Custom Widget not showing in layout

Pl45m4

Feels a bit weird to ask something like this, but for the sake of QWidgets, I cant get my from scratch created, custom widget (QAbstractButton base class, but own additional pImpl, which shouldn't matter) to show up in a QHBoxLayout on a plain QWidget.

Example

#include <QApplication>
#include "mywidget.h"
#include <QDebug>
#include <QHBoxLayout>
#include <QPushButton>

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

    QWidget w;
    w.setGeometry(200, 200, 500, 300);
    // dummy placeholder
    QPushButton* pb1 = new QPushButton("Click Me");
    QPushButton* pb2 = new QPushButton("Click Me");
     
    myWidget btn1;
    btn1.setObjectName("Btn1");
    // myWidget* btn1 = new myWidget;

    QHBoxLayout* hbox = new QHBoxLayout(&w);
    w.setLayout(hbox);
    hbox->addWidget(pb1); // regular QPushButton
    hbox->addWidget(&btn1); // my widget
    hbox->addWidget(pb2); // regular QPushButton

    w.show();

    // btn1.show();

    return a.exec();
}

Produces:

You can clearly see that there is some reserved space between the two default QPushButtons (where I would expect to see my widget)

The widget's paintEvent looks like this and there nothing special since it's in an early stage and doesn't do that much at all for now, except being drawn.

void myWidget::paintEvent(QPaintEvent *event)
{
    Q_UNUSED(event)

    QPainter painter(this);
    painter.setRenderHint(QPainter::Antialiasing, true);
    painter.setPen(Qt::transparent);
    painter.setBrush(QColor("#CCCCCC"));
    painter.drawRect(rect());
}

The widget itself works... I can connect the clicked signal and it shows up, when you call show() directly.

Maybe I'm missing the obvious, but I already tried everything I could think of.

btn1.show();
btn1.setVisible(true);
// ...
// ...

When widgets are shown in layouts, the paintEvent is called, right?! No other representation like QActionWidget I am missing and forgot to implement for my widget, right?
I know the answer that there isn't such thing for widgets, but I really don't know what (and why) this is happening...

Hopefully somebody can enlighten me ;-)

Christian Ehrlicher

@Pl45m4 Your custom widget has no size/sizeHint.

JoeCFD

@Pl45m4 said in Custom Widget not showing in layout:

btn1.setObjectName("Btn1");

btn1.setObjectName("Btn1"); ==> this is object name, not display name of your button.
Does your button have a name?

Pl45m4

@Christian-Ehrlicher said in Custom Widget not showing in layout:

Your custom widget has no size/sizeHint.

Aren't such things inherited from QAbstractButton?
setGeometry(0, 0, 100, 100) for example, made no difference

Added

QSize myWidget::sizeHint() const
{
     return QSize(width(), height());
}

I actually dont know if this is correct, but now I can see something at least ;-)

Is there any recommended way of implementing this? I think I just need the default behavior (like QPushButtons also have)

@JoeCFD said in Custom Widget not showing in layout:

btn1.setObjectName("Btn1"); ==> this is object name, not display name of your button.
Does your button have a name?

I know that ;-)
You can call him "Bob, the button", if you want ;-)
Just kidding, but why do you think this is relevant?

JonB

@Pl45m4 said in Custom Widget not showing in layout:

Aren't such things inherited from QAbstractButton?

QWidget::sizeHint() says

The default implementation of sizeHint() returns an invalid size if there is no layout for this widget, and returns the layout's preferred size otherwise.

and QAbstractButton says

To subclass QAbstractButton, you must reimplement at least paintEvent() to draw the button's outline and its text or pixmap. It is generally advisable to reimplement sizeHint() as well

so I think this corresponds to what you see till you add sizeHint(). I guess QPushButton does this. https://codebrowser.dev/qt5/qtbase/src/widgets/widgets/qpushbutton.cpp.html#_ZNK11QPushButton8sizeHintEv (all I have access to) shows this implementation is non-trivial!

Pl45m4

@JonB said in Custom Widget not showing in layout:

shows this implementation is non-trivial

Ok, but reasonable... It's the sum of the text (incl. font size) and the icon size if any.

To subclass QAbstractButton, you must reimplement at least paintEvent() to draw the button's outline and its text or pixmap. It is generally advisable to reimplement sizeHint() as well

Will see, maybe I move to QPushButton subclass later, since I might want to show some text and don't need the radio or tri-state functionality.

Christian Ehrlicher

@Pl45m4 said in Custom Widget not showing in layout:

setGeometry(0, 0, 100, 100) for example, made no difference

This does not do anything since the widget is in a layout.

Pl45m4

@Christian-Ehrlicher said in Custom Widget not showing in layout:

This does not do anything since the widget is in a layout.

Yep. Have seen that.
Need some fine-tuning to find the best setup for my widget, because for obvious reasons always returning QSize(width(), height()); doesn't feel like the best solution ;-)

Thanks again :)

SimonSchroeder

@Pl45m4 said in Custom Widget not showing in layout:

always returning QSize(width(), height()); doesn't feel like the best solution ;-)

I guess that QPushButton uses the actual text displayed (plus some padding) to calculate the size hint. QFontMetrics might help here.