问题描述
我得到一个QWidget的默认字体的家庭使用font()。family()。我比较这与QStringList我从QFontDatabase()。families()。默认字体的家庭是Sans,但我不能在从QFontDatabase获得的列表中,我只能找到Sans Serif,Droid Sans,FreeSans等。如何QWidget的默认字体是甚至不存在的系统的字体?
这是一个经典之旅。
QFont
是字体的请求。它可能由不匹配所请求的东西满足。 实际字体可从 QFontInfo
获得。
可以在 QFont
中放置任何。在什么时候应该 QFont
更改本身以指示实际选择的字体?如果你在一个小部件上设置一个字体,然后读回它,它被改变,以匹配什么字体在那里是相当困惑。所以,没有这样的合理点,其中 QFont
可以变形,因此 QFont
不能只是一个请求。 / p>
您控制 QFont
,但系统的字体可用性和其他约束控制匹配 QFontInfo
。
不变量可以表示为:
QFontDatabase db;
QFont const font = widget-> font();
QStringList const families = db.families();
Q_ASSERT(families.contains(font.family())|| true);
QFontInfo const info(font);
Q_ASSERT(families.contains(info.family()));
I'm getting a QWidget's default font's family using font().family(). I compare this against the QStringList I get from QFontDatabase().families(). The default font's family is "Sans" but I cannot find that in the list I get from QFontDatabase, I can only find Sans Serif, Droid Sans, FreeSans etc. How come QWidget's default font is something that is not even present on the system's fonts?
This is a classic trip-up.
Logically, QFont
is a request for a font. It may be satisfied by something that doesn't quite match what was requested. The actual font is available from QFontInfo
.
If you think about it, you can put "whatever" in a QFont
. At what point should QFont
change itself to indicate what font was actually selected? It'd be rather baffling if you set a font on a widget, then read it back, and it got changed to match what fonts are there. So, there's no such reasonable point where a QFont
could morph, so QFont
can't be but a request.
You control QFont
, but the system's font availability and other constraints controls the matching QFontInfo
.
The invariant may be expressed as:
QFontDatabase db;
QFont const font = widget->font();
QStringList const families = db.families();
Q_ASSERT(families.contains(font.family()) || true);
QFontInfo const info(font);
Q_ASSERT(families.contains(info.family()));
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