
        connect(worker, &SendFile::text, this, [=](QByteArray msg){
            QVector<QColor> colors = {
                Qt::red, Qt::green, Qt::black, Qt::blue,
                Qt::darkRed, Qt::cyan, Qt::magenta
            };
            int index = QRandomGenerator::global()->bounded(colors.size());
            ui->textEditContent->setTextColor(colors.at(index));
            ui->textEditContent->append(msg);
        });
        //显示客户端发来的消息
        connect(worker, &SendFile::showRecvMsg, this, [=](QByteArray msg){
            ui->textEditContent->append("收到消息：" + msg);
        });

        //通知子线程发送一行文本
        connect(this, &MainWindow::sendMsg, worker, &SendFile::sendMsg);

        connect(worker, &SendFile::updateProgressBar, this, [=](int value){
            ui->progressBar->setValue(value);
        });

        subThread->start();
      });

    //处理状态栏,new一个QLabel，可以制定父对象，也可以不指定，因为需要把
    //它设置到状态栏中，设置后其父对象默认就是状态栏，状态栏析构后就会回收QLabel
    //不用delete
    m_status = new QLabel;
    m_status->setPixmap(QPixmap(":/error.png").scaled(20, 20));
    ui->statusbar->addWidget(new QLabel("状态："));
    ui->statusbar->addWidget(m_status);
}

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


void MainWindow::on_start_clicked()
{
    unsigned short port = ui->lineEditPort->text().toUShort();
    //绑定端口等待客户端连接,有客户端连接触发信号：[signal] void QTcpServer::newConnection()
    //QT中用于通信的QTcpSocket套接字对象不能跨线程访问
    m_server->listen(QHostAddress::Any, port);
    ui->start->setDisabled(true);
}


void MainWindow::on_selectFile_clicked()
{
    QString file = QFileDialog::getOpenFileName(this);
    if (!file.isEmpty()) {
        ui->lineFile->setText(file);
    }
}


void MainWindow::on_sendMsg_clicked()
{
   QString msg = ui->lineEditMsg->text();//.toUShort();
   emit sendMsg(msg.toUtf8());
   ui->textEditContent->append("发出消息：" + msg);
}

void MainWindow::on_transferFile_clicked()
{
    if (ui->lineFile->text().isEmpty()) {
        QMessageBox::information(this, "提示", "请选择要发送的文件");
        return;
    }
    emit start(ui->lineFile->text());
}

2.1.4 网络处理线程类

#ifndef SENDFILE_H
#define SENDFILE_H

#include <QObject>
#include <QString>
#include <QTcpSocket>
#include <QtEndian>

class SendFile : public QObject
{
    Q_OBJECT
public:
    explicit SendFile(qintptr socket, QObject *parent = nullptr);
    void working(QString file);
    void sendMsg(QByteArray msg);

signals:
    void done();
    void text(QByteArray msg);
    void showRecvMsg(QByteArray msg);
    void updateProgressBar(int value);

private:
    qintptr m_socket;
    QTcpSocket* m_tcpConn;
};

#endif // SENDFILE_H

#include "sendfile.h"
#include <QThread>
#include <QFile>
#include <qDebug>
#include <QTextCodec>

SendFile::SendFile(qintptr socket, QObject *parent)
    : QObject{parent}
{
    //传递过来了用于通信的套接字，就可以和对端通信了
    m_socket = socket;
}

void SendFile::working(QString file) {
    qDebug() << "子线程ID: " << QThread::currentThread();
    //注意：m_tcpConn的创建要在子线程中
    m_tcpConn = new QTcpSocket;
    //用文件描述符初始化m_tcpConn
    m_tcpConn->setSocketDescriptor(m_socket);

    //检测客户端断开
    connect(m_tcpConn, &QTcpSocket::disconnected, this, [=]() {
        m_tcpConn->close();
        m_tcpConn->deleteLater();
        emit done();
        qDebug() << "检测到客户端退出，我的资源也进行了销毁，再见！";
    });

