Help with stock ticker style scrolling using Core Animation - objective-c

Question

I'm looking for some guidance on the best way to implement stock ticker style right-to-left scrolling of CALayers in Core Animation on OSX. I'm pretty new to Cocoa and don't know the best way to implement this.
I have a continuous stream of news items and stock details that I turn into CALayers (made up of 1 image and a CATextLayer) and I want to animate the CALayers from right to left of my custom view.
The news and stock information is constantly updating so I would like to add 1 item at a time to the view, scroll it right to left until the right-most point of the CALayer is showing, then add another CALayer to the view and start scrolling that as well. I would like to do this dynamic updating instead of taking a big snapshot of all my data, turning it into a big horizontal CALayer and scrolling that.
I'm looking for guidance on how to achieve this sort of effect -
do I manually animate each new CALayer along a path in the view? Or should I be using CAScrollLayer to achieve this effect?
Many thanks
Glen.

Answer 1

I'd do this with Quartz Composer and put a QCView in your app. It's a lot less work than you imagine.

Answer 2

You perhaps don't need to customize anything to do this. Here self is an object of class extending UIScrollView and with a UILabel to display the text.
////
//Header
#import <UIKit/UIKit.h>
#interface TickerScrollView : UIScrollView
- (void)displayText:(NSString *)string;
- (void)clearTicker;
#property (nonatomic, retain, readwrite) UILabel *textLabel;
#end
//////
//Implementation
#implementation TickerScrollView
#synthesize textLabel;
- (id)initWithFrame:(CGRect)frame {
if ((self = [super initWithFrame:frame])) {
// Initialization code
[self setFrame: frame];
[self setBounces: NO];
[self setShowsVerticalScrollIndicator:NO];
[self setShowsHorizontalScrollIndicator:NO];
[self setBackgroundColor:[UIColor greenColor]];
[self initialiseTextLabel];
}
return self;
}
- (void)initialiseTextLabel {
textLabel = [[UILabel alloc] initWithFrame:self.bounds];
[textLabel setTextAlignment:UITextAlignmentLeft];
[textLabel setNumberOfLines:1];
[textLabel sizeToFit];
[self addSubview:textLabel];
[self setScrollEnabled:YES];
}
- (void)displayText:(NSString *)string {
[self clearTicker];
[textLabel setText:string];
[textLabel sizeToFit];
[self beginAnimation];
}
- (void)clearTicker {
[textLabel setText:#""];
[textLabel sizeToFit];
CGPoint origin = CGPointMake(0, 0);
[self setContentOffset:origin];
}
- (void)beginAnimation {
CGFloat text_width = textLabel.frame.size.width;
CGFloat display_width = self.frame.size.width;
if ( text_width > display_width ) {
CGPoint origin = CGPointMake(0, 0);
[self setContentOffset:origin];
CGPoint terminal_origin = CGPointMake(textLabel.frame.size.width - self.frame.size.width, textLabel.frame.origin.y);
float duration = (text_width - display_width)/40;
[UIView beginAnimations:nil context:NULL];
[UIView setAnimationCurve:UIViewAnimationCurveLinear];
[UIView setAnimationDelay:1.0];
[UIView setAnimationDuration:duration];
[self setContentOffset:terminal_origin];
[UIView commitAnimations];
}
}
/*
// Only override drawRect: if you perform custom drawing.
// An empty implementation adversely affects performance during animation.
- (void)drawRect:(CGRect)rect {
// Drawing code
}
*/
- (void)dealloc {
[textLabel release];
[super dealloc];
}
#end