使用QTcpSocket

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(1)客户端每隔10ms向服务器发送一次数字字符串，从0开始。

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include  <QTcpSocket>
#include  <QLabel>
#include <QTimer>
namespace Ui {
class MainWindow;
}

class MainWindow : public QMainWindow
{
    Q_OBJECT
private:
    QTcpSocket  *tcpClient;  //socket
    QLabel  *LabSocketState;  //状态栏显示标签

    QString getLocalIP();//获取本机IP地址
protected:
    void    closeEvent(QCloseEvent *event);
public:
    explicit MainWindow(QWidget *parent = 0);
    ~MainWindow();

private slots:
//自定义槽函数
    void    onConnected();
    void    onDisconnected();
    void    onSocketStateChange(QAbstractSocket::SocketState socketState);
    void    onSocketReadyRead();//读取socket传入的数据
//
    void on_actConnect_triggered();

    void on_actDisconnect_triggered();

    void on_actClear_triggered();

    void on_pushButton_clicked();

    void send_msg();

private:
    Ui::MainWindow *ui;
    QTimer* timer;
};

#endif // MAINWINDOW_H

关键：

QTimer* timer;

#include "mainwindow.h"
#include "ui_mainwindow.h"

#include    <QHostAddress>
#include    <QHostInfo>
#include    <QThread>
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;
}
void MainWindow::closeEvent(QCloseEvent *event)
{
    if (tcpClient->state()==QAbstractSocket::ConnectedState)
        tcpClient->disconnectFromHost();
    event->accept();
}

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);

    tcpClient=new QTcpSocket(this); //创建socket变量

    timer = new QTimer(this);
    connect(timer, SIGNAL(timeout()), this, SLOT(send_msg()));

    LabSocketState=new QLabel("Socket状态：");//状态栏标签
    LabSocketState->setMinimumWidth(250);
    ui->statusBar->addWidget(LabSocketState);

    QString localIP=getLocalIP();//本机IP
    this->setWindowTitle(this->windowTitle()+"----本机IP："+localIP);
    ui->comboServer->addItem(localIP);


    connect(tcpClient,SIGNAL(connected()),this,SLOT(onConnected()));
    connect(tcpClient,SIGNAL(disconnected()),this,SLOT(onDisconnected()));

    connect(tcpClient,SIGNAL(stateChanged(QAbstractSocket::SocketState)),
            this,SLOT(onSocketStateChange(QAbstractSocket::SocketState)));
    connect(tcpClient,SIGNAL(readyRead()),
            this,SLOT(onSocketReadyRead()));
}

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

void MainWindow::onConnected()
{ //connected()信号槽函数
    ui->plainTextEdit->appendPlainText("**已连接到服务器");
    ui->plainTextEdit->appendPlainText("**peer address:"+
                                   tcpClient->peerAddress().toString());
    ui->plainTextEdit->appendPlainText("**peer port:"+
                                   QString::number(tcpClient->peerPort()));
    ui->actConnect->setEnabled(false);
    ui->actDisconnect->setEnabled(true);
}

void MainWindow::onDisconnected()
{//disConnected()信号槽函数
    ui->plainTextEdit->appendPlainText("**已断开与服务器的连接");
    ui->actConnect->setEnabled(true);
    ui->actDisconnect->setEnabled(false);
}

void MainWindow::onSocketReadyRead()
{//readyRead()信号槽函数
    while(tcpClient->canReadLine())
        ui->plainTextEdit->appendPlainText("[in] "+tcpClient->readLine());
}

void MainWindow::onSocketStateChange(QAbstractSocket::SocketState socketState)
{//stateChange()信号槽函数
    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::on_actConnect_triggered()
{//连接到服务器
    QString     addr=ui->comboServer->currentText();
    quint16     port=ui->spinPort->value();
    tcpClient->connectToHost(addr,port);
//    tcpClient->connectToHost(QHostAddress::LocalHost,port);

