This is a useful tutorial on how to draw to a UIImageView.
I made some changes to the code (not to say you need to): I…
- subclass UIImageView
- change drawImage.image to self.image
- added to init: self.userInteractionEnabled = YES;
- made the double-tap-to-clear a setting and added a similar setting for double-tap-to-erase
- double-tap-to-erase uses CGContextSetBlendMode(UIGraphicsGetCurrentContext(), kCGBlendModeClear); – works like an eraser (otherwise use CGContextSetBlendMode(UIGraphicsGetCurrentContext(), kCGBlendModeColor);)
- added UIColor and float setter for draw color and alpha (alpha sets self.alpha – works better than setting the stroke alpha)
- use [strokeColor setStroke]; to set the stroke color
- extracted out the context drawing into a method and call it w/ whatever the end point is (either currentPoint or lastPoint)
The result is a UIImageView subclass that takes a color and alpha and optionally either clears all or toggles erase mode w/ a double tap.