iphone:How to redo/undo while drawing through free hand - iphone

Question

Actually i got few samples for drawing image through free hand and i integrated as well in my application.I need additional functionalities such as undo/redo.How can i achieve this?Need help on this..I used following code.
- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {
mouseSwiped = YES;
UITouch *touch = [touches anyObject];
CGPoint currentPoint = [touch locationInView:self.view];
currentPoint.y -= 20;
UIGraphicsBeginImageContext(self.view.frame.size);
[drawImage.image drawInRect:CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height)];
CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound);
CGContextSetLineWidth(UIGraphicsGetCurrentContext(), 10.0);
CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), 1.0, 0.0, 0.0, 1.0);
CGContextBeginPath(UIGraphicsGetCurrentContext());
CGContextMoveToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y);
CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), currentPoint.x, currentPoint.y);
CGContextStrokePath(UIGraphicsGetCurrentContext());
drawImage.image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
lastPoint = currentPoint;
mouseMoved++;
if (mouseMoved == 10) {
mouseMoved = 0;
}
}

Answer 1

CGMutablePathRef path;
path = CGPathCreateMutable();
- (void)drawRect:(CGRect)rect
{
CGContextRef context = UIGraphicsGetCurrentContext();
CGPathMoveToPoint(path, NULL, previousPoint.x, previousPoint.y);
CGPathAddLineToPoint(path, NULL, lastPoint.x, lastPoint.y);
CGContextAddPath(context, path);
CGContextSetLineWidth(context, 10.0);
[[UIColor greenColor] setStroke];
CGContextDrawPath(context,kCGPathFillStroke);
}
Now you can perform Undo/Redo by path's index.

Answer 2

You can try storing all paths in an array.
When you draw a new one, add it last and draw it, when you delete - remove the last and redraw all. Keep removed in another array so you can redo actions, clear the redo array when a new path is added to the paths array.
That's the most straight-forward method I can think of.