How to draw several lines of the graph in Qt using QCustomPlot

For example, in Visual Studio there is tChart and its Series property, which is responsible for drawing lines of the graph. Here is an example of this code

for (int j = 1; j < Nt - 1; j++)
  {
   for (int i = 1; i < Nt - 1; i++)
    {
       chart2->Series["" + (j + 1).ToString()]->Points->AddXY(i, wht[j][i]);
    }
  }

And draw this graph with a lot of lines.

But my task is transfering in Qt Creator(because in Qt Creator may making a lot of opportunities) This code

void MainWindow::drawdifnet(int Nt)
{
    int N=Nt;
    int N1=pow(N,2);
    QVector<double> x22(N), y22(N1); 
    int ii=0,jj=0;
    for (int j = 0; j < Nt ; j++)
            {
                for (int i = 0; i < Nt ; i++)
                {          
                    x22[jj]=i;
                    y22[ii]=wht[j][i];
                    ui->widget_2->addGraph();
                    ui->widget_2->graph(0)->setData(x22,y22);
                  ii++;
                }
                jj++;
    }
    ui->widget_2->xAxis->setLabel("OsX");
    ui->widget_2->yAxis->setLabel("OsY");
    ui->widget_2->xAxis->setRange(30,30);
    ui->widget_2->replot();
}

Doesn't work correctly. Result is the empty widget

In first I with help debugger check the QVectors data In this pictures see that my dinamic array wht[j][i] in work and loaded in QVector yy[ii]

I think the problem in the loop.

In QtCustomPlot tutorial this problem solving this code

ui->widget_2->graph(0)->setData(x,y);
ui->widget_2->graph(1)->setData(x11,y11);
ui->widget_2->graph(2)->setData(x22,y22);

But in my situation the quantity of lines is know when the program working.

How I create and assigned my array

void created(int Nt, int Nx) ///This function creating my dynamic array
{
    wht = new double *[Nt];
    for (int i = 0; i < Nt; i++)
        wht[i] = new double[Nx];
}

inline double fn(int T, double x) ///these 4 functions for my mathematical part(works good)
{
    if (x >= 0)
        return T;
    return 0;
}

inline double u0(int T, double x)
{
    return fn(T, x);
}

inline double u1(int T, double a, int xmin, double t)
{
    return fn(T, xmin - a * t);
}

inline double u2(int T, double a, int xmax, double t)
{
    return fn(T, xmax - a * t);
}


void calculatedifnet(int xmin, double hx, double ht, double a, int Nx, int Nt, int T)
//These main function.We have the empty array and in this function we fill array. Then we solve in the main loop and the fill the first indexes wht[j]
{
    for (int i = 0; i < Nt; i++)
    {
        wht[0][i] = u0(T, xmin + i*hx);//fill the second indexeswht[null][i]
    }

    for (int j = 0; j < Nt - 1; j++)//the calculated code(works right).The result writing in wht[j]
    {
        wht[j + 1][0] = u1(T, a, xmin, j*ht);
        for (int i = 1; i < Nt; i++)
        {
            double dudx = (wht[j][i] - wht[j][i - 1]) / hx;
            wht[j + 1][i] = -a * dudx * ht + wht[j][i];
        }
    }
}