Add text to CALayer

Question

Is it possible to add a UILabel to a CALayer without subclassing and drawing it in drawInContext:?

Thanks!

Answer 1

Add a CATextLayer as a sublayer and set the string property. That would be easiest and you can easily use a layout manager to make it very generic.

Answer 2

Just to document my approach, I did it like this in Swift 4+ :

let textlayer = CATextLayer()

textlayer.frame = CGRect(x: 20, y: 20, width: 200, height: 18)
textlayer.fontSize = 12
textlayer.alignmentMode = .center
textlayer.string = stringValue
textlayer.isWrapped = true
textlayer.truncationMode = .end
textlayer.backgroundColor = UIColor.white.cgColor
textlayer.foregroundColor = UIColor.black.cgColor

caLayer.addSublayer(textlayer) // caLayer is and instance of parent CALayer 

Answer 3

I don't think you can add a UIView subclass to a CALayer object. However if you want to draw text on a CALayer object, it can be done using the drawing functions provided in NSString UIKit additions as shown below. While my code is done in the delegate's drawLayer:inContext method, the same can be used in subclass' drawInContext: method. Is there any specific UILabel functionality that you want to leverage?

- (void) drawLayer:(CALayer *)layer inContext:(CGContextRef)ctx {
  CGContextSetFillColorWithColor(ctx, [[UIColor darkTextColor] CGColor]);

  UIGraphicsPushContext(ctx);
  /*[word drawInRect:layer.bounds 
          withFont:[UIFont systemFontOfSize:32] 
     lineBreakMode:UILineBreakModeWordWrap 
         alignment:UITextAlignmentCenter];*/

  [word drawAtPoint:CGPointMake(30.0f, 30.0f) 
           forWidth:200.0f 
           withFont:[UIFont boldSystemFontOfSize:32] 
      lineBreakMode:UILineBreakModeClip];

  UIGraphicsPopContext();
}

Answer 4

Always remember to remove previous sublayers, if you gonna add another one, to prevent duplicating views:

if let sublayers = layer.sublayers {
    for sublayer in sublayers {
        sublayer.removeFromSuperlayer()
    }
}

Answer 5

CATextLayer *label = [[CATextLayer alloc] init];
[label setFont:@"Helvetica-Bold"];
[label setFontSize:20];  
[label setFrame:validFrame];
[label setString:@"Hello"];
[label setAlignmentMode:kCAAlignmentCenter];
[label setForegroundColor:[[UIColor whiteColor] CGColor]];
[layer addSublayer:label];

[label release];

Answer 6

Your UILabel already has a CALayer behind it. If you are putting together several CALayers, you can just add the UILabel's layer as a sublayer of one of those (by using its layer property).

If it's direct text drawing in a layer that you want, the UIKit NSString additions that Deepak points to are the way to go. For an example of this in action, the Core Plot framework has a Mac / iPhone platform-independent CALayer subclass which does text rendering, CPTextLayer.