[网络协议]（二）Qt MODBUS TCP应用学习：客户端读取服务器指定寄存器数据（详细标注）

Pro文件中加入：

QT += serialbus serialport widgets

H文件：

#ifndef MODBUSCLIENT_H
#define MODBUSCLIENT_H

#include <QMainWindow>
#include <QTimer>
#include <QModbusDataUnit> //存储接收和发送数据的类，数据类型为1bit和16bit
#include <QModbusReply> //客户端访问服务器后得到的回复（如客户端读服务器数据时包含数据信息）

//声明全局变量，存储温度数据
extern double_t wendu1;
extern double_t wendu2;
extern double_t wendu3;
extern double_t wendu4;
extern double_t wendu5;
extern double_t wendu6;
extern double_t wendu7;
extern double_t wendu8;
class QModbusClient;
class QModbusReply;

namespace Ui {
class modbusclient;
}

class modbusclient : public QMainWindow
{
    Q_OBJECT

public:
    explicit modbusclient(QWidget *parent = 0);
    ~modbusclient();

private:
    Ui::modbusclient *ui;
    QModbusClient *modbusDevice = nullptr;

private slots:
    void on_lianjie_caijiqi_clicked();
    void on_kaiqi_caijiqi_clicked();
    void readReady();
    void kaishicaiji();
};

#endif // MODBUSCLIENT_H

1、在H文件中创建QModbusClient对象 *modbusDevice。

C文件：

#include "modbusclient.h"
#include "ui_modbusclient.h"

#include <QModbusTcpClient>
#include <QDebug>

double_t wendu1;
double_t wendu2;
double_t wendu3;
double_t wendu4;
double_t wendu5;
double_t wendu6;
double_t wendu7;
double_t wendu8;

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

    //创建QModbusDevice对象
    modbusDevice = new QModbusTcpClient(this);
}

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

void modbusclient::on_kaiqi_caijiqi_clicked()
{
    kaishicaiji();
    QTimer *timer = new QTimer(this); //this 为parent类, 表示当前窗口
    connect(timer, SIGNAL(timeout()), this, SLOT(kaishicaiji())); // SLOT填入一个槽函数
    timer->start(1000); // 1000毫秒, 等于 1 秒
}

void modbusclient::on_lianjie_caijiqi_clicked()
{
    if (!modbusDevice)
        return;
    if (modbusDevice->state() != QModbusDevice::ConnectedState) {
        //处于非连接状态，进行连接
        //TCP连接,端口502，地址192.168.1.126
        modbusDevice->setConnectionParameter(QModbusDevice::NetworkPortParameter, 502);
        modbusDevice->setConnectionParameter(QModbusDevice::NetworkAddressParameter, "192.168.1.126");
        //连接超时设置，2000ms
        modbusDevice->setTimeout(2000);
        //连接失败重试连接，3次
        modbusDevice->setNumberOfRetries(3);
        //调试窗口显示连接状态
        if (modbusDevice->connectDevice()) {
            qDebug()<< "Connected!";
        }
     }
        else {
        //处在连接状态进行断开连接的操作
        modbusDevice->disconnectDevice();
    }
}

//从服务器读数据的读按钮槽方法
void modbusclient::kaishicaiji()
{
    //如果设备没有被创建就返回
    if (!modbusDevice)
        return;
    //从寄存器地址32开始连续读取8个数
    QModbusDataUnit readUnit(QModbusDataUnit::HoldingRegisters,32,8);
    if (auto *reply = modbusDevice->sendReadRequest(readUnit,1)) {
        if (!reply->isFinished())
            connect(reply, &QModbusReply::finished, this, &modbusclient::readReady);
        else
            delete reply; // broadcast replies return immediately
    }
}

//在这里读的数据
void modbusclient::readReady()
{
    //QModbusReply这个类存储了来自client的数据,sender()返回发送信号的对象的指针
    auto reply = qobject_cast<QModbusReply *>(sender());
    if (!reply)
        return;
    //数据从QModbusReply这个类的result方法中获取,也就是本程序中的reply->result()
    //判断是否出错
    if (reply->error() == QModbusDevice::NoError) {
        //读取响应数据
        const QModbusDataUnit unit = reply->result();
        //qDebug() << unit.values();
        wendu1 = unit.value(0)/10.0;
        wendu2 = unit.value(1)/10.0;
        wendu3 = unit.value(2)/10.0;
        wendu4 = unit.value(3)/10.0;
        wendu5 = unit.value(4)/10.0;
        wendu6 = unit.value(5)/10.0;
        wendu7 = unit.value(6)/10.0;
        wendu8 = unit.value(7)/10.0;
        ui->wendu_1->setNum(wendu1);
        ui->wendu_2->setNum(wendu2);
        ui->wendu_3->setNum(wendu3);
        ui->wendu_4->setNum(wendu4);
        ui->wendu_5->setNum(wendu5);
        ui->wendu_6->setNum(wendu6);
        ui->wendu_7->setNum(wendu7);
        ui->wendu_8->setNum(wendu8);
    }
    reply->deleteLater();//删除reply
}

2、在C文件中将modbusDevice赋值为QModbusTcpClient类型的对象
3、在on_lianjie_caijiqi_clicked()函数中设置TCP连接的地址、端口、超时设置和重试次数
4、利用QModbusDevice的connectDevice方法接受MODBUS网络
5、创建QModbusDataUnit数据单元
6、调用QModbusDataUnit的sendReadRequest方法读取数据

UI文件：

客户端工作时截图：