Just demo test

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

    for(int i = 0; i < 3 ; i++){
        QLabel* l = new QLabel(QString::number(i));
        auto item = new QListWidgetItem;
        ui->listWidget->addItem(item);
        ui->listWidget->setItemWidget(item, l);
    }
}

void MainWindow::on_pushButton_clicked()
{
    // get item
    auto one =ui->listWidget->item(0);
    auto two = ui->listWidget->item(1);

    // get ui widget
    auto f = ui->listWidget->itemWidget(one);
    auto s = ui->listWidget->itemWidget(two);

    // cast real widget and update data
    QLabel* q = dynamic_cast<QLabel*>(f);
    q->setText("21");

    QLabel* w  =dynamic_cast<QLabel*>(s);
    w->setText("23");
}

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