qwt : no curve visible in simple plot

Greetings
I have been trying out qwt with a very simple application. I have not been able to get the plot to appear in the MainWindow but the curve is not visible. I am running qwt-5.2.0 with qt 4.6.2 on a FC12 linux machine. Everything compiles fine, with the plot showing with proper axis scaling. Only thing missing is the curve. The code is fairly simple, with my "myPlot" (derived from QwtPlot) class looking like the following ...

#include "myplot.h"

MyPlot::MyPlot(QWidget *gv) : QwtPlot ( gv)
{
int i ;

setTitle ("junk") ;
QwtPlotCurve *curve1 = new QwtPlotCurve("Curve 1");
curve1->attach(this);
// alloc memory for data arrays
xdata = new double [100] ;
ydata = new double [100] ;

//load up test data
for (i = 0; i < 100; i++)
{
xdata[i] = i ;
ydata[i] = i ;
}

curve1->setRawData(xdata, ydata, 100);
curve1->setPen(QPen(Qt::red, 3));
curve1->setStyle( QwtPlotCurve::Lines );
this->replot() ;

}
~
~

This is placed in a MainWindow with the following constructor for the MainWindow via

#include "mainwindow.h"
#include "ui_mainwindow.h"


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

myPlot = new MyPlot (this) ;
this->setCentralWidget (myPlot) ;

// do the replot in constructor for myPlot....
//myPlot->replot() ;
}

Thanks for any help you can provide