Qt serial communication does not work

[segtteee]

i wrote the code Qt serial communication qt with device through UART.
but if i preess the "connect" button, noting happened .
qt show the message
///Debugging starts
No connected device found///

How can i connect the device ? I connected cable correctly

#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <QMainWindow>
#include <QtSerialPort/QSerialPort>
#include <QMessageBox>
#include <QIODevice>
#include <QDebug>
namespace Ui {
class MainWindow;
}
class MainWindow : public QMainWindow
{
    Q_OBJECT
public:
    explicit MainWindow(QWidget *parent = 0);
    QSerialPort*serial; //plus
    QSerialPort*port;
    QWidget*main_widget;
    void readData();
    ~MainWindow();

protected:
    void sendMsg(const QString &msg);

public slots:
    void recvMsg();

private slots:
    //void readData();  //plus
    void readSerialData();

    void on_pushButton_connect_clicked();

    void on_pushButton_disconnect_clicked();


    void on_pushButton_send_clicked();

private:
    Ui::MainWindow *ui;
    QSerialPort *mSerialport;

};
#endif // MAINWINDOW_H

#include "mainwindow.h"
#include <QApplication>
#include <QSerialPort>
#include <QSerialPortInfo>
#include <QDebug>
#include <QMessageBox>
#include <QIODevice>
int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    foreach(const QSerialPortInfo &info,QSerialPortInfo::availablePorts()){

        QSerialPort serial;
        serial.setPort(info);
        if (serial.open(QIODevice::ReadWrite))
            serial.close();
    }

    MainWindow w;
    w.show();

    return a.exec();
}

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QtSerialPort/QSerialPort>
#include <QSerialPortInfo>
#include <QMessageBox>
#include <QObject>
#include <QIODevice>
#include <QDebug>
#include <QPlainTextEdit>
#include <QDateTime>
QSerialPort serial;
MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow),
    mSerialport{new QSerialPort}
{
    ui->setupUi(this);
    mSerialport->setPortName("/dev/ttyUSB0");
    mSerialport->setBaudRate(QSerialPort::Baud19200);
    mSerialport->setDataBits(QSerialPort::Data8);
    mSerialport->setParity(QSerialPort::NoParity);
    mSerialport->setStopBits(QSerialPort::OneStop);
    mSerialport->setFlowControl(QSerialPort::NoFlowControl);
    //mSerialport->open(QIODevice::ReadWrite);

    connect(this->mSerialport, SIGNAL(readyRead()), this, SLOT(readSerialData()));
    connect(this->mSerialport, SIGNAL(readyRead()), this, SLOT(recvMsg()));
    connect(ui->pushButton_send, &QPushButton::clicked, [=](){
    sendMsg(ui->textEdit->toPlainText());
    });
    //connect(serial,QSerialPort::readyRead,this,MainWindow::readData());
}
MainWindow::~MainWindow()
{
    delete mSerialport;
    delete ui;
}

void MainWindow::readSerialData()
{
    QByteArray lTmpBA;
    lTmpBA = mSerialport->readAll();

    qDebug() << "Received data: " << lTmpBA;
}



void MainWindow::on_pushButton_connect_clicked()
{

    foreach(QSerialPortInfo item, QSerialPortInfo::availablePorts()) {
        if (item.manufacturer() == "/dev/ttyUSB0") { //past your manufacturer here
            mSerialport->setPort(item);
            if(!mSerialport->open(QIODevice::ReadWrite)){
                QMessageBox::information(this, tr("connect"),
                                         "serialcommunication start");
            } else {
                QMessageBox::critical(this, tr("fail"), mSerialport->errorString());
            }
        } else {
            qDebug() << "No connected device found";
        }
    }
}

void MainWindow::on_pushButton_disconnect_clicked()
{

    QMessageBox::information(this, tr("disconnect"), "serial communication end");
    mSerialport->close();
}

void MainWindow::on_pushButton_send_clicked()
{
    mSerialport->open(QSerialPort::ReadWrite);
    mSerialport->write(ui->textEdit->toPlainText().toLatin1());

}


void MainWindow::sendMsg(const QString &msg){
      this->mSerialport->write(QByteArray::fromHex(msg.toLatin1()));
      ui->comLog->insertPlainText(QDateTime::currentDateTime().toString("yyyy-MM-dd hh:mm:ss") + " [send] " + msg + "\n");
}

void MainWindow::recvMsg(){
      QByteArray msg = this->mSerialport->readAll();
        //do something
      ui->comLog->insertPlainText(QDateTime::currentDateTime().toString("yyyy-MM-dd hh:mm:ss") + " [recieve] " + msg.toHex().data() + "\n");
}

[Moved to General and Desktop ~kshegunov]
[Locked as duplicate of https://forum.qt.io/topic/83084/qt-serial-communication-using-uart ~kshegunov]