    //检测客户端发来数据
    connect(m_tcpConn, &QTcpSocket::readyRead, this, [=]() {
        //接收数据并把数据发送给主线程进行显示
        QByteArray data = m_tcpConn->readAll();
        emit showRecvMsg(data);
    });

    qDebug() << "传输的文件: " << file;
    QFile opFile(file);
    bool ret = opFile.open(QFile::ReadOnly);
    if (ret) {
        emit updateProgressBar(0);
        //此处打开的是windows下的文件，windows默认是GBK编码，所以此处指定编码GBK
        QTextCodec *codec = QTextCodec::codecForName("GBK");
        qint64 fileSize = opFile.size();
        qint64 sendSize = 0;
        while (!opFile.atEnd()) {
            //自定格式发包，将发送长度转换成大端存储发送到对端
            QByteArray line = opFile.readLine();
            sendSize += line.size();
            QString strUnicode = codec->toUnicode(line);
            QByteArray utf8line = strUnicode.toUtf8();
            //以下代码写成两行比较稳定,如果写成
            //uint32_t len = qToBigEndian(utf8line.size());在某些环境转换长度就为0
            uint32_t orgLen = utf8line.size();
            uint32_t len = qToBigEndian(orgLen);
            QByteArray data((char*)&len, 4);
            data.append(utf8line);
            //发送一行数据给对端
            m_tcpConn->write(data);
            emit text(utf8line);
            emit updateProgressBar(100 * sendSize / fileSize);
            //为了减轻对端压力，休眠一会
            QThread::sleep(1);
        }
    }
    opFile.close();
}

void SendFile::sendMsg(QByteArray msg) {
    //用文件描述符初始化m_tcpConn
    m_tcpConn = new QTcpSocket;
    m_tcpConn->setSocketDescriptor(m_socket);

    //检测客户端断开
    connect(m_tcpConn, &QTcpSocket::disconnected, this, [=]() {
        m_tcpConn->close();
        m_tcpConn->deleteLater();
        emit done();
    });

    //检测客户端发来数据
    connect(m_tcpConn, &QTcpSocket::readyRead, this, [=]() {
        //接收数据并把数据发送给主线程进行显示
        QByteArray data = m_tcpConn->readAll();
        emit showRecvMsg(data);
    });

    //QT默认是UTF8编码，所以输入框是UTF8编码，此处指定编码方式为UTF8
    QTextCodec *codec = QTextCodec::codecForName("UTF8");
    QString strUnicode = codec->toUnicode(msg);
    QByteArray utf8line = strUnicode.toUtf8();
    uint32_t orgLen = utf8line.size();
    uint32_t len = qToBigEndian(orgLen);
    //拼接头：表示长度
    QByteArray data((char*)&len, 4);
    //拼接发送内容
    data.append(utf8line);
    m_tcpConn->write(data);
}

2.1.5 pro工程文件

QT       += core gui network

greaterThan(QT_MAJOR_VERSION, 4): QT += widgets
greaterThan(QT_MAJOR_VERSION, 5): QT += core5compat
CONFIG += c++17 console

# You can make your code fail to compile if it uses deprecated APIs.
# In order to do so, uncomment the following line.
#DEFINES += QT_DISABLE_DEPRECATED_BEFORE=0x060000    # disables all the APIs deprecated before Qt 6.0.0

SOURCES += \
    main.cpp \
    mainwindow.cpp \
    mytcpserver.cpp \
    sendfile.cpp

HEADERS += \
    mainwindow.h \
    mytcpserver.h \
    sendfile.h

FORMS += \
    mainwindow.ui

# Default rules for deployment.
qnx: target.path = /tmp/$${TARGET}/bin
else: unix:!android: target.path = /opt/$${TARGET}/bin
!isEmpty(target.path): INSTALLS += target

RESOURCES += \
    res.qrc

2.2客户端代码

2.2.1 主函数

#include "mainwindow.h"

