Question

I’ve got a custom view with the following drawRect method

- (void)drawRect:(CGRect)rect
{
    CGContextRef ctx = UIGraphicsGetCurrentContext();
    float w = rect.size.width;

    CGContextSetFillColorWithColor(ctx, [UIColor blackColor].CGColor);
    CGContextAddArc(ctx, w / 2, w / 2, w / 2 - 10,  0, 2 * M_PI, 0); 
    CGContextDrawPath(ctx, kCGPathFill);

}

I’m expecting to see a black circle, however, for some reason it draws a black rectangle instead. I guess the whole view is just getting filled with black. Where is the problem?

Answer 1

Perhaps your view’s backgroundColor is also black (which is the default for opaque views)?

Also, you shouldn’t assume that the rect parameter covers the whole view, it could be only a part of the view that has been marked as needing to be redrawn. You should base your geometry calculations on the view’s bounds instead.