Making a layer structure for a drawing application

Question

Hi, In relation to question an eralier question of mine, I have tried and failed to create a class with a NSMuttableArray member variable holding CALayerRefs. Can someone please guide me on how to do that. What I want to do is basically create CALayerRefs or CGLayerRefs or whatever, push them into my layers variable, and then, when I need them, fetch, use their context and finally draw/hide/show/delete them.

I turn to you, guys, because apparently, there is few to none information on the net on working with layers and Quartz on an advanced level. Everybody uses the layers right away, no management needed, no member variables.

Thank you.

Answer 1

CALayerRef does not even exist. If you're talking about CALayer, there shouldn't be a problem. Just add them to the array.

If you mean CGLayerRefs, it is different because those are not Objective-C objects. NSArray only works with objects. If you want to put CGLayerRefs into an array, use a CFMutableArrayRef (the corresponding Core Foundation type) instead.

Answer 2

Here's some working code for custom view I wrote in few minutes, hope it helps. It creates 10 green layers, and animates them each second to different locations.

MBLineLayerDelegate *lineLayerDelegate;
@property (nonatomic, retain) NSMutableArray *ballLayers;

- (void)awakeFromNib
{
    self.ballLayers = [NSMutableArray array];
    lineLayerDelegate = [[MBLineLayerDelegate alloc] init];
    for (NSUInteger i = 0; i < 10; i++) {
        CALayer *ball = [CALayer layer];
        CGFloat x = self.bounds.size.width * (CGFloat)random()/RAND_MAX;
        CGFloat y = self.bounds.size.height * (CGFloat)random()/RAND_MAX;
        ball.frame = CGRectMake(x, y, 20, 20);
        ball.backgroundColor = [UIColor greenColor].CGColor;
        ball.delegate = lineLayerDelegate;
        [self.layer addSublayer:ball];
        [self.ballLayers addObject:ball];
    }

    [self performSelector:@selector(animateBallsToRandomLocation) withObject:nil afterDelay:0];
}

- (void)animateBallsToRandomLocation
{
    for (CALayer *layer in self.ballLayers) {
        CGFloat x = self.bounds.size.width * (CGFloat)random()/RAND_MAX;
        CGFloat y = self.bounds.size.height * (CGFloat)random()/RAND_MAX;
        layer.position = CGPointMake(x, y);
    }
    [self performSelector:@selector(animateBallsToRandomLocation) withObject:nil afterDelay:1];
}

Here's some code for CALayer's delegate that draws a line:

@interface MBLineLayerDelegate : NSObject {
}
- (void)drawLayer:(CALayer*)layer inContext:(CGContextRef)ctx;
@end

@implementation MBLineLayerDelegate

- (void)drawLayer:(CALayer*)layer inContext:(CGContextRef)context
{
        CGRect rect = layer.bounds;
        CGContextSaveGState(context);

        CGContextTranslateCTM(context, 0.0, rect.size.height);
        CGContextScaleCTM(context, 1.0, -1.0);
        CGContextSetAllowsAntialiasing(context, YES);
        CGContextSetShouldAntialias(context, YES);

        CGContextMoveToPoint(context, 0, 0);
        CGContextAddLineToPoint(context, rect.size.width, rect.size.height);

        CGContextRestoreGState(context);
}

@end