Question

Cocoa’s NSScrollView is horribly under-explained. I hope someone here knows what it’s all about and can spare me a few seconds.

So I have a custom NSView. I implement -drawRect: for it to draw something, fill itself with colour, whatever. Then I have an NSScrollView wrapping it (set up through the interface Builder).

Now the inner, custom, view must have a size larger than that which fits in the outer scroll view—for it to scroll. That much I realise. I have incidentally configured it so that the scroll view adjusts to the surrounding window’s size, but that shouldn’t matter.

I override my inner view’s -frame method to return a frame sized at least 1000×1000.

- (NSRect)frame {
    CGFloat w = 1000;
    CGFloat h = 1000;
    if (self.superview.bounds.size.width > w)
        w = self.superview.bounds.size.width;
    if (self.superview.bounds.size.height > h)
        h = self.superview.bounds.size.height;
    return NSMakeRect(0, 0, w, h);
}

Here’s the outcome, which I have trouble interpreting:

• I can scroll when the scroll view encloses an area smaller than 1000×1000

BUT

• The only area filled with colour (i.e. that my -drawRect: method has any effect on) is

  • as large as the scroll view’s bounds
  • located at (0,0. I use flipped, so that’s top left, and it ends up being outside the visible area after scrolling.
• The visible area that lies outside this irrelevant rectangle is not painted at all.

I don’t know anything beyond this point. It seems like the rect for drawing is clipped to the scroll view’s position in the window, and size, or something—but it does not take the scrolled “location” into account.

It should be noted that I don’t really expect anything else to happen. I feel I am missing a piece, but can’t find which. Sorry for the wall of text, but I can’t explain better right now. I hope it is easier to answer than it is to ask.

Regards and hope,

Not Rick Astley

Answer 1

It’s a very very very bad idea to overwrite -frame. There is so much that depends on the actual instance variable having a correct value. Instead try to set the frame to the one you want using setFrame:, that might fix all your problems if you’re lucky…