Draw a circle or sequare/rectange by mouse on qwtpolt???

[wysota]

Implement a custom QwtPlotItem that will represent your rectangle. Use a QwtPlotPicker (or QwtPicker) to allow the user to choose a rectangle. Once the selection is complete, create an instance of your plot item and place it on the plot.

[jesse_mark]

Thank Wysota,

I used QwtPlotPicker and as i read from the qwtplotpicker a selected signal we be emitted once the selection is done.

so i connected it like:

// [I]this[/I] is the MainWin
 connect(plot->picker,SIGNAL(selected(QVector<QPointF>)),this,SLOT(DrawSelection(QVector<QPointF> SelectionPoints)));

// [I]this[/I] is the MainWin
 connect(plot->picker,SIGNAL(selected(QVector<QPointF>)),this,SLOT(DrawSelection(QVector<QPointF> SelectionPoints)));

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and i have the slot on the mainwindow

void MainWin::DrawSelection(QVector<QPointF> SelectionPoints)
{
/// draw the points
}

void MainWin::DrawSelection(QVector<QPointF> SelectionPoints)
{
/// draw the points
}

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but im the single is not emitted
and when i run it can see the slot saying >>

[I]object::connect: No such slot MainWin::DrawSelection(QVector<QPointF> SelectionPoints)[/I

[I]object::connect: No such slot MainWin::DrawSelection(QVector<QPointF> SelectionPoints)[/I

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]

so can u please let me know what is the mistake im making ??

Thanks

[wysota]

I think the message is pretty much self explanatory -- you don't have a slot called "DrawSelection" in your "MainWin" class. Usually this means you either forgot the Q_OBJECT macro or you didn't declare the method as a slot.

[jesse_mark]

I do have this method in the MainWin header under

public slots:
void DrawSelection( QVector<QPointF> SelectionPoints);


and i do have other methods using them as slots and i have no problem.

but what do u exactly mean by Q_OBJECT macro ? I have have Q_OBJECT in header, but to be honest i don't really know exactly what its for .

[wysota]

Ah, I read the error message again and I noticed what was wrong. Remove the variable name from the slot signature in the connect() statement.

[jesse_mark]

Thanks the error message not there, but the signal is not triggred , after i do my selection the rect and every thing but the signal is not triggered??

OK i found in the bode example that come with the qwt library

used a picker and the selected signal

this way :

// mainwindow header 
private Q_SLOTS:
        void selected(const QPolygon &);
 
//mainwindow cpp 
...
 connect(d_picker, SIGNAL(selected(const QPolygon &)),SLOT(selected(const QPolygon &)));
....
....
void MainWindow::selected(const QPolygon & )
{
 
    qDebug()<<" I got triggred ";
   ................
}

// mainwindow header 
private Q_SLOTS:
        void selected(const QPolygon &);

//mainwindow cpp 
...
 connect(d_picker, SIGNAL(selected(const QPolygon &)),SLOT(selected(const QPolygon &)));
....
....
void MainWindow::selected(const QPolygon & )
{

    qDebug()<<" I got triggred ";
   ................
}

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this signal was triggered fine, but why the

connect(picker, SIGNAL(selected(const QVector<QPointF> &)), SLOT(DrawSelection(const QVector<QPointF> &)));
was not triggered ???

[wysota]

You probably have a Rect picker, not a Point picker machine attached to the picker.