Clear CGContext Lines - objective-c

Question

Once I drawn some lines over an UIImage, (like a brush application), then I want to clear them, so like a rubber. I searched a lot on this site and on Google, and I tried some codes, but I couldn't find a correct solution.
Here's the code I use to write:
- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {
if(isDrawing == YES) {
UITouch *touch = [touches anyObject];
CGPoint currentPoint = [touch locationInView:mainImageView.superview];
UIGraphicsBeginImageContext(mainImageView.frame.size);
[mainImageView.image drawInRect:CGRectMake(0, 0, mainImageView.frame.size.width, mainImageView.frame.size.height)];
CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound);
CGContextSetLineWidth(UIGraphicsGetCurrentContext(), dimension);
const CGFloat *components = CGColorGetComponents([color CGColor]);
CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), components[0], components[1], components[2], components[3]);
CGContextBeginPath(UIGraphicsGetCurrentContext());
CGContextMoveToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y);
CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), currentPoint.x, currentPoint.y);
CGContextStrokePath(UIGraphicsGetCurrentContext());
mainImageView.image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
lastPoint = currentPoint;
} else {
//Clear current line (like a rubber would do)
}
}

Answer 1

In this scenario [UIColor clearColor] won't work, use CGContextClearRect(context,rect); to clear the region!

Answer 2

Fill desired part of the context with the [UIColor clearColor].

Answer 3

The correct approach is using a Bezier path that:
records every drawings ( but actually does NOT draw.. in DrawRect we will draw.. using "stroke")
has thickness, color and so on...
draws effectively on view
Clearing it (using "removeAllPoints") and invoking setNeedsDisplay will make the background reappear.
If You want to rubber-clear the path you wrote using another tool, (say You use a pencil tool to write in blue.. and a Rubber tool to clear the blue lines and make background to reappear) you can use "containsPoint:" to remove some points form bezier path.
We did in such way.
using bezier path is NOT trivial but very exciting.. :)