How to see the area detected by QMouseEvent

luciole

Hello,

I have a QWidget A to which I assigned a QVBoxLayout layout, and this layout contains two widgets B and C (two QLabel). I implemented the mousePressEvent method on my parent widget A. The event seems to be triggered everywhere in a rectangle containing both B and C.

However, when I do for instance A->setStyleSheet("background-color: red"), only the background color of widgets B and C gets set to red. How can I change the background color of the whole rectangle containing B and C? From what I saw, I can't change the style of the layout itself.

Thanks!

JonB

@luciole

A->setStyleSheet("background-color: red"), only the background color of widgets B and C gets set to red

This should indeed be setting A's background to red. (No, you can't apply a style to a layout.)

luciole

But it doesn't seem to, I get this:

when putting this code inside my QWidget A:

    QVBoxLayout *layout = new QVBoxLayout;

    QLabel *text1 = new QLabel;
    QLabel *text2 = new QLabel;

    text1->setText("short text");
    text2->setText("some longer text");

    layout->addWidget(text1);
    layout->addWidget(text2);

    layout->setAlignment(text1, Qt::AlignHCenter);
    layout->setAlignment(text2, Qt::AlignHCenter);

    setLayout(layout);
    setStyleSheet("background-color: red;");

JonB

@luciole
It's supposed to work, as per e.g. https://wiki.qt.io/How_to_Change_the_Background_Color_of_QWidget, Using Style Sheet. You sure A is a QWidget, or is it actually your own class?

Bonnie

@luciole @JonB
From the OP's code, seems A is a custom widget subclassing QWidget.
So it will need some extra code in paintEvent, just as in the end of that "HowTo" you provide.

JonB

@Bonnie

From the OP's code, seems A is a custom widget subclassing QWidget.

That is what I was wondering/trying to tease out of OP. I wish people would say "It's a custom widget, let me know if that's relevant".

According to my reading, you can avoid the paintEvent subclass override, which is a bit irritating, if you want to. You need to ensure you have Q_OBJECT macro in the header of the derived class --- that's what I was going to ask the OP --- and then, I'm not certain whether needed, but I think you also need customWidget->setAttribute(Qt::WA_StyledBackground, true);. Solution at https://stackoverflow.com/a/52434565/489865 is from 2018. Read through https://stackoverflow.com/questions/7276330/qt-stylesheet-for-custom-widget, one guy claims to manage without the WA_StyledBackground, but I think the majority use it.

This question/answer may be relevant to me, I need to look at some code tomorrow where I was having this sort of trouble with background color and stylesheet....

Bonnie

@JonB
Oh, didn't know that before, glad to know there's such an attribute.
Since I also feel overriding paintEvent annoying, I've been avoiding using style sheets on custom widgets. :)

JonB

@Bonnie said in How to see the area detected by QMouseEvent:

Since I also feel overriding paintEvent annoying, I've been avoiding using style sheets on custom widgets. :)

Yeah, that's a shame limitation. I'm going to look into this for my code tomorrow, I had not appreciated you should have to do anything at all to use stylesheet on derived.

JonB

@Bonnie, @luciole
Well blow me down! This is indeed the problem/solution in my own code!

Please see my recent report of this issue in https://forum.qt.io/topic/113109/widget-background-color-at-runtime. There I have a QWidget-derived class, whose background I wish to set, which is the child widget of a QMdiSubWindow. It worked in Designer but not at runtime.

At the time I accepted @J-Hilk's reply at https://forum.qt.io/topic/113109/widget-background-color-at-runtime/2

thats a bug in Qt, you have 3 options:

upgrade to 5.12.6/7

only set stylesheets in designer

only set stylesheets in code

Edit:
found the related bug report:
https://bugreports.qt.io/browse/QTBUG-79545

Maybe there is a Qt 5.12.2 issue, but it does not seem to be my case.

Until now I had "solved" this by placing colored background not on my subclassed widget but instead on its parent, which is a QMdiSubWindow.

Instead, I now find that all I have to do is add

myDerivedWidget->setAttribute(Qt::WA_StyledBackground, true);

and the background color works at run-time!

FWIW, I tested and I do not have to have the Q_OBJECT macro on the derived class to make this work, though it does no harm. I do have to set the attribute.