#include <QApplication>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
    w.show();
    return a.exec();
}

2.2.2 主窗口类

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>

QT_BEGIN_NAMESPACE
namespace Ui { class MainWindow; }
QT_END_NAMESPACE

class MainWindow : public QMainWindow
{
    Q_OBJECT

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

signals:
    void startConnect(QString, unsigned short);
    void disConnect();
    void sendMsg(QByteArray msg);

private slots:
    void on_connServer_clicked();

    void on_sendMsg_clicked();

    void on_disconnServer_clicked();

private:
    Ui::MainWindow *ui;
};
#endif // MAINWINDOW_H

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QThread>
#include <QMessageBox>
#include <QRandomGenerator>
#include "recvfile.h"

//多线程中，主线程负责相应ui事件，创建子线程，子线程处理服务端发过来的数据
//QT中通信的套接字是不能跨线程访问的，所以客户端中用于通信的套接字是不能在
//主线程创建的，需要在子线程创建通讯套接字，主线程把ip和端口传输给子线程
//子线程new一个QTcpSocket的对象，然后子线程用这个通讯套接字接受服务端
//发过来的数据
MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
    , ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    ui->IP->setText("127.0.0.1");
    ui->port->setText("9521");
    ui->disconnServer->setDisabled(true);
    //创建子线程
    QThread *subThread = new QThread;
    //重点说明：此处new RecvFile时候不能给其指定父对象
    //否则worker移动到子线程就会不生效，谨记谨记！！！
    RecvFile* worker = new RecvFile;
    worker->moveToThread(subThread);
    connect(this, &MainWindow::startConnect, worker, &RecvFile::connectServer);
    //连接服务端成功
    connect(worker, &RecvFile::connectOk, this, [=]() {
        //QMessageBox::information(this, "提示", "成功连接了服务器");
        ui->content->append("成功连接了服务器");
        ui->disconnServer->setDisabled(false);
        ui->connServer->setDisabled(true);
    });
    connect(worker, &RecvFile::message, this, [=](QByteArray msg) {
        QVector<QColor> colors = {
            Qt::red, Qt::green, Qt::black, Qt::blue,
            Qt::darkRed, Qt::cyan, Qt::magenta
        };
        int index = QRandomGenerator::global()->bounded(colors.size());
        ui->content->setTextColor(colors.at(index));
        ui->content->append("收到消息：" + msg);
    });
    connect(worker, &RecvFile::gameOver, this, [=]() {
        qDebug() << "主线程销毁子线程";
        subThread->quit();
        subThread->wait();
        subThread->deleteLater();
        worker->deleteLater();
    });
    connect(worker, &RecvFile::disconnected, this, [=] {
        ui->content->append("与服务器断开了连接");
        ui->disconnServer->setDisabled(true);
        ui->connServer->setDisabled(false);
    });
    //断开服务器连接
    connect(this, &MainWindow::disConnect, worker, &RecvFile::disConnect);
    //给服务器发消息
    connect(this, &MainWindow::sendMsg, worker, &RecvFile::sendMsg);
    //start之后，线程仍然不能正常工作，仍然需要信号触发
    subThread->start();
    qDebug() << "主线程id：" << QThread::currentThread();
}

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


void MainWindow::on_connServer_clicked()
{
    QString ip = ui->IP->text();
    unsigned short port = ui->port->text().toUShort();
    emit startConnect(ip, port);
}

void MainWindow::on_sendMsg_clicked()
{
    QString msg = ui->msg->text();
    emit sendMsg(msg.toUtf8());
    ui->content->append("发出消息：" + msg);
}

void MainWindow::on_disconnServer_clicked()
{
    emit disConnect();
    ui->disconnServer->setDisabled(true);
    ui->connServer->setDisabled(false);
}

