Question

I am wanting to build a small line graph that get updated when I call my setPointInGraph: method. Each time I call that, I want the graph to be updated with the point that I just added, and therefore draw a line from my last point. I see the problem in my code below, in ‘drawRect:’ that it just keeps overwriting the old path.

- (void)setPointInGraph:(float)p {

    self.point = p;
    [self setNeedsDisplay];
}


- (void)drawRect:(CGRect)rect {

    CGContextRef context = UIGraphicsGetCurrentContext();
    CGFloat maxX = CGRectGetMaxX(rect);
    CGFloat maxY = CGRectGetMaxY(rect);

    CGColorRef strokeColor = [self.lineColor CGColor];
    CGContextSetStrokeColorWithColor(context, strokeColor);
    CGContextSetLineWidth(context, self.lineWidth);
    CGContextBeginPath(context);                
    CGContextMoveToPoint(context, 0.0, maxY - maxY * self.point);
    CGContextAddLineToPoint(context, maxX * (point / count), maxY - maxY * self.point);
    CGContextStrokePath(context);

    count++;

}

How can I keep the path around (such as a property) and update it when I choose to? How can I continually add to this path not overwrite it?

Answer 1

Use UIBezierPath. You can add new segments by calling addLineToPoint.