Add text to CALayer

Viewed 46117

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

Thanks!

7 Answers

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();
}

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 

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.

The answers below are fine, just make sure you add otherwise you text will be blurry:

textLayer.contentsScale = UIScreen.main.scale

Final code for Swift:

let textLayer = CATextLayer()
textLayer.frame = CGRect(x: 0, y: 0, width: 60, height: 15)
textLayer.fontSize = 12
textLayer.string = "my text"
textLayer.foregroundColor = UIColor.red.cgColor
textLayer.contentsScale = UIScreen.main.scale
Related