How to activate a custom screensaver preview in Cocoa/Obj-C?

I have created a fairly simple screensaver that runs on Mac OS 10.6.5 without issue.

The configuration screen has accumulated quite a few different options and I'm trying to implement my own preview on the configureSheet window so the user (just me, currently) can immediately see the effect of a change without having to OK and Test each change.

I've added an NSView to the configureSheet and set the custom class in Interface Builder to my ScreenSaverView subclass. I know that drawRect: is firing, because I can remove the condition for clearing the view to black, and my custom preview no longer appears with the black background. Here is that function (based on several fine tutorials on the Internet):

- (void)drawRect:(NSRect)rect
{
   if ( shouldDrawBackground ) 
   {
      [super drawRect:rect];
      shouldDrawBackground = NO;
   }
   if (pausing == NO)
      [spiroForm drawForm];
}

The spiroForm class simply draws itself into the ScreenSaverView frame using NSBezierPath and, as mentioned, is not problematical for the actual screensaver or the built-in System Preferences preview. The custom preview (configureView) frame is passed into the init method for, um, itself (since its custom class is my ScreenSaverView subclass.) The -initWithFrame method is called in configureSheet before returning the configureSheet object to the OS:

[configureView initWithFrame:[configureView bounds] isPreview:YES];

Maybe I don't have to do that? It was just something I tried to see if it was required for drawing.

I eventually added a delegate to the configureSheet to try triggering the startAnimation and stopAnimation functions of my preview via windowWillBeginSheet and windowW开发者_如何学JAVAillEndSheet notifications, but those don't appear to be getting called for some reason. The delegate is declared as NSObject <NSWindowDelegate> and I set the delegate in the configureSheet method before returning the configureSheet object.

I've been working on this for days, but haven't been able to find anything about how the OS manages the ScreenSaverView objects (which I think is what I'm trying to emulate by running my own copy.)

Does anybody have any suggestions on how to manage this or if Apple documents it somewhere that I haven't found? This isn't really required for the screensaver to work, I just think it would be fun (I also looked for a way to use the OS preview, but it's blocked while the configureSheet is activated.)

---

OK, there are a couple of 'duh' moments involved with the solution:

First of all, I was setting the delegate for the sheet notifications to the sheet itself. The window that the sheet belongs to gets the notifications.

Secondly, that very window that the sheet belongs to is owned by System Preferences, I don't see any way to set my delegate class as a delegate to that window, so the whole delegate thing doesn't appear to be a viable solution.

I ended up subclassing NSWindow for the configureSheet so that I could start and stop animation on my preview by over-riding the makeKeyWindow and close methods.

- (void) makeKeyWindow
{
   if (myPreview != nil)
      if ( ! [myPreview isAnimating])
      {
         [myPreview startAnimation];
      }
   [super makeKeyWindow];
}

I also had to add an IBOutlet for my preview object itself and connect it in Interface Builder.

Still working out a couple of issues, but now when I click on my screensaver Options button, my configureSheet drops down and displays its own preview while you set options. Sheesh. The hoops I jump through for these little niceties. Anyway, I like it. Onward and upward.