paintEvent problem

**di_zou** · 1st September 2009, 21:36

I am using the Qt plugin for Eclipse and I am following one of the tutorials for Qt 4.3.

I have this:

Qt Code:

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void cannonfield::setAngle(int angle)
{
	if (angle < 5)
    	angle = 5;
    if (angle > 70)
    	angle = 70;
    if (currentAngle == angle)
		return;
    currentAngle = angle;
    update();
    emit angleChanged(currentAngle);
}
 
void cannonfield::paintEvent(QPaintEvent * /* event */)
{
	QPainter painter(this);
    painter.drawText(200, 200, tr("Angle = ") + QString::number(currentAngle));
}

void cannonfield::setAngle(int angle)
{
	if (angle < 5)
    	angle = 5;
    if (angle > 70)
    	angle = 70;
    if (currentAngle == angle)
		return;
    currentAngle = angle;
    update();
    emit angleChanged(currentAngle);
}

void cannonfield::paintEvent(QPaintEvent * /* event */)
{
	QPainter painter(this);
    painter.drawText(200, 200, tr("Angle = ") + QString::number(currentAngle));
}

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setAngle is called by:

Qt Code:

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void lcdrange::on_horizontalSlider_valueChanged(int value)
{
	ui.lcdNumber->display(value);
	this->setValue(value);
	ui.cannon->setAngle(value);
}

void lcdrange::on_horizontalSlider_valueChanged(int value)
{
	ui.lcdNumber->display(value);
	this->setValue(value);
	ui.cannon->setAngle(value);
}

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The program will run. However, when it is run, nothing is displayed I am trying to get the angle value to be displayed in the "cannonfield" widget. The cannonfield widget is there, but the angle is not displayed. I put:

Qt Code:

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printf("test");

printf("test");

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into the paintEvent method and nothing is displayed in the console when I move the slider around. However, after I close the window, losts of "test"s are displayed.

Also, how does the keyword "emit" work?

Thanks.

**victor.fernandez** · 2nd September 2009, 08:30

Did you try setting a brush?

Qt Code:

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void cannonfield::paintEvent(QPaintEvent * /* event */)
{
    QPainter painter(this);
    painter.setPen(Qt::black);
    painter.setFont(font());
    painter.drawText(200, 200, tr("Angle = ") + QString::number(currentAngle));
}

void cannonfield::paintEvent(QPaintEvent * /* event */)
{
    QPainter painter(this);
    painter.setPen(Qt::black);
    painter.setFont(font());
    painter.drawText(200, 200, tr("Angle = ") + QString::number(currentAngle));
}

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You should use qDebug() instead of printf() or call fflush(stdout);

emit should work if you connected the signal to some slot and didn't forget to define the Q_OBJECT macro.

**di_zou** · 2nd September 2009, 14:47

Did not work after I set the pen. I think I don't have the signal connected to a slot correctly. I have:

Qt Code:

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connect(ui.cannon, SIGNAL(angleChanged(int)), this, SLOT(setValue(int)));

connect(ui.cannon, SIGNAL(angleChanged(int)), this, SLOT(setValue(int)));

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In the constructor of my lcdrange class. Also, where is the documentation for qDebug?

**victor.fernandez** · 2nd September 2009, 15:06

Can you post the code of your main widget as well as the full code of the cannonfield?

In the main documentation page, at the left side, under "API Reference", click "All functions". Use the search function from your browser to find it in the list. Here is the direct link.