Cannot access to QCustomPlot item.

[borasemiz]

Hello, I am new to Qt and working with QCustomPlot plotting tools and I have a problem. I cannot access the items of QCustomPlot instance from other methods in class. I don't get a compilation error, but nothing happens when I clicked the button (the method is the slot of the button). Here is the code:

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    QCustomPlot* plot = ui->widget;
    QCPItemStraightLine* line = new QCPItemStraightLine(plot);
    line->point1->setCoords(3, 5);
    line->point2->setCoords(3, 6);
    line->point1->setCoords(2,5);
    line->point2->setCoords(2,8);

    line->setPen(QPen(QColor(0, 128, 0)));
    plot->addItem(line);
}
MainWindow::~MainWindow()
{
    delete ui;
}

void MainWindow::on_pushButton_clicked()
{
    QCustomPlot* plot = ui->widget;
    if (plot->item() == 0)
        ui->label->setText("No Item");
    else
        ui->label->setText(QString::number(plot->itemCount()));
    QCPItemStraightLine* line = (QCPItemStraightLine*) plot->item(); //This statement doesn't seem to work.
    line->point1->setCoords(4, 5); // doesn't work
    line->point2->setCoords(4, 6); // doesn't work
}

When I test the item number from the method, it correctly shows me how items I have in QCustomPlot, but the last two lines doesn't work. Nothing happens. What is the problem here?

[borasemiz]

@borasemiz
I have solved it. I discovered that I needed to refresh my plot, which is to say I needed to re-plot my plot. Let me:

    //I am just skipping to the click function of my button
    QCPItemStraightLine* line = (QCPItemStraightLine) (ui->widget->item());
    
    line->point1->setCoords(5,6);
    line->point2->setCoords(5,7);
    ui->widget->replot(); //This line solved the problem.