Question

I am trying draw an random graph which display on imageview, I try this code

-(void)createGraph{
        UIGraphicsBeginImageContext(self.drawImage.frame.size);
        [drawImage.image drawInRect:CGRectMake(0, 0, drawImage.frame.size.width, drawImage.frame.size.height)];    
        CGContextRef context    = UIGraphicsGetCurrentContext();
        CGContextSetStrokeColorWithColor(context, [UIColor redColor].CGColor);
        CGContextSetLineWidth(context, 2.0);
        int i = 0;
        while (i<=20) {
            int r = rand() % 100;

            CGContextMoveToPoint(context, 20, 320);
            CGContextAddLineToPoint(context, linePoint.x+20+i*r, linePoint.y+320-i*r);         
            CGContextStrokePath(context);   
            i++;

            NSLog(@"random value %d",r);
        }
        drawImage.image = UIGraphicsGetImageFromCurrentImageContext();
    }

But its drawing a diagonal on single line. has show in below image

I am expecting to draw a graph line! using coregraphics

Answer 1

First of all, you cannot put CGContextAddLineToPoint into the loop. Remove (just) the loop, and make another loop in e.g. viewDidLoad, at each iteration, call -(void)createGraph giving the last point and the next one. Now the last point you will assign to CGContextMoveToPoint, and the next point you will give to CGContextAddLineToPoint. By the way, add CGContextBeginPath(context); right after CGContextSetLineWidth(context, 2.0);