[Development] QWidget font settings propagation parent to child

Henry Skoglund henry at tungware.se
Wed Oct 23 21:26:51 CEST 2019

On 2019-10-23 20:49, Elvis Stansvik wrote:
> Den ons 23 okt. 2019 kl 20:18 skrev Ville Voutilainen
> <ville.voutilainen at gmail.com>:
>> On Wed, 23 Oct 2019 at 18:49, Elvis Stansvik <elvstone at gmail.com> wrote:
>>> Den ons 23 okt. 2019 16:29Henry Skoglund <henry at tungware.se> skrev:
>>>> Hi,
>>>> I use Qt Creator's excellent Form Editor, however sometimes I've noticed an inconsistency in the font settings, because I'm lazy I usually only set the font property for the top MainWindow and relying on it to "trickle down" and affect the widgets as well. Except sometimes it doesn't trickle down :-( So I wrote a test app, just a main.cpp:
>>> I don't want to be that person who always asks "why are you even doing this", but.. Why are you even doing this? :p
>>> Changing the font is normally not recommended. I think the best practice is to let the font remain as the platform plugin decided, so that the user's choice of font is respected.
>> And if the user changes their choice, should it be possible to reflect
>> that dynamically on a running application? I have no trouble coming up
>> with dozens of use cases where you want to change the font of an
>> application, or a part of its widget hierarchy.
> I believe you get that for free if you leave the font alone. At least
> my Qt applications change when I change my system font choice under
> KDE.
> Elvis
In my case, I apply the font setting as a "look and feel" or signature 
telling the user that it's an app from me. Granted, a big/complicated 
application you'll be doing all of the widget settings more or less 
explicitly anyway. This is more of a concern for me for short-lived apps 
(say 500 lines in mainwindow.cpp) that I want to churn out quickly for a 
specific reason, but nevertheless convey my signature "look and feel".

Note that the point size of the font is lost as well when the 
propagation parent to child widget fails. For example, I use a 16-point 
sized font (because many of my users are old doctors) but the default 
vanilla font that appears (in my example for Windows it's in QListWidget 
and QTableWidget ) is Tahoma 8.25-point size. So even if I can live with 
Tahoma the point size of the font needs to be almost doubled.

Also. I think this is a philosophical question, because if you look at 
the "Before w.show():" debug output in my example, all the widgets 
answers: "Yes sir, we have got your order, we'll be showing the Courier 
font when the party starts". Except that some of them don't (unless 
you're on Linux).

I mean, I could live with this if the widgets that cannot deliver would 
tell me so, i.e. if they would answer "Tahoma" instead of "Courier" when 
I ask them in the "Before w.show():" section. And the fact that I have 
to pull that grapefruit trick indicates that the widget has received the 
font change, but not completely :-(

Rgrds Henry

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