A simple application with a ui form, generated in eclipse. I am working with Qt for about 6 months now, but still learning. The form is opened and shown after compiling. The form has a QWidget called "widget".

If I add the basic code to draw a qwtplot on the form it crashes. The mesage is: "QWidget: Must construct a QApplication before a QPaintDevice". I thought qapplication was constructed first in the main code, so I don't get it! I have tried linking the qwtplot to "this" and "parent" but the same result. I have also tried to move the plot from the constructor of class trygraph to a button press function but with the same result

In all examples of QwtPLot I can find the plot is made in the main function before "return a.exec();"
Appreciate any help or pointers to examples.

Qt Code: 
  1. trygraph::trygraph(QWidget *parent)
  2.     : QWidget(parent)
  3. {
  4. 	ui.setupUi(this);
  5.  
  6. 	double x[100], y1[100];
  7. 	QwtPlot *myPlot = new QwtPlot(QwtText("a Curves"), ui.widget);
  8.  
  9. 	for (int i = 0; i < 100; i++)
  10. 	{
  11. 		x[i] = i;
  12. 		y1[i] = 10-0.1*i*i;
  13. 	}
  14.  
  15. 	// add curves
  16. 	QwtPlotCurve *curve1 = new QwtPlotCurve("Curve 1");
  17.  
  18. 	// copy the data into the curves
  19. 	curve1->setData(x,y1,100);
  20.  
  21. 	curve1->attach(myPlot);
  22.  
  23. 	myPlot->replot();
  24. }
  25.  
  26. [the main function:]
  27.  
  28. int main(int argc, char *argv[])
  29. {
  30.     QApplication a(argc, argv);
  31.     trygraph w;
  32.     w.show();
  33.     return a.exec();
  34. }
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