NSOutlineView setNeedsDisplayInRect calls fail

I have an NSOutlineView that uses a custom NSCell subclass to draw an NSProgressIndicator. Each NSCell has a refreshing property that is set by the NSOutlineView delegate willDisplayCell:forItem: method, like so:

- (void)outlineView:(NSOutlineView *)outlineView willDisplayCell:(id)cell forTableColumn:(NSTableColumn *)tableColumn item:(id)item
{
    cell.refreshing = item.refreshing;
}

Each item instance contains an NSProgressIndicator that is started and stopped dependent upon whether that particular item is refreshing.

- (NSProgressIndicator *)startProgressIndicator
{
    if(!self.progressIndicator)
    {
        self.progressIndicator = [[[NSProgressIndicator alloc] initWithFrame:NSMakeRect(0, 0, 16.0f, 16.0f)] autorelease];
        [self.progressIndicator setControlSize:NSSmallControlSize];
        [self.progressIndicator setStyle:NSProgressIndicatorSpinningStyle];
        [self.progressIndicator setDisplayedWhenStopped:YES];
        [self.progressIndicator setUsesThreadedAnimation:YES];
        [self.progressIndicator startAnimation:self];
    }

    return self.progressIndicator;
}
- (void)stopProgressIndicator
{
    if(self.progressIndicator != nil)
    {
        NSInteger row = [sourceList rowForItem:self];

        [self.progressIndicator setDisplayedWhenStopped:NO];
        [self.progressIndicator stopAnimation:self];
        [[self.progressIndicator superview] setNeedsDisplayInRect:[sourceList rectOfRow:row]];
        [self.progressIndicator removeFromSuperviewWithoutNeedingDisplay];

        self.progressIndicator = nil;
    }

    for(ProjectListItem *node in self.children)
    {
        [node stopProgressIndicator];
    }
}   

The items NSProgressIndicator instances are stopped and started within my NSCell's drawInteriorWithFrame:inView: class, like so:

- (void)drawInteriorWithFrame:(NSRect)cellFrame inView:(NSView *)controlView
{
    if(self.refreshing)
    {
        NSProgressIndicator *progressIndicator = [item progressIndicator];
        if (!progressIndicator)
        {
            progressIndicator = [item startProgressIndicator];
        }

        // Set the progress indicators frame here ...

        if ([progressIndi开发者_开发问答cator superview] != controlView)
            [controlView addSubview:progressIndicator];

        if (!NSEqualRects([progressIndicator frame], progressIndicatorFrame)) {
            [progressIndicator setFrame:progressIndicatorFrame];
        }
    }
    else
    {
        [item stopProgressIndicator];
    }

    [super drawInteriorWithFrame:cellFrame inView:controlView];
}

The issue I'm having is that although the NSProgressIndicators are correctly told to stop, the calls to stopProgressIndicator have no effect. Here's the code that fails to trigger the refresh of the NSOutlineView row in question. I've manually checked the NSRect returned by my call to rectOfRow and can confirm that the value is correct.

[self.progressIndicator setDisplayedWhenStopped:NO];
[self.progressIndicator stopAnimation:self];
[[self.progressIndicator superview] setNeedsDisplayInRect:[sourceList rectOfRow:row]];
[self.progressIndicator removeFromSuperviewWithoutNeedingDisplay];

self.progressIndicator = nil;

When the NSOutlineView finishes refreshing all of its items it triggers a reloadData: call. This is the only thing that seems to reliably update all of the cells in question, finally removing the NSProgressIndicators.

What am I doing wrong here?

It's bad practice to mess with view hierarchies while things are getting drawn. The best thing to do would be to use an NSCell version of NSProgressIndicator, but AppKit doesn't have such a thing. The solution described in Daniel Jalkut's answer to a similar question is probably the fastest path to what you want. Here's the basic idea:

Rather than use the refreshing variable to switch paths during drawing, observe your items' refreshing state. When it becomes true, add an NSProgressIndicator as a subview of your NSOutlineView at the item's position given frameOfCellAtColumn:row: (it can be convenient to set up a column for the progress indicators on the far right). When it becomes false, remove the corresponding progress indicator. You will also want to be sure to set the autosizing flags appropriately on these progress indicators so they move around as the outline view gets resized.