Strange border/background drawn in custom NSView

Question

I am subclassing NSView and implementing my own slider control (it is easier with NSView than NSControl I think), and thus I am implementing the "drawRect" method in that view.

I also implement "mouseDragged" method and calculate the position of the knob and then i call [self setNeedsDisplay:YES] to make the NSView subclass redraw.

The problem is that when I call [self setNeedsDisplay:YES] the NSView draws a grey background and border (looks like a rounded rect), but I do not draw this in the "drawRect" method and this border and background goes away as soon as I resize the superview.

What causes this background/border draw and how can I prevent it?

Answer 1

In your drawrect method include this line:-

     [super drawRect:rect];

Answer 2

I find that [super drawRect:rect] isn't performing well, but [super setNeedsDisplay:YES] does.

Answer 3

I found that the code from the comment:

[self.superview setNeedsDisplay:YES]

worked, but not the one in the accepted answer. Just posting this for anyone else out there looking for a solution.