On 04.09.2008, at 03:57, an0 wrote:
IMO, the size of a string with font attribute is an intrinsic property
determined only by the string and the font(and the layout of the
string on the view, but here let's fix the layout to one single line);
and the view used to render the attributed string should have a
reasonalby bigger size to hold the whole string. In other words, one
could have a good guess of the view size from the attributed string
size.
Well, this is programming, we try not to guess too much. It's much
better design to ask the object that actually does all the drawing to
tell you how much room it will take. Consider an NSTextFieldCell: It
can have no borders, rounded ends (in which case the distance from the
left and right edges to the actual text will be larger than that to
the top and bottom, to accomodate the half-circles), rectangular
border... If this measuring was done by string dimensions and a
reasonable guess, it'd mean if you realize field X should really have
rounded ends instead of straight ones, you'd have to change your
measuring code everywhere you do your reasonable guess.
On the other hand, the NSTextFieldCell knows how it has to be
configured, and it knows what algorithm to use for its current
appearance and content. It has to, or it wouldn't be able to draw
itself. Why duplicate this logic elsewhere? A cell is a lightweight
object intended to encapsulate text drawing, selection and editing,
and creating one and keeping it around means your drawings will be
much faster, because state and previous results of measurements can be
cached in the NSTextFieldCell for faster drawing.
That said, while Cocoa has a convenience method for drawing a string
in a rect in NSStringDrawing.h, there's none for measuring it. You
could roll your own according to this article:
http://www.zathras.de/blog-cocoa-text-system-everywhere.htm
but for best performance you'd want to cache the three text system
objects you created for this (the NSStringDrawing methods can't really
do much cacheing, though I've heard they try their best given their
lack of information), and that's what an NSTextFieldCell probably does
anyway, so why bother? Just use the cell class for your string
measuring and drawing.
Cheers,
-- Uli Kusterer
"The Witnesses of TeachText are everywhere..."
http://www.zathras.de
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