Question

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event 
{   
    mouseSwiped = NO;
    UITouch *touch = [touches anyObject];

    lastPoint = [touch locationInView:draw];
}

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event 
{
    mouseSwiped = YES;

    UITouch *touch = [touches anyObject];   
    CGPoint currentPoint = [touch locationInView:draw];

    UIGraphicsBeginImageContext(draw.frame.size);
    [draw.image drawInRect:CGRectMake(0, 0, draw.frame.size.width, draw.frame.size.height)];
    CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound); 
    CGContextSetLineWidth(UIGraphicsGetCurrentContext(), size);

    //eraser
    if (lastColor == 17){
        CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), 0, 0, 0, 0);
        CGContextSetBlendMode(UIGraphicsGetCurrentContext(), kCGBlendModeCopy);
    }

    else CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), r, g, b, a);

        CGContextBeginPath(UIGraphicsGetCurrentContext());
        CGContextMoveToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y);
        CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), currentPoint.x, currentPoint.y);
        CGContextStrokePath(UIGraphicsGetCurrentContext());
        draw.image = UIGraphicsGetImageFromCurrentImageContext();
        UIGraphicsEndImageContext();

        lastPoint = currentPoint;

        mouseMoved++;

    if (mouseMoved == 10) {
        mouseMoved = 0;
    }
}

- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event {
    //
}

Answer 1

us should check out NSUndoManager:

http://developer.apple.com/library/mac/#documentation/Cocoa/Reference/Foundation/Classes/NSUndoManager_Class/Reference/Reference.html

Sample Tutorial:

http://mobileorchard.com/new-in-iphone-30-tutorial-series-part-1-shake-to-undoredo-nsundomanager/