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同样的，别忘了在.pro文件中修改

QT       += core gui network

#ifndef CHAT_H
#define CHAT_H

#include <QWidget>
#include<QTcpSocket>
namespace Ui {
class chat;
}

class chat : public QWidget
{
    Q_OBJECT

public:
    explicit chat(QTcpSocket *socket,QWidget *parent = nullptr);
    ~chat();

private slots:
    void on_sendButton_clicked();

    void on_clearButton_clicked();

    void clientReadHandler();

private:
    Ui::chat *ui;
    QTcpSocket *socket;
};

#endif // CHAT_H

#ifndef WIDGET_H
#define WIDGET_H

#include <QWidget>
#include<QTcpsocket>
#include<QHostAddress>
#include<QMessageBox>
#include "chat.h"
QT_BEGIN_NAMESPACE
namespace Ui {
class Widget;
}
QT_END_NAMESPACE

class Widget : public QWidget
{
    Q_OBJECT

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

private slots:
    void on_cancelButton_clicked();

    void on_connectButton_clicked();

private:
    Ui::Widget *ui;
    QTcpSocket *socket;
    chat *ch;
};
#endif // WIDGET_H

#include "chat.h"
#include "ui_chat.h"

chat::chat(QTcpSocket *s,QWidget *parent) :
    QWidget(parent),
    ui(new Ui::chat)
{
    ui->setupUi(this);
    socket = s;
    connect(socket,&QTcpSocket::readyRead,this,&chat::clientReadHandler);
}

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

void chat::on_sendButton_clicked()
{
    QByteArray ba;
    ba.append(ui->lineEdit->text().toLatin1());
    socket->write(ba);
}


void chat::on_clearButton_clicked()
{
    ui->lineEdit->clear();
}

void chat::clientReadHandler()
{
    ui->revlineEdit->setText(QString(socket->readAll()));
}

#include "widget.h"
#include "ui_widget.h"

Widget::Widget(QWidget *parent)
    : QWidget(parent)
    , ui(new Ui::Widget)
{
    ui->setupUi(this);
    socket = new QTcpSocket;
}

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

void Widget::on_connectButton_clicked()
{
    QString ip = ui->iplineEdit->text();
    QString port = ui->portlineEdit->text();
    qDebug() << ip;
    qDebug() << port;

    socket->connectToHost(QHostAddress(ip),port.toShort());
    connect(socket,&QTcpSocket::connected,[this]{
        QMessageBox::information(this,"Tip","连接成功");
        this->hide();
        ch = new chat(socket);
        ch->show();
    });
    connect(socket,&QTcpSocket::disconnected,[this]{
        QMessageBox::information(this,"Tip","连接失败！");
    });
}

void Widget::on_cancelButton_clicked()
{
    this->close();
}