2.2.3 处理网络数据的子线程类

#ifndef RECVFILE_H
#define RECVFILE_H

#include <QByteArray>
#include <QObject>
#include <QTcpSocket>

class RecvFile : public QObject
{
    Q_OBJECT
public:
    explicit RecvFile(QObject *parent = nullptr);
    void connectServer(QString ip, unsigned short port);
    void dealData();
    void disConnect();
    void sendMsg(QByteArray msg);

signals:
    void connectOk();
    void message(QByteArray msg);
    void gameOver();
    void disconnected();

private:
    QTcpSocket *m_tcpScoket;
};

#endif // RECVFILE_H

#include "recvfile.h"
#include <QThread>
#include <QtEndian>

RecvFile::RecvFile(QObject *parent)
    : QObject{parent}
{

}

void RecvFile::connectServer(QString ip, unsigned short port) {
    qDebug() << "子线程ID：" << QThread::currentThread();
    m_tcpScoket = new QTcpSocket;
    //该函数是非阻塞函数，所有需要connect来注册回调,告诉我连接ok
    m_tcpScoket->connectToHost(QHostAddress(ip), port);
    connect(m_tcpScoket, &QTcpSocket::connected, this, &RecvFile::connectOk);
    //连接之后怎么怎么知道有数据到来呢，继续connect连接来通知我，槽使用匿名槽函数
    connect(m_tcpScoket, &QTcpSocket::readyRead, this, [=](){
        //QByteArray all = m_tcpScoket->readAll();
        //emit message(all);
        dealData();
        //emit gameOver();
    });
    connect(m_tcpScoket, &QTcpSocket::disconnected, this, &RecvFile::disconnected);
}

void RecvFile::dealData() {
    unsigned int totalBytes = 0;
    unsigned int recvBytes = 0;
    QByteArray block;

    if (0 == m_tcpScoket->bytesAvailable()) {
        qDebug() << "没有数据";
        return;
    }
    if (m_tcpScoket->bytesAvailable() >= sizeof(int)) {
        QByteArray head = m_tcpScoket->read(sizeof(int));
        //网络字节序转小端
        totalBytes = qFromBigEndian(*(int*)head.data());
        qDebug() << "接收数据长度：：" << totalBytes;
    }
    else {
        return;
    }
    while (totalBytes -recvBytes > 0 && m_tcpScoket->bytesAvailable()) {
        block.append(m_tcpScoket->read(totalBytes - recvBytes));
        recvBytes = block.size();
    }
    if (totalBytes == recvBytes) {
        emit message(block);
    }
    //如果还有数据继续读取
    if (m_tcpScoket->bytesAvailable() > 0) {
        dealData();
        qDebug() << "递归调用数据接收";
    }
}

void RecvFile::disConnect() {
    //关闭连接，销毁自己
    m_tcpScoket->close();
    //m_tcpScoket->deleteLater();
}

//给服务器发消息
void RecvFile::sendMsg(QByteArray msg) {
    m_tcpScoket->write(msg);
}

3.开发注意事项

（1）不能在子线程直接操作ui对象，而是通过发送信号给主线程间接操作ui对象

（2）QT处理大端和小端字节序的问题，提供了如下两组四个函数：

  组一（工作于小端机器）：  qToBigEndian  （小端转大端）  qFromBigEndian （大端转小端）
  组二（工作于大端机器）： qToLittleEndian  （大端转小端）  qFromLittleEndian （小端转大端）

其中组一用在小端机器上，组二用在大端机，简单记忆后缀是BigEndian工作在小段机器，后缀是LittleEndian工作在大端机器，工作机器刚好和后缀相反。

（3）QT有父子对象树机制来回收内存，父对象析构时会先析构子对象。

（4）多线程中，主线程负责相应ui事件，创建子线程，子线程处理服务端发过来的数据QT中通信的套接字是不能跨线程访问的，所以客户端中用于通信的套接字是不能在主线程创建的，需要在子线程创建通讯套接字，主线程把ip和端口传输给子线程子线程new一个QTcpSocket的对象，然后子线程用这个通讯套接字接受服务端发过来的数据

最后附上源码下载地址： https://download.csdn.net/download/hsy12342611/87178417