objective-c: draw line on top of UIImage or UIImageView - objective-c

Question

How do I draw a simple line on top of a UIImage or UIImageView?

Answer 1

The following code works by creating a new image the same size as the original, drawing a copy of the original image onto the new image, then drawing a 1 pixel line along to the top of the new image.
// UIImage *originalImage = <the image you want to add a line to>
// UIColor *lineColor = <the color of the line>
UIGraphicsBeginImageContext(originalImage.size);
// Pass 1: Draw the original image as the background
[originalImage drawAtPoint:CGPointMake(0,0)];
// Pass 2: Draw the line on top of original image
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetLineWidth(context, 1.0);
CGContextMoveToPoint(context, 0, 0);
CGContextAddLineToPoint(context, originalImage.size.width, 0);
CGContextSetStrokeColorWithColor(context, [lineColor CGColor]);
CGContextStrokePath(context);
// Create new image
UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
// Tidy up
UIGraphicsEndImageContext();
Alternatively, you could create the line as a CAShapeLayer then add it as a subview to the UIImageView (see this answer).

Answer 2

For Swift 3.0
UIGraphicsBeginImageContext(originalImage.size)
originalImage.draw(at: CGPoint(x: 0, y: 0))
let context = UIGraphicsGetCurrentContext()!
context.setLineWidth(2)
context.move(to: CGPoint(x: 0, y: originalImage.size.height - 2))
context.addLine(to: CGPoint(x: originalImage.size.width, y: originalImage.size.height - 2))
context.setStrokeColor(UIColor.red.cgColor)
context.strokePath()
let finalImage = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()

Answer 3

For Swift 2.3
func drawLineOnImage(size: CGSize, image: UIImage, from: CGPoint, to: CGPoint) -> UIImage {
UIGraphicsBeginImageContext(size)
image.drawAtPoint(CGPointZero)
let context = UIGraphicsGetCurrentContext()
CGContextSetLineWidth(context, 1.0)
CGContextSetStrokeColorWithColor(context, UIColor.blueColor().CGColor)
CGContextMoveToPoint(context, from.x, from.y)
CGContextAddLineToPoint(context, to.x, to.y)
CGContextStrokePath(context)
let resultImage = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()
return resultImage
}