Make a line drawn with CoreGraphics dynamic - ios

Question

I am drawing a line using the following method:
- (void)drawLineWithColor:(UIColor *)color andRect: (CGRect)rect{
if (uploadButtonHidden == 2) {
uploadPhotoButton.hidden = NO;
}
UIGraphicsBeginImageContext(rect.size);
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextTranslateCTM(context, 15, 110);
// set the stroke color and width
CGContextSetStrokeColorWithColor(context, [color CGColor]);
CGContextSetLineWidth(context, 6.0);
// move to your first point
CGContextMoveToPoint(context, 455, coords.y - 140);
// add a line to your second point
CGContextAddLineToPoint(context, coordsFinal.x, coordsFinal.y);
// tell the context to draw the stroked line
CGContextStrokePath(context);
UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
// Draw image on view
[image drawAtPoint:CGPointZero];
}
As you can see coords.y sets the starting point of my line. Is there any way when changing the coords.y point to update my line? If for example I have a method which adds 50 to coords.y every 0.5 seconds, how can I update the line without redrawing it (to prevent a memory crash)??
EDIT:
this method is called like this:
UIGraphicsBeginImageContext(self.view.frame.size);
[self drawLineWithColor:[UIColor blackColor] andRect:CGRectMake(20, 30, 1476, 1965)];
UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
imageViewForArrows = [[UIImageView alloc] initWithImage:image];
[imageArrowsArray addObject:imageViewForArrows];

Answer 1

Don't draw into an image, draw straight into the context instead. I'm assuming this method is called from within your drawRect method, in which case there will already be a value CGContextRef. You just have to get it and draw into it. Be sure to use CGContextSaveGState and CGContextRestoreGState when you apply a transform or clipping.
- (void)drawLineWithColor:(UIColor *)color andRect: (CGRect)rect{
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSaveGState(context);
CGContextTranslateCTM(context, 15, 110);
// set the stroke color and width
CGContextSetStrokeColorWithColor(context, [color CGColor]);
CGContextSetLineWidth(context, 6.0);
// move to your first point
CGContextMoveToPoint(context, 455, coords.y - 140);
// add a line to your second point
CGContextAddLineToPoint(context, coordsFinal.x, coordsFinal.y);
// tell the context to draw the stroked line
CGContextStrokePath(context);
CGContextRestoreGState(context);
}