UIImage from CALayer in iOS

问题

In my application, I have created a CALayer (with a few sublayers - the CALayer is composed of shapes added as sublayers).

I am trying to create a UIImage that I will be able to upload to a server (I have the code for this). However, I can't figure out how to add the CALayer to a UIImage.

Is this possible?

回答1:

Sounds like you want to render your layer into a UIImage. In that case, the method below should do the trick. Just add this to your view or controller class, or create a category on CALayer.

- (UIImage *)imageFromLayer:(CALayer *)layer
{
  UIGraphicsBeginImageContextWithOptions(layer.frame.size, NO, 0);

  [layer renderInContext:UIGraphicsGetCurrentContext()];
  UIImage *outputImage = UIGraphicsGetImageFromCurrentImageContext();

  UIGraphicsEndImageContext();

  return outputImage;
}

回答2:

Todd's answer is correct, however for retina screens there should be a little difference:

- (UIImage *)imageFromLayer:(CALayer *)layer
{

    if ([[UIScreen mainScreen] respondsToSelector:@selector(scale)])
        UIGraphicsBeginImageContextWithOptions([layer frame].size, NO, [UIScreen mainScreen].scale);
    else
        UIGraphicsBeginImageContext([layer frame].size);

    [layer renderInContext:UIGraphicsGetCurrentContext()];
    UIImage *outputImage = UIGraphicsGetImageFromCurrentImageContext();

    UIGraphicsEndImageContext();

    return outputImage;
}

回答3:

I have created a Swift extension based for this:

extension UIImage {
    class func imageWithLayer(layer: CALayer) -> UIImage {
        UIGraphicsBeginImageContextWithOptions(layer.bounds.size, layer.opaque, 0.0)
        layer.renderInContext(UIGraphicsGetCurrentContext()!)
        let img = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
        return img
    }
}

The usage:

var gradient = CAGradientLayer()
gradient.colors = [UIColor.redColor().CGColor, UIColor.blueColor().CGColor]
gradient.frame = CGRect(x: 0, y: 0, width: 200, height: 200)

let image = UIImage.imageWithLayer(gradient)

回答4:

Swift 3 version with a little bit of error checking for context.

extension UIImage {
  class func image(from layer: CALayer) -> UIImage? {
    UIGraphicsBeginImageContextWithOptions(layer.bounds.size, 
  layer.isOpaque, UIScreen.main.scale)

    defer { UIGraphicsEndImageContext() }

    // Don't proceed unless we have context
    guard let context = UIGraphicsGetCurrentContext() else {
      return nil
    }

    layer.render(in: context)
    return UIGraphicsGetImageFromCurrentImageContext()
  }
}

来源：https://stackoverflow.com/questions/3454356/uiimage-from-calayer-in-ios

标签

ios

objective-c

uiimageview

uiimage

calayer