bringSubviewToFront for CALayer

Question

I'm wondering if there is a way to bring layer on top of others layers of view. Something like bringSubviewToFront does for UIView class. I think it can be done with zPosition property of the CALayer but this means I have to check zPosition for all layers and then set proper value.

Thanks in advance.

Answer 1

I believe that the code (given that layer is your CALayer)

[layer retain];
CALayer *superlayer = layer.superlayer;
[layer removeFromSuperlayer];
[superlayer addLayer:layer];
[layer release];

will do what you want, albeit in a roundabout way.

Answer 2

It's even easier. If sublayerToBeMovedToFront is the layer you're moving and itsSuperLayer is, well, its superlayer, just say:

[itsSuperLayer addSublayer:sublayerToBeMovedToFront];

The addSublayercall simultaneously unhookssublayerToBeMovedToFront from wherever it was in the sibling list and rehooks it as the last (ie, frontmost-positioned, visually "on top") sublayer. This is exactly analogous behaviour to that of [aUIView addSubview:]

Answer 3

This category will achieve what you are talking about…

CALayer+Additions.h

#import <Foundation/Foundation.h>
#import <QuartzCore/CALayer.h>
@interface CALayer (Additions)
- (void)moveToFront;
@end

CALayer+Additions.m

#import "CALayer+Additions.h"
@implementation CALayer (Additions)
- (void)moveToFront {
    CALayer *superlayer = self.superlayer;
    [self removeFromSuperlayer];
    [superlayer addSublayer:self];
}
@end

#import "CALayer+Additions.h" within your project, and you will find a new method, moveToFront is now available to your CALayer instances.

Answer 4

If you're using CALayer for performance you should also try using only UIImageView's. In my case it turned out to be a few FPS faster. (maybe from the UIImage to CGImage conversion that I needed to perform in every image attribution)