Mac Forum / Programming / Mac Programming / March 2008

In article
<79d3e4eb-b1f1-4fc9-ac43-d1da8b39c4ea@t54g2000hsg.googlegroups.com>,

Text is complicated. There are Unicode and kerning rules that will have
you tearing your hair. Better just to re-use the existing Cocoa classes
for drawing scrolling text.

For you, I've built a simple working model of the ticker tape view you
asked for here: http://www.TurboZen.com/sourcecode/Ticker.zip

It is built out of an NSTextView, with the following tricks:
The animation is driven by a timer, that fires 60 times a second,
executing this:

- (void)step:(NSTimer *)timer {
 mOffset -= 2; // pixels per tick
 [self setTextContainerInset:NSMakeSize(mOffset, 0)];
 [self setNeedsDisplay:YES];
}

Limitations:

* the timer is created scheduled, on the runloop in the default mode. To
get the ticker to work while the user is tracking a menu or a control,
you need to add the timer to the other runloop modes.

* I didn't add any API to set the font attributes, such as color of the
appended text.

* A real program would use the NSTextContainer owned by the NSTextView
to measure the pixels in the string prefix, delete the prefix, and reset
the container offset, so you wouldn't waste storage storing dead history
in the prefix of the string of the NSTextStorage.

(If you are new to Cocoa, you may miss that much of the creation and
wiring up of the objects in a program is specified in Interface Builder,
in the .nib file. That is how the AppDelegate and gets created and how
it gets a pointer to the TickerView.)

See
file:///Developer/ADC%20Reference%20Library/documentation/Cocoa/Conceptua
l/TextArchitecture/index.html for more information.

On 28/03/2008, flopbucket wrote in message <79d3e4eb-b1f1-4fc9-ac43-
d1da8b39c4ea@t54g2000hsg.googlegroups.com>:

That's very oldschool.  There are better ways now.

In Cocoa, you will be writing your text to an NSTextView.

NSTextView inherits from NSView.

NSViews have two properties called 'frame' and 'bounds'.  Once controls
where the view appears in the view that contains it.  The other controls
where the contents of the view are drawn in relation to its boundaries.
Normally they're the same but a good way to scroll content is to mess with
one, while leaving the other static.

I think one way to scroll your content (the text in an NSTextView) would
be to use setBounds continually.  Take a look at the documentation for
NSView, and the conceptual doc here:

<http://developer.apple.com/documentation/Cocoa/Conceptual/CocoaViewsGuide/
Coordinates/chapter_3_section_3.html>

Since you're relatively new to Cocoa I would suggest you handle your own
scrolling, because it will give you a good idea how Cocoa objects behave.
But once you understand what's happening you might like to know that Cocoa
has an animation class especially designed for animating views:

<http://developer.apple.com/documentation/Cocoa/Conceptual/AnimationGuide/A
rticles/ViewAnimations.html>

Simon.