implement paintEvent of QAbstractButton

sandro4912

I subclassed a widget from QAbstractButton which should be represented by its attached icon. However i dont see anything with my paint impkementation. I already sorted out with a QPushButton, that the ressource icon is really shown (QPushButton shows the icon).

I tryed this but it does not work:

#include "cellbutton.h"

#include <QIcon>
#include <QPainter>

CellButton::CellButton(CellButton::State state, QWidget *parent)
    :QAbstractButton{ parent },
      mHasBomb{ static_cast<bool>(state) }
{
    setFixedSize(17, 17);

    setIcon(QIcon{":ressources/cell_covered"});
}

void CellButton::paintEvent(QPaintEvent * /*event*/)
{
    QPainter painter;
    icon().paint(&painter, geometry());
}

Chris Kawa

You need to give the painter something to paint on i.e.
QPainter painter(this);
otherwise all draw calls just do nothing.

sandro4912

I updated the method to

    QPainter painter{ this };
    icon().paint(&painter, geometry());

still no icon gets painted.

SGaist

Hi,

Check that the icon is valid.

sandro4912

i did by running this in main:

    QApplication app(argc, argv);
    QPushButton button;
    button.setIcon(QIcon{":ressources/cell_covered"});
    button.show();
    return QApplication::exec();

SGaist

By the way, why not paint the image directly ?

sandro4912

i also tryed that

void CellButton::paintEvent(QPaintEvent * /*event*/)
{
    QPainter painter{ this };

    QImage image{":ressources/cell_covered"};
    qDebug() << image.isNull();
    painter.drawImage(geometry(), image);
}

to test i run main like this:

#include <QApplication>

#include "cellbutton.h"

#include <QPushButton>

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);

//    QPushButton button;
//    button.setIcon(QIcon{":ressources/cell_covered"});
//    button.show();   
    
    CellButton button(CellButton::State::empty);
    button.show();
    return QApplication::exec();
}

But nothing i only get a small empty gray window:

SGaist

What should appear ?

sandro4912

i expected this:

this has like the button 17x17 size

in qPushbutton icon it looks like this:

I also checkd the geometry like this:

void CellButton::paintEvent(QPaintEvent * /*event*/)
{
    QPainter painter{ this };

    QImage image{":ressources/cell_covered"};
    qDebug() << image.isNull();
    qDebug() << geometry().x();
    qDebug() << geometry().y();
    qDebug() << geometry().width();
    qDebug() << geometry().height();
    painter.drawImage(geometry(), image);
}

Ans it shows that it has the defined size of 17x 17.

mranger90

I still think that you're not loading the icon correctly.
Typically, an item from the resources has a prefix of ":/"
so in your case it should probably be ":/ressources/cell_covered.png"

sandro4912

i added the / but no difference. Still no display. As you can see at the top i already could load the QPushbutton without it to test.

I also throw the ressource system away for test and hard linked the image from a dir like this:

"/mnt/..../cell_uncovered.png"

Also here it shows in the Pushbutton but not in mine.

mranger90

ok, I whipped a little test as here:


CellButton::CellButton(bool state, QWidget *parent) :
      QAbstractButton {parent}
    , m_hasBomb { state }
{
    setFixedSize(64, 64);
    setIcon(QIcon{":/images/x.png"});
    connect(this, &CellButton::pressed, this, [=]() {
        setIcon(QIcon{":/images/pressed.png"});
        setFixedSize(60, 60);
    });
    connect(this, &CellButton::released, this, [=]() {
        setIcon(QIcon{":/images/x.png"});
        setFixedSize(64, 64);
    });
}

void CellButton::paintEvent(QPaintEvent *e)
{
    Q_UNUSED(e)
    QPainter painter(this);
    icon().paint(&painter, geometry());
}

This looked ok on ubuntu 19.04/Gnome, Qt 5.13.0. The png's are in a resource file under the /images directory.

here's the MainWindow used to test (note that CellButton is a QScopedPointer...


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

    m_cellButton.reset(new CellButton(true, this));
    m_cellButton->show();

    connect(m_cellButton.data(), &CellButton::clicked, this, [=]() {
        qDebug() << "Button Clicked";
    });
    setCentralWidget(m_cellButton.data());
}

sandro4912

I changed nothing from the exampel above except adding the widget into the main window and it works.

So why i couldn't see any result when i directly only show the button in the Application.

PS: Is QScopedPointer now common for all the pointer types in QMainWindow? I saw example were only the raw pointers are used.

SGaist

No it's not. The only reason to use a QScopedPointer with a widget would be that you don't want to make the widget a child of its "container".

mranger90

@sandro4912 There was no particular reason to use a scoped pointer. I'm trying to get away from using raw pointers so whenever I throw together a toy app I tend to experiment.