помогите с QCompleter QT

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

        QStandardItemModel *model=new QStandardItemModel(0,1);
        mCompleter = new QCompleter(model, this);
        ui->lineEdit->setCompleter(mCompleter);
}

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

void MainWindow::on_pushButton_clicked()
{
    QStandardItemModel *model=qobject_cast<QStandardItemModel*>(mCompleter->model());
    QStandardItem *item=new QStandardItem();
    item->setData(ui->lineEdit->text(),Qt::DisplayRole);
    model->appendRow(item);

}

void MainWindow::on_pushButton_clicked()

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

    m_model = new QStringListModel(this);
    m_model->setStringList(m_lst);
    QCompleter *completer = new QCompleter(m_model,  this);
    ui->lineEdit->setCompleter(completer);

    connect(ui->pushButton, &QPushButton::clicked, this, &MainWindow::addToCompleter);
}

void MainWindow::addToCompleter()
{
    m_lst.append(ui->lineEdit->text());
    m_model->setStringList(m_lst);
}