    
}

void MainWindow::on_actDisconnect_triggered()
{//断开与服务器的连接
    if (tcpClient->state()==QAbstractSocket::ConnectedState)
        tcpClient->disconnectFromHost();
}

void MainWindow::on_actClear_triggered()
{
    ui->plainTextEdit->clear();
}

void MainWindow::on_pushButton_clicked()
{
    timer->start(10);
}
void MainWindow::send_msg()
{
    static int m = 0;
    QString msg = QString::number(m);

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

    QByteArray  str = msg.toUtf8();
    str.append('\n');
    tcpClient->write(str);

    m++;
}

关键：

    timer = new QTimer(this);
    connect(timer, SIGNAL(timeout()), this, SLOT(send_msg()));
void MainWindow::on_pushButton_clicked()
{
    timer->start(10);
}
void MainWindow::send_msg()
{
    static int m = 0;
    QString msg = QString::number(m);

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

    QByteArray  str = msg.toUtf8();
    str.append('\n');
    tcpClient->write(str);

    m++;
}

修改：

void MainWindow::on_pushButton_clicked()
{
    timer->start(1);
}

客户端每1ms向服务器发送一个数字，此时也可以。

如果客户端中:

    while (1)
    {
        QString msg = QString::number(1);

        //ui->plainTextEdit->appendPlainText("[out] " + msg);
        qDebug() << "[out] " + msg;
        QByteArray  str = msg.toUtf8();
        str.append('\n');
        tcpClient->write(str);
    }

不断向服务器发送信息，此时页面是卡到一点都动不了，所以需要使用多线程来处理。

 一种错误的写法：

#include "workThread.h"
#include <qapplication.h>
#include <qfiledialog.h>
#include <qdebug.h>

workThread::workThread(QTcpSocket* tcpClient,QObject *parent)
	: QThread(parent)
{
   qDebug()<<"workThread::workThread" << QThread::currentThread();
   this->tcpClient = tcpClient;
   timer = new QTimer(this);
   connect(timer, &QTimer::timeout, this, [=]() {
       ok = false;
       });
   timer->start(1000);
}

workThread::~workThread()
{
}
void workThread::run()
{
    qDebug() <<"run():" << QThread::currentThread();
    send_msg();
}
void workThread::send_msg()
{
    qDebug() <<"send_msg():" << QThread::currentThread();
    while (1)
    {
        QString msg = QString::number(1);
        if (ok == false) {
            qDebug() << "[out] " + msg;
            ok = true;
        }
        QByteArray  str = msg.toUtf8();
        str.append('\n');
        tcpClient->write(str);
    }
}

workThread::workThread QThread(0xbde160)
run(): workThread(0xc744b0)
send_msg(): workThread(0xc744b0)
QSocketNotifier: Socket notifiers cannot be enabled or disabled from another thread

QSocketNotifier: Socket notifiers cannot be enabled or disabled from another thread报错-CSDN博客

class workThread  : public QThread
{
	Q_OBJECT
signals:

public:
	workThread(QObject *parent);
	~workThread();
protected:
	void run();
private:
	QTcpSocket* tcpClient;  //socket
};

void workThread::run()
{
    qDebug() <<"run():" << QThread::currentThread();
    tcpClient = new QTcpSocket(this); //创建socket变量

}

这样写会导致：

 QObject: Cannot create children for a parent that is in a different thread.
(Parent is workThread(0xc194f0), parent's thread is QThread(0xb7f940), current thread is workThread(0xc194f0)

 关键在这句：

tcpClient = new QTcpSocket(this); //创建socket变量

this是主线程（0xb7f940）的，而当前线程是子线程(0xc194f0)。

tcpClient是子线程的(0xc194f0)。

不允许出现，父亲(this)与孩子(tcpClient)是不同线程的对象，这样的情况。

可以这样写：

void workThread::run()
{
    qDebug() <<"run():" << QThread::currentThread();
    tcpClient = new QTcpSocket; //创建socket变量
}

另一种错误写法：

void workThread::run()
{
    qDebug() <<"run():" << QThread::currentThread();
    tcpClient = new QTcpSocket; //创建socket变量
    MainWindow* window = (MainWindow*)(parent());
    connect(window, &MainWindow::connectToHost, this, &workThread::connectToHost, Qt::QueuedConnection);
    qDebug() << "......";
}
void workThread::connectToHost(QString addr, quint16 port)
{
    qDebug() << "workThread::connectToHost:" << QThread::currentThread();
    tcpClient->connectToHost(addr, port);
}

run(): workThread(0x108f510)
......
workThread::connectToHost: QThread(0x100fa30)
QObject: Cannot create children for a parent that is in a different thread.
(Parent is QTcpSocket(0x109c458), parent's thread is workThread(0x108f510), current thread is QThread(0x100fa30)

run()函数：工作线程(0x108f510)

connectToHost槽函数:主线程(0x100fa30)

有一个QObject子类对象：假设它的对象名为m。

它的parent()为QTcpSocket(0x109c458)，QTcpSocket(0x109c458)所在的线程是工作线程(0x108f510)，当前线程是主线程(0x100fa30)。

然后出现了这样的错误。

这种情况和上面的错误情况类似。

关键：

主线程中的对象m

子线程的对象n

m不可以是n的parent

n不可以是m的parent

另一种思路：

再封装一个QObject子类:

#pragma once

#include <QObject>
#include <QTcpSocket>
#include <qtimer.h>
class socket  : public QObject
{
	Q_OBJECT

public:
	socket(QObject *parent=nullptr);
	~socket();
public slots:
	void connectToHost(QString hostName, quint16 port);
	void send_msg();
private:
	QTcpSocket* tcpClient;  //socket
	QTimer* timer;
	bool ok;
};

#include "socket.h"
#include <qdebug.h>
#include <QThread>
socket::socket(QObject *parent)
	: QObject(parent)
{
    qDebug() << "socket::socket:" << QThread::currentThread();
    timer = new QTimer(this);
    tcpClient = new QTcpSocket(this); //创建socket变量
    connect(timer, &QTimer::timeout, this, [=]() {
        ok = false;
        });
    timer->start(10000);
}

socket::~socket()
{
}
void socket::connectToHost(QString addr, quint16 port)
{
    qDebug() << "socket::connectToHost:" << QThread::currentThread();
    tcpClient->connectToHost(addr, port);
}
void socket::send_msg()
{
    qDebug() <<"socket::send_msg():" << QThread::currentThread();
    while (1)
    {
        QString msg = QString::number(1);
        if (ok == false) {
            qDebug() << "[out] " + msg;
            ok = true;
        }
        QByteArray  str = msg.toUtf8();
        str.append('\n');
        tcpClient->write(str);
    }
}
void workThread::run()
{
    qDebug() <<"run():" << QThread::currentThread();
    tcp_client = new socket;
    MainWindow* window = (MainWindow*)(parent());
    connect(window, &MainWindow::connectToHost, tcp_client, &socket::connectToHost);
    qDebug() << "......";

}

这样写的话，不会出现前面的问题。

但出现了新问题，window发送了connectToHost，而tcp_client没有执行connectToHost。

因为子线程没有开启事件循环。

【QT】跨线程的信号槽（connect函数）_qt跨线程信号槽-CSDN博客

QThread::exec();

void workThread::run()
{
    qDebug() <<"run():" << QThread::currentThread();
    tcp_client = new socket;
    MainWindow* window = (MainWindow*)(parent());
    connect(window, &MainWindow::connectToHost, tcp_client, &socket::connectToHost);
    qDebug() << "......";

    QThread::exec();
}

此时主线程就可以跨线程向子线程通过信号槽发送信息啦。

思考：

connect(window, &MainWindow::connectToHost, tcp_client, &socket::connectToHost);

connectToHost槽函数在哪个线程执行，取决于tcp_client对象在哪个线程。

客户端：

多线程版本

在子线程中：每1ms向服务器发送一次数据。

（还有很多bug)

（绑定的资源文件对应这个版本）

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