How can I draw needle for dial in Qwt

[validator]

I write this code ( QwtDial *d=new QwtDial(ui.label) I create a dial but there is no needle .I look end I see that drawNeedle method is protected .How can I draw a needle for qwtdial .Please can you write sample code

[jacek]

You can set the needle using QwtDial::setNeedle() method.

[validator]

I use setNeedle Method but this method want QwtDialNeedle object but QwtDialNeedle is abstract class.How can I do this .

I write this code but I take access violation error.

ui.setupUi(this);
QwtDial *d=new QwtDial(ui.label);
d->setScaleArc(30,330);
d->setScale(100,10,60);
/*d->setOrigin(100);*/
d->setLineWidth(15);
d->setValue(5);	
d->setWrapping(false);
QwtDialNeedle * nd;
d->setNeedle(nd);

ui.setupUi(this);
QwtDial *d=new QwtDial(ui.label);
d->setScaleArc(30,330);
d->setScale(100,10,60);
/*d->setOrigin(100);*/
d->setLineWidth(15);
d->setValue(5);	
d->setWrapping(false);
QwtDialNeedle * nd;
d->setNeedle(nd);

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[jpn]

I use setNeedle Method but this method want QwtDialNeedle object but QwtDialNeedle is abstract class.How can I do this .

I write this code but I take access violation error.

QwtDialNeedle * nd;
d->setNeedle(nd);

QwtDialNeedle * nd;
d->setNeedle(nd);

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Yes, because you pass an uninitialized pointer which points to some random memory garbage. Instantiate one of QwtDialNeedle non-abstract subclasses. From the docs you'll see which classes inherit QwtDialNeedle.

[validator]

yes I examine docs but I can not understand .if you have time , can you write an example.
Thanks

[jacek]

yes I examine docs but I can not understand .

Use QwtCompassWindArrow, QwtDialSimpleNeedle or QwtCompassMagnetNeedle instead and make sure you create the needle object using new operator.

[validator]

Thank you .I did