Transparent QWidget/QScrollArea background style setting has no effect

Question

This question relates to

I'm asking in here because I believe the SO community might have a way to fix this behavior.

So I like to set the background color of a ScrollArea to either being transparent or to a custom background image as it will contain some banners. I got it running in the Qt Creator (Designer) already! :-):

Qt Creator sample

But when deploying the app to the simulator it won't work, the are stays gray, dark gray:

Emulator sample

Here is my layout tree:

Layout Tree

And here is the stylesheet I'm using (attached & set to the MainWindow):

QMainWindow {
    background: transparent url(:/ui/designs/images_from_android/bg_plain_empty.png) top left;
}
QWidget#centralWidget {
    background-color: transparent;
}
QPushButton {
    color: red;
    border: 1px solid green;
}
QFrame#top_header {
    background: transparent url(:/ui/designs/images_from_android/bg_title_bar_landscape.png) top left repeat-x;
}
QWidget#top_banner_scroll1,
QWidget#top_banner_scroll2 {
    background: transparent url(:/ui/designs/images_from_android/stripe_bg.png) top left repeat-x;
}

This is quite puzzling. And as Qt Designer is showing me the proper design...

Johannes Matokic · Accepted Answer · 2018-01-11 14:30:03Z

29

Use the stylesheet

QScrollArea { background: transparent; }
QScrollArea > QWidget > QWidget { background: transparent; }
QScrollArea > QWidget > QScrollBar { background: palette(base); }

To understand this lets asume a similar but simplyfied layout:

scrollarea            QScrollArea
  + scrollareaContent QWidget
      + label         QLabel

Interestingly there are two widgets with an non-transparent background. The first is the scrollarea itself (made transparent with the first line of the stylesheet).

The other one (which I didn't expect) is scrollareaContent which gets addressed with the second line. There the first QWidget is the private viewport of the QScrollArea which could not be accessed directly. The other one is the scrollareaContent. This approach should make all QScrollAreas transparent without affecting any of the other widgets.

UPDATE: I added a third line to the stylesheet which prevents the scrollbars from becoming transparent as they are also QWidgets two levels below QScrollArea.

edited Jan 11, 2018 at 14:30

answered May 10, 2013 at 12:48

Johannes Matokic

9528 silver badges15 bronze badges

Sign up to request clarification or add additional context in comments.

6 Comments

Valentin H Over a year ago

+1 Thanks! the syntax QScrollArea > QWidget > QWidget helped me setting also background-color!

anon Over a year ago

This breaks the scrollbar's colors. Jadamec's answer below seems to be correct.

kambala Over a year ago

In Qt 5.6.2 I managed to make everything but scrollbars transparent with the following (order matters!): setStyleSheet("QScrollArea > QWidget > QScrollBar { background: palette(base); }"); _graphicsView->setStyleSheet("background: transparent");

bariod Over a year ago

what's _graphicsView? @kambala

bariod Over a year ago

@isanae Apparently, by setting the background of the scrollbar to any integer, it will display the default one again. (QScrollArea > QWidget > QScrollBar { background: <any integer>; })

|

Jadamec · Accepted Answer · 2014-03-14 11:09:59Z

7

Using the following stylesheets I was able to make the scroll area transparent, while keeping the default background color for scrollbars:

scrollArea.setStyleSheet("QScrollArea {background-color:transparent;}");
scrollAreaContents.setStyleSheet("background-color:transparent;");

answered Mar 14, 2014 at 11:09

Jadamec

94311 silver badges13 bronze badges

1 Comment

anon Over a year ago

This makes the context menus black on the widget. The CSS on the contents widget (the second line) should be constrained to that widget only by using its ID (from the objectName property). If the widget is named scrollAreaContents, then it should be #scrollAreaContents { background-color:transparent; }.

Lwin Htoo Ko · Accepted Answer · 2011-03-08 09:15:05Z

4

Can you try scrollArea.setStyleSheet("background-color:transparent;"); It works for me.

answered Mar 8, 2011 at 9:15

Lwin Htoo Ko

2,4064 gold badges29 silver badges38 bronze badges

3 Comments

Sebastian Mach Over a year ago

though that will make all children transparent that have no specialized stylesheet (thoughthough one could pack the children in some other container which has the right stylesheets)

Lwin Htoo Ko Over a year ago

Yes, childern will inherit the parent's stylesheet if they don't have their own stylesheet.

David Young Over a year ago

Johannes answer works correctly without affecting all children within the scroll area.

andref · Accepted Answer · 2011-03-09 15:22:08Z

0

Shouldn't you be setting styles to QScrollArea#top_banner1 and QScrollArea#top_banner2?

You're currently selecting the viewport QWidgets and, to my experience, pure QWidgets always have transparent backgrounds and do not support styling. Thus, if the scroll area has a color, it will show through.

PS. Neat styling!

answered Mar 9, 2011 at 15:22

andref

4,50736 silver badges47 bronze badges

Collectives™ on Stack Overflow

Transparent QWidget/QScrollArea background style setting has no effect

4 Answers 4

6 Comments

1 Comment

3 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

6 Comments

1 Comment

3 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related