How do I not override old drawings in my iPhone app?

Question

Hi guys,

I'm trying to make a "MSPaint" app in iPhone. I am trying to use circles to draw solid circles (which i've done successfully), and then build an eraser by drawing transparent circles.

Can someone help me out here? I am kind of stuck. Thanks guys.

 #import "ImageView.h"
#import "EraseViewController.h"

@implementation ImageView

@synthesize x, y, width, height, scaling, editing, secondX, secondY, eraseX, eraseY, eraseWidth, eraseHeight;


- (id)initWithFrame:(CGRect)frame {
    if (self = [super initWithFrame:frame]) {
        newRect = CGRectMake(0,0,0,0);
        editing = false;
        scaling = false;
    }
    return self;
}



- (void)drawRect:(CGRect)rect {
    static int counter = 0;
    CGRect veryNewRect = CGRectMake(30.0, 210.0, 60.0, 60.0);
    NSLog(@"I'm being redrawn.");
    CGContextRef ref = UIGraphicsGetCurrentContext();
    if (!editing){
        if (counter == 0){
            CGContextFillEllipseInRect(ref, veryNewRect);
        }
        else{
            CGRect newRect = CGRectMake(x,y,width,height);
            CGContextFillEllipseInRect(ref, newRect);
        }   
    }
    else{
        if (counter > 1){

            CGRect eraseRect = CGRectMake(eraseX, eraseY, 15, 15);

            CGContextFillEllipseInRect(ref, eraseRect);
        }
    }

    counter++;
    NSLog(@"New value of counter is %d", counter);
}

- (void)dealloc {
    [super dealloc];
